Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The construction and operating method of a new adiabatic calorimeter for measuring specific heats and… Selby, R. E. 1948

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1948_A7 S2 C6.pdf [ 6MB ]
Metadata
JSON: 831-1.0059098.json
JSON-LD: 831-1.0059098-ld.json
RDF/XML (Pretty): 831-1.0059098-rdf.xml
RDF/JSON: 831-1.0059098-rdf.json
Turtle: 831-1.0059098-turtle.txt
N-Triples: 831-1.0059098-rdf-ntriples.txt
Original Record: 831-1.0059098-source.json
Full Text
831-1.0059098-fulltext.txt
Citation
831-1.0059098.ris

Full Text

£/£<3 3 7 «5 2. <2 & THE CONSTRUCTION AND OPERATING- METHOD OP A NEW ADIABATIC CALORIMETER  FOR MEASURING SPECIFIC HEATS AND HEATS OF VAPORIZATION OF LIQUIDS. by R. E. SELBY, B.A.Sc. A Thesis submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of MASTER OF APPLIED SCIENCE o f CHEMICAL ENGINEERING. THE .UNIVERSITY OF BRITISH COLUMBIA September, 1948. THE CONSTRUCTION AND OPERATING METHOD OF A NEW ADIABATIC CALORIMETER FOR MEASURING SPECIFIC HEATS AND HEATS OF VAPORIZATION OF LIQUIDS. by R. E. Selby, B.A.So. „ ABSTRACT In the course of certain research work i t became necessary to measure the specific heat of li q u i d cis and trans decahydrate with great accuracy; The ordinary Williams and Da n i e l l e adiabatic calorimeter was found to be impractical* Several years ago a calorimeter for measuring the specific heat of l i q u i d hydrocarbons near room temperatures was developed at the IT. S, Bureau of Standards, A study of this instrument proved that i t would be the type desirable for the above measurement. Plans were obtained and altered to suit not only the measurements for cis and trans decalin but such hydrocarbons as are solid at room temperatures. During the past year such a calorimeter was constructed. It has also been so altered as to permit measurements of the latent heat of fusion to be made with 1 part in 1000* ACKNOWLEDGEMENTS I wish to acknowledge the co-operativeness of Dr. W. P. Seyer who d i r e c t e d t h i s work, and the a s s i s t a n c e g i v e n by Mr. E. Bart o n i n perf o r m i n g the necessary copper work. Table of Contents. I . I n t r o d u c t i o n . I I . R e s i s t a n c e Thermometers. (A) C o n s t r u c t i o n m a t e r i a l s and procedures used. (B) C a l i b r a t i o n of thermometers. (C) Data of C a l i b r a t i o n . (D) I n s t r u c t i o n s f o r s e r v i c i n g thermometers. I l l . Reference Block and Thermoelements. (A) C o n s t r u c t i o n of r e f e r e n c e b l o c k r i n g . (B) Thermometric and Thermoelement c o r r e l a t i o n . (C) Thermocouple groupings. (D) Thermocouple s t a n d a r d i z a t i o n . IV. C a l o r i m e t e r Cup. (A) C o n s t r u c t i o n of cup and s h i e l d . (B) Heating c o i l and l e a d s on cup. V. Envelopes and Envelope S h i e l d . (A) C o n s t r u c t i o n of system. VI. Vapour Tube Assembly. (A) C o n s t r u c t i o n and h e a t i n g c o i l s . (B) Cone j o i n t w i t h cup. V I I . Outer S h e l l . (A) C o n s t r u c t i o n . (B) Leads and vacuum p r o v i s i o n s . Table of Contents (Cont'd). V I I I . Bath and C i r c u l a t o r . IX. Switchboard Rheostats. (A) Arrangement. (B) P r e c a u t i o n s to be observed. X. Plunger S e a l . XI. Procedure f o r Taking Down the C a l o r i m e t e r . L i s t o f I l l u s t r a t i o n s . 1 C o n s t r u c t i o n and Assembly Drawing of the Instrument. 2 W i r i n g Diagram f o r the Instrument. 3 O r i g i n a l U.S. Bureau of Standards Design. 4 Photograph of P a r t i a l l y Assembled C a l o r i m e t e r . 5 Photograph of Thermometer Windings. 6 Photograph of Assembled C a l o r i m e t e r , Bath and Operating Panel Board. I . INTRODUCTION The U . S . Bureau of Standards has des igned and b u i l t a c a l o r i m e t e r f o r the measurement of heats of v a p o r i z a t i o n and heat c a p a c i t y of l i q u i d hydrocarbons . I t was r e q u i r e d here•>to adapt t h i s d e s i g n to our needs , ie.-» to i n c r e a s e the c a p a c i t y of the cup to about 450 c c . and to i n c r e a s e the dimensions of the equipment c o r r e s p o n d i n g l y . T h i s has been done and the new c a l o r i m e t e r has been l e f t i n an o p e r a t i v e c o n d i t i o n . F o r the purpose of ready r e f e r e n c e t o the o r i g i n a l d e s i g n j a copy of the o r i g i n a l paper and p r i n t has been i n c l u d e d as an appendix to t h i s p a p e r ; I I , RESISTANCE THERMOMETERS. (A) A r e s i s t a n c e thermometer c o n s i s t s of a l e n g t h of w i r e whose r e s i s t a n c e c h a r a c t e r i s t i c s versus temperature are known, wound on and supported by a frame w h i c h p e r m i t s a s m a l l r e l a -t i v e movement due to temperature expansion of the w i n d i n g upon i t . The w i n d i n g i s enc losed i n a s u i t a b l e hous ing and l e a d s from the w i n d i n g are brought through t h i s hous ing t o be connected, to a wheat stone b r i d g e . Thermometers commonly em-p l o y e d have a r e s i s t a n c e at the i c e p o i n t of r o u g h l y Zv$ ohms and consequent ly have a s m a l l i n c r e a s e of r e s i s t a n c e per degree r i s e of c o i l temperature (about ,01 ohm per degree c e n t i g r a d e ) , which n e c e s s i t a t e s accura te d e t e r m i n a t i o n s o f the c o i l r e s i s -tance t o determine i t s temperature ; T h i s c a l o r i m e t e r i s p r o -v i d e d w i t h two r e s i s t a n c e thermometers, one f o r cont inuous measurements and the second f o r a cheok on the f i r s t , each having an i c e p o i n t r e s i s t a n c e of about 40 ohms*. These c o i l s each have a r e s i s t a n c e increment of about .16 ohms p e r degree c e n t i g r a d e . The frames f o r these c o i l s were made from c l e a r mica s t r i p s •1." mm; t h i c k , out to s i z e , J"»9 mm. wide and 7.7 mm. l o n g , by c lamping a mica sheet between the faces of a d i e h e l d f i r m l y i n a v i s e , and c u t t i n g the exposed sheet away f rom the d i e w i t h a sharp r a z o r b l a d e . The d i e c o n s i s t s of two p i e c e s of l / 4 x i / 4 m i l d s t e e l bars N about 7 inches l o n g , w h i c h have been d r i l l e d f o r t h r e e #4 machine screws f o r a l i g n m e n t . When b o l t e d together these two b a r s were machined down so t h a t t h e i r common f a c e had a w i d t h o f 5>9 mm. The f a c e s i n contac t were t h e n ground t o smoothness w i t h f i n e carborundum p a s t e , a l l t r a c e s o f w h i c h were removed by w i p i n g the d i e w i t h e t h e r . The edges o f the mica s t r i p s made i n t h i s d i e were sharp and q u i t e f r e e f rom e x f o l i a t i o n . Each s t r i p was then n o t c h e d , f o r t y - f i v e notches b e i n g out i n a l e n g t h of 6 cm* on each edge; The d i e used f o r t h i s o p e r a t i o n was made i n the f o l l o w i n g manner. Two p i e c e s of 1/4 x 1/2 b r a s s 9 i n c h e s l o n g were s o l d e r e d toge ther on l / 2 i n c h f a c e s , U e i n g h e l d tinder p r e s s u r e i n a v i s e w h i l e the s o l d e r s e t . Three h o l e s were d r i l l e d , one near each e x t r e m i t y of the composite b a r and one t h r e e i n c h e s from one end', #4 screws were used t o b o l t the two h a l v e s toge ther to f u r t h e r r e s i s t the s p l i t t i n g tendency of l a t h e centers and to serve as a l ignment screws l a t e r . A s e c t i o n of the b a r n i n e cm. l o n g was machined down to 5»9 mm. d i a . F o r t y - f i v e i n d i v i d u a l grooves ;45 mm. wide were machined 1 .3 mnu between centers w i t h a square-nosed c u t - o f f t o o l to a groove depth of .95 mm. The two h a l v e s o f the composite bar were then sweated a p a r t , the s o l d e r removed and the common f a c e s smoothed to a c l o s e f i t ' . The mica s t r i p s prepared by the p r e v i o u s o p e r a t i o n were set up i n t h i s d i e so . t h a t the f i r s t groove appeared about .5 cm. f rom one end, the al ignment screws were t i g h t e n e d and the d i e was f i x e d f i r m l y i n a s m a l l v i s e . The mica exposed i n the b r a s s grooves was removed by f i l i n g i t away w i t h a l e n g t h of . 4 5 mm. d i a . p i a n o -w i r e h e l d t a u t i n a m e t a l bow. T h i s w i r e was roughened by r u b b i n g i t l a t e r a l l y w i t h a coarse carborundum s t o n e , and b e i n g of the same diameter as the w i d t h of the grooves i n the die*-i t cut sharp-edged notches w i t h rounded bottoms i n the mica s t r i p s . Fext ; , each s t r i p was s l o t t e d f o r a d i s t a n c e o f 4 cm. from one end . The d i e used f o r t h i s o p e r a t i o n was made from f o u r p i e c e s of 1/4 x l / 4 m i l d s t e e l seven i n c h e s l o n g . The f o u r p i e c e s were grouped i n p a i r s and a d e p r e s s i o n of . 15 mm. and about 6 cm. l o n g was f i l e d i n one face of one b a r o f each p a i r . The two bars o f each p a i r were then r i v e t e d t o g e t h e r w i t h three s t e e l r i v e t s , so t h a t the depress ions formed c o r r e s p o n d i n g s l o t s i n eaoh p a i r ; The two composite b a r s were a l i g n e d so t h a t the two s l o t s mated and were then d r i l l e d f o r a l i g n i n g screws; The mica s t r i p s were taken a f t e r the n o t c h i n g o p e r a t i o n and set up i n t h i s d i e so t h a t a f o u r cm, l e n g t h was exposed a t the s l o t on the c e n t e r - l i n e of the s t r i p ; The exposed, mica was cut out w i t h a narrow-edged r a z o r b l a d e to p r o v i d e a s h a r p l y - d e f i n e d s l o t ; A p a i r of mica s t r i p s were s l o t t e d from o p p o s i t e ends so t h a t when they were assembled i n t o a c r o s s i n the next oper -a t i o n the notches around the c i rcumference of the c r o s s would l i e on two separate hel loes/* each h e l i x h a v i n g a t r a v e l of 2 ; 6 mm; f o r each t u r n around the f rame; When each s t r i p was removed from t h i s d i e e i g h t h o l e s were d r i l l e d i n at a d i s t a n c e o f 1;5 mm. from the c e n t e r l i n e . One h o l e i s d r i l l e d on each s i d e of the c e n t e r l i n e h a l f way a l o n g the .j? cm. c l e a r space at the end and three e q u a l l y - s p a c e d h o l e s on e i t h e r s i d e of the c e n t e r l i n e a t the other end. These h o l e s were made w i t h a d r i l l made from a 1 and l / ,2 i n c h l e n g t h of .2.5 mm. d i a . s t a i n l e s s s t e e l w i r e ground to a f l a t c u t t i n g p o i n t and t u r n i n g at a p p r o x i m a t e l y 4000 r . p . m ; The mica s t r i p s were l a i d on a f l a t p i e c e of cork* then centered under the d r i l l and were f e d s h a r p l y i n t o the d r i l l ; T h i s procedure produced h o l e s w i t h adequate c l e a r a n c e f o r the ; 1 mm. p l a t i n u m l e a d s to be i n s e r t e d l a t e r , and w i t h a minimum of s p a l l i n g ; Each mica frame was assembled i n a j i g and h e l d ready t o be wound w i t h a p l a t i n u m r e s i s t a n c e c o l l . T h i s j i g was made from f o u r 1/4 x l/4 b r a s s b a r s about seven inches l o n g , s o l d e r e d together t o form a composite 1/2 x 1/2 i n c h b a r ; T h i s compo-s i t e b a r was set up i n a l a t h e by mounting one end i n a f o u r * jawed chuck and c e n t e r i n g the- o ther end, A s i x - i n c h l e n g t h of t h i s b a r was t u r n e d down i n t o a s h a f t t h r e e - e i g h t h s i n c h d i a . T h i s composite s h a f t was then mounted i n a t h r e e - j a w ohuok and t u r n e d down i n h a l f i n c h s e c t i o n s to a r o d 3»9 mm. i n d i a m e t e r . When the f o u r p a r t s of t h i s mandrel were sweated a p a r t and c l e a n e d , they formed the j i g f o r assembl ing t h e mica frames f o r when the f o u r quartern-round, p i e c e s were h e l d i n p o s i t i o n w i t h e l a s t i c bands , the o l e f t s between them*appeared as a c r o s s i n t o whioh the f i r s t mica s t r i p of a p a i r c o u l d be I n s e r t e d ( w i t h i t s s l o t towards the open end o f the c l e f t s ) and then the second s t r i p o f the p a i r c o u l d be t h r u s t t h i s one i n the j i g and s l i d i n t o the h e l i c a l a l ignment p r e v i o u s l y d e s o r i b e d ; The f o u r q u a r t e r * r o u n d ends were then,bound to ensure s t e a d i n e s s o f the mandrel i n the subsequent w i n d i n g o p e r a t i o n . The w i r e used f o r w i n d i n g the r e s i s t a n c e f i l a m e n t of the thermometers was 300 cm. o f .1 mm. nominal d i a . (39 B&S ga . ) i n each oase . I n o r d e r i n g ^ the s p e c i f i c a t i o n s f o r t h i s w i r e were t h a t i t should be hard-drawn p l a t i n u m .1 mm. d i a ; , : f r e e f rom s u r f a c e d e f e c t s and t h a t i t s r e s i s t a n c e at 100 degrees c e n t i -grade must have a r a t i o of not l e s s than 1.391 t o i t s r e s i s -tance at^O degrees c e n t i g r a d e . I n subsequent c a l i b r a t i o n s each f i l a m e n t of the thermometers employed i n the o a l o r i m e t e r 6,. were found to f i l l these r e q u i r e m e n t s . The procedure used i n making and assembl ing each f i l a m e n t was as f o l l o w s . The w i r e was l a i d out on a c l e a n s u r f a c e and h e l d under a l i g h t t e n s i o n f o r measuring o f f the r e q u i r e d l e n g t h by a t t a c h i n g a l i g h t copper w i r e t o one end of the p l a t i n u m w i r e and a n c h o r i n g t h i s copper w i r e , then unwinding the ' s p o o l so t h a t no t w i s t s were put : i n t o the p l a t i n u m . The w i r e was cut and a l e n g t h of l i g h t copper w i r e was a t t a c h e d at the new end; The e x t r a l e n g t h s of p l a t i n u m w i r e were used l a t e r f o r l e a d s ; A l a t h e was adapted f o r f o r m i n g the p l a t i n u m w i r e i n t o a h e l i x by removing the t a i l center and i n s e r t i n g i n t o the center tube a one- foot l e n g t h of tube capped a t one e n d ; T h i s cap was d r i l l e d w i t h a o n e - s i x t e e n t h i n c h diameter h o l e on c e n t e r . The i n s e r t e d tube had a s l i d i n g f i t i n t o the t a i l c e n t e r t u b e . A j i g f o r the l a t h e chuck was madle from a f o u r - i n c h l e n g t h of one i n c h b r a s s r o d , by d r i l l i n g a o n e - s i x t e e n t h i n c h h o l e l/2 i n c h deep on i t s a x i s . The mandrel on which the c o i l was wound was a t h r e e f o o t l e n g t h of .25 mm. d i a . s t a i n l e s s s t e e l p iano w i r e passed through the ho le i n the cap of the t a i l p i e c e tube and c l i p p e d i n t o the hole o f the chuck j i g . The f r e e end of the mandrel a t the cap was c l i p p e d through a s p h e r i c a l - s h a p e d s t e e l b u t t o n * o i l e d and f r e e to r o t a t e on the cap as a b e a r i n g . The l a t h e was set i n mot ion and the r o t a t i n g s t e e l w i r e mandrel was brought to the c o r r e c t w i n d i n g t e n s i o n b y l o a d i n g the t a i l p i e c e tube a x i a l l y w i t h weights hung over a p u l l e y i n a l ignment w i t h the mandre l i The l a t h e was stopped and the two foot copper l e a d on the p l a t i n u m w i r e was a t t a c h e d to the m a n d r e l ' a t the chuck j i g ; The p l a t i n u m w i r e was h e l d under a t e n s i o n of 10 gm. "by p a s s i n g the copper l e a d at the o ther end of the p l a t i n u m w i r e over a p u l l e y and a t t a c h i n g t h i s weight to i t ; The l a t h e was set i n mot ion at the speed of about 200 r ; p . m ; and kept t u r n i n g u n t i l the p l a t i n u m w i r e and a s h o r t l e n g t h of the end copper lead-were wound on the mandre l ; The t u r n s of p l a t i n u m w i r e on the mandrel were h e l d i n c l o s e contac t d u r i n g w i n d i n g . Whi le s t i l l on the m a n d r i l j the end copper l e a d was cut away from the p l a t i n u m c o i l . Then h o l d i n g the f r e e end of the p l a t -inum c o i l between the f i n g e r s , the l a t h e r e v e r s e d a t low speed f o r about 40 r e v o l u t i o n s . T h i s unwound the p l a t i n u m c o i l s u f -f i c i e n t l y to g i v e i t a f r e e s l i d i n g mot ion a l o n g the m a n d r e l , a l t h o u g h the adjacent t u r n s o f the c o i l s t i l l appeared t o , t h e eye t o be i n c o n t a c t . A f t e r t h i s , the oopper l e a d at t h e , j i g end of the mandrel was f r e e d from the p l a t i n u m c o i l . The w i r e mandrel i t s e l f was cut about t h r e e i n c h e s e i t h e r s i d e of the p l a t i n u m c o i l wound upon i t ( the p l a t i n u m c o i l a t t h i s stage was about 12 i n c h e s l o n g ) . One end of the s e c t i o n o f the man-d r e l thus removed was honed to smooth o f f sharp edges caused by n i p p i n g the w i r e ; The p l a t i n u m c o i l was s l i d o f f t h i s end of the mandrel onto a c l e a n s u r f a c e . A 1 cm. l e n g t h of w i r e was unwound at each end of the c o i l to r e c e i v e the p o t e n t i a l t e r m i n a l l eadsj two o f which are a t t a c h e d at each end of the c o i l ; A t t a c h i n g these l e a d s i s a s imple but somewhat d e l i c a t e o p e r a t i o n w h i c h c o n s i s t s of s i l v e r - s o l d e r i n g a 12 cm. l e n g t h of . 1 mm. d i a . . p l a t i n u m wfre r e f e r r e d t o p r e v i o u s l y , a t i t s m i d -p o i n t I n the form of a T across the 1 cm. s t r a i g h t n e d l e n g t h at . 8. each end of the platinum c o i l * The c o i l i s l a i d on a block about three inches thick with i t s end projecting a half inch over the edge of the block. The soldering flame was adjusted so that i t was about one eighth of an inch long, with a sugges-tion of a oxidizing cone immediately at the burner tip using a small acetylene torch. The end of the c o i l was moistened with a small amount of borax solution applied to i t with a brush < and dried.out with this flame a l i t t l e distance from i t . The point of the wire thus,prepared was again moistened and a very small sliver of high melting point silver-solder was l a i d upon the point where i t was held by the moist borax film. The center of the flame was brought to bear upon the silver-solder from: underneath and the sliver fused readily to form a spherical globule close to the end of the wire; The 12 cm. lead length was bent at i t s mid-point into a Y and the point of,this V was treated with borax in the manner described for the c o i l end. With one hand the point of the 7 was held in contact with the bead of silver-solder, and with the other the tip of the flame was held under the bead. Fusion at the bead was accomplished in about two seconds in each case, resulting in a substantial joint. This procedure was repeated for the other end of the c o i l . Next, the c o i l was stretched to a length of two feet between beads.: This resulted in a helix having turns of quite even,travel. The mid-point of the helix was then stretched slightly more open for about l/2 cm. length and the helix was doubled about this point. The mandrel w i t h the mica frame set up i n i t as p r e v i o u s l y d e s c r i b e d , was l a i d i n a h o r i z o n t a l p o s i t i o n and the m i d - p o i n t o f the doubled h e l i x was looped over and p r e s s e d i n t o the f i r s t p a i r o f notches on one l imb of the c r o s s . A 1 gm. weight i s suspended from the s o l d e r bead at each f r e e end of the c o i l to p r o v i d e w i n d i n g t e n s i o n . The c o i l was wound onto the mica frame by r o t a t i n g the mandrel s l o w l y by hand, making sure t h a t each t u r n o f the c o i l l a y w e l l i n t o the bottom o f i t s g r o o v e . On r e a c h i n g the ends o f the c o i l one l e a d branch from each j o i n t was threaded through the three h o l e s p r o v i d e d on i t s l i m b j thus a n c h o r i n g the ends of the c o i l to the frame• The b i n d i n g s around the f o u r q u a r t e r s o f the mandrel were cut away and the mandrel wi thdrawn, a p i e c e a t a time^ from under the c o i l . The o ther branch at each j u n c t i o n was then threaded through i t s a p p r o p r i a t e l i m b and the l e a d j o i n t s were drawn down t i g h t l y i n t o the f rame. I t was apparent at t h i s s tage t h a t . t h e looped end of the c o i l would r e t a i n i t s p o s i t i o n w i t h o u t b e i n g t i e d down w i t h a l o o p threaded through the f o u r h o l e s p r o v i d e d f o r t h a t purpose at i t s end of the frame, and so t h i s o p e r a t i o n was o m i t t e d . The c o i l s were ready f o r t h e i r h o u s i n g s . The o r i g i n a l c o n s t r u c t i o n of the thermometer housings c o n s i s t e d of 6.25 o . d . p l a t i n u m tube w i t h a r e e n t r a n t ; l e a d -w i r e cap welded i n t o i t , and when the thermometer w i n d i n g s had been i n s e r t e d and the l e a d - w i r e s drawn through h o l e s i n t h i s r e e n t r a n t capj the hous ing tube was spun down at the open end to r e c e i v e a g l a s s tube through which the thermometer was evacuated and b a c k - f i l l e d w i t h h e l i u m gas , whereupon the 10 * thermometer was sealed, by c l o s i n g the g l a s s t u b e ; T h i s s e r i e s of o p e r a t i o n s , p a r t i c u l a r l y the s p o t - w e l d i n g , c a l l e d f o r equipment which I s not a v a i l a b l e h e r e . F u r t h e r * on account o f the present excess ive c o s t o f p l a t i n u m , the use of a s u b s t i t u t e m a t e r i a l was thought a d v i s a b l e * There were a number of f a c t o r s t o be c o n s i d e r e d i n a r r i v i n g at an a l t e r n a t i v e d e s i g n f o r the thermometer h o u s i n g s . A p a r t from p r o v i d i n g mechanica l p r o t e c -t i o n f o r i t s w i n d i n g , each tube 3/s the h e a t - t r a n s m i t t i n g agent between the c a l o r i m e t e r body and t h i s w i n d i n g . Thus* p r o v i d i n g t h a t a p p r e c i a b l e heat g r a d i e n t s dp not e x i s t a long the h o u s i n g tube* the meta l employed i n i t s c o n s t r u c t i o n i s of l i t t l e moment * A f t e r a r e v i e w of the m a t e r i a l s commonly used f o r t h i s purpose* n i c k e l was d e c i d e d upon, and hard-drawn n i c k e l t u b i n g 6*25 mm. o*d* and ,15 mm. w a l l t h i c k n e s s was secured from the I n t e r n a t i o n a l N i c k e l Co . of America* I t must be remembered t h a t f i n a l l y the thermometers were mounted i n heavy copper t u b i n g , and i t w i l l be seen t h a t t h i s copper t u b i n g w h i c h has a v e r y h i g h heat d i f f u s i v i t y * w i l l ensure a minimum of heat g r a d i e n t s i n i t s enc losed n i c k e l t u b e , which has a c o m p a r a t i v e l y low heat d i f f u s i v i t y . Thus each w i n d i n g w i l l be surrounded by a hous ing at a - s u b s t a n t i a l l y u n i f o r m temperature , and w i l l be at an average temperature which w i l l g i v e a t r u t h f u l r e p r e -s e n t a t i o n of heat c o n d i t i o n s on the r e f e r e n c e b l o c k r i n g which supports copper tubes* A l s o , n i c k e l w i l l be q u i t e i n e r t under the c o n d i t i o n s i n which the c a l o r i m e t e r w i l l be operated* 11.. H i c k e l tubes were out to l e n g t h and cleaned;- A n i c k e l cap was prepared f o r each tube w i t h bare c l e a r a n c e ; Four h o l e s 1 .35 mm* d i a . were d r i l l e d on a 3 mnu c i r c l e i n -each c a p . Each cap was d r i v e n 2 mm. i n t o the end of a t u b e . A c i r c u l a r p l u g of t r a n s i t e , l / 4 i n c h l o n g , was pushed up the tube and h e l d i n p o s i t i o n under the n i c k e l p l a t e by means of a b r a s s r o d . U s i n g the n i c k e l cap as a t e m p l a t e , f o u r h o l e s were sunk i n t o the t r a n s i t e p l u g to a d e p t h of 1 mm. w i t h a l i 3 J ? mm; d r i l l . The b r a s s r o d c a r r y i n g the tube d e s c r i b e d was clamped v e r t i c a l l y i n a v i s e and the n i c k e l cap and the exposed p a r t of the n i c k e l tube i n s i d e were scoured w i t h s t e e l w o o l ; Four p l a t i n u m tubes , each 1 .33 o . d . , 1 mm. i i d ; , and 3 mm. l o n g * were set i n t o the f o u r h o l e s i n the n i c k e l cap and h e l d i n a v e r t i c a l p o s i t i o n by the r e c e p t a c l e s w h i c h ' h a d been d r i l l e d i n a l ignment i n ' t h e t r a n s i t e p l u g . A s m a l l q u a n t i t y of dry borax dust d i s t r i b u t e d over the cap between the tubes was used as a f l u x . A r i n g of s i l v e r s o l d e r w i r e was p l a c e d i n s i d e the open end of the tube around the p l a t i n u m tubes and s l i v e r s of s i l v e r s o l d e r were cut and wedged inbetween t h e p l a t i n u m t u b e s ; An a c e t y l e n e t o r c h was used to b r i n g the s o l d e r to the m e l t i n g p o i n t and the f o u r p l a t i n u m t u b e s , the n i c k e l e n d - p l a t e and the n i c k e l tube were s o l d e r e d t o g e t h e r i n one o p e r a t i o n . The p l a t i n u m tubes were bored i n t o round w i t h a 1 mnu d r i l l and p o l i s h e d * The hous ing tube-was then l i n e d w i t h a s t r i p of mica ;015 mm. t h i c k by f e e d i n g t h i s s t r i p i n t o the tube through a spade t o o l made f o r the purpose, 1 w h i c h p r o g r e s s i v e l y t u r n e d 12. the f l a t s t r i p i n t o a c i r c u l a r tube as i t was f o r c e d through the spade. -The frame and i t s w i n d i n g were mounted i n the hous ing tube by i n s e r t i n g a*#"0 B & S gauge copper w i r e through each o f the f o u r p l a t i n u m tubes and s o l d e r i n g each copper w i r e to i t s a p p r o p r i a t e p l a t i n u m l e a d . Then the f o u r copper w i r e s were drawn s i m u l t a n e o u s l y backward, drawing the p l a t i n u m l e a d s through the p l a t i n u m tubes and the frame i n t o the m i c a - l i n e d h o u s i n g , whereupon the f o u r copper wiires were cut away from the p l a t i n u m l e a d s . A tube o f Pb g l a s s *9 mm. o . d . and * I J " mm. i . d * was threaded a l o n g each l e a d w i r e i n t o and beyond-each p l a t i n u m tube f o r a d i s t a n c e of about 3mm» The h o u s i n g tube was then supported v e r t i c a l l y and these f o u r l e a d g l a s s tubes were sea led s i m u l t a n e o u s l y t o the p l a t i n u m w i r e s and tubes by f u s i n g them i n an oxy-ace ty lene f l a m e . A t h r e e - i n c h l e n g t h of copper t u b i n g t h r e e t h i r t y - s e c o n d s i n c h o . d . and o n e - s i x t e e n t h i n c h i * d . was f i t t e d w i t h a n i c k e l d i s c a t one end* The d i s c was s i l v e r - s o l d e r e d to the copper tube and the copper tube p r o j e c t i n g through the d i s c was f l a r e d over the d i s c w i t h a center -punch to prevent s e p a r a t i o n of the two i n the next s o l -d e r i n g o p e r a t i o n . The n i c k e l tube w i t h i t s w i n d i n g was sup-p o r t e d v e r t i c a l l y a g a i n w i t h the open end up and the copper tube c a r r y i n g the n i c k e l d i s c was clamped i n a l ignment w i t h the n i c k e l d i s c f o r c e d about 2 mm. i n t o the hous ing t u b e ; A r i n g of s i l v e r - s o l d e r was p l a c e d around the copper tube i n the r e c e p t a b l e thus formed* The s o l d e r was f u s e d , comple t ing the hous ing* 1 3 . The thermometers were now annealed f o r n i n e hours at a p p r o x i m a t e l y 475° c e n t i g r a d e ; To p r e c l u d e t h e p o s s i b i l i t y o f f a i l u r e o f the thermometers due to oracks d e v e l o p i n g l a t e r i n the g l a s s - t o - p l a t i n u m s e a l , the thermometers were c leaned o u t -s i d e and g i v e n s e v e r a l c o a t i n g s of c l e a r g l y p t a l l a c q u e r . The thermometers were baked f o r two hours at 1 1 0 ° o e n t i g r a d e a f t e r each a p p l i c a t i o n of l a c q u e r . Each thermometer was evacuated through i t s oopper tube and was found to h o l d a vacuum of one m i c r o n , as a t e s t of the h o u s i n g . L a t e r , the thermometers were connected by wax s e a l s a t the oopper tubes to another system, and were evacuated and f l u s h e d out w i t h oxygen gas s e v e r a l t i m e s , ^and f i n a l l y the tubes were f i l l e d w i t h oxygen a t o n e - t h i r d atmosphere.. The copper tubes were cr imped about 1 ; cm. from the e n d - p l a t e , cut o f f a t the c r i m p , and immediate ly s o l d e r e d . As an a l t e r n a t i v e t o h e l i u m whioh i s not r e a d i l y a v a i l a b l e h e r e , :oxygen was d e c i d e d upon a f t e r c o n s u l t i n g Webber, (who suggests t h a t an o x i d i z i n g atmosphere i s an advantage i n an r e s i s t a n c e thermometer.) (B) The thermometers were c a l i b r a t e d by d e t e r m i n i n g t h e i r r e s i s t a n c e s i n comparison w i t h a s tandard p l a t i n u m r e s i s t a n c e thermometer at ( l ) the i c e p o i n t and (2) b o i l i n g p o i n t of water and (3) a t room temperature . I n t h i s p r o c e d u r e ; temporary #30 B&S g a . copper l e a d s were " so ldered to the p l a t i n u m l e a d s o f each thermometer and the thermometers were lowered by • means of these l e a d s i n t o f i f t e s n - i n c h p y r e x t e s t - t u b e s whioh were clamped v e r t i c a l l y a t a t e n i n c h immersion i n a f o u r - l i t r e pyrex beaker w h i c h had been lagged w i t h asbestos sheet . T h i s 14 . bath, was ag i ta ted , f o r a l l measurements at a l l temperatures except those at the i c e p o i n t * The two thermometers employed, i n the c a l o r i m e t e r were g r a t i f y i n g l y c o n s i s t e n t * The thermo-meters d i s p l a y e d , a somewhat g r e a t e r l a g than the s tandard r e s i s t a n c e thermometer which i s the b l a d e immersion t y p e , v e r y r e s p o n s i v e t o temperature changes* However, t h i s e f f e c t i s of no consequence s i n c e the r a t e of h e a t i n g i n the c a l o r i m e t e r i s q u i t e slow* F i n a l l y , the copper tubes of the r e f e r e n c e b l o c k r i n g were reamed out to a snug f i t f o r the thermometers and the p o t e n t i a l t e r m i n a l l e a d s of each thermometer were connected to #30 g a . > double cotton-wound l a c q u e r e d copper e x t e n s i o n l e a d s w i t h s o f t s o l d e r . To f o r s t a l l a c c i d e n t a l s h o r t i n g between these j o i n t s a l l the connect ions were g i v e n t h r e e coats o f g l y t o l l a c q u e r * (S) The method by which the r e s i s t a n c e thermometers were c a l i b r a t e d has been d e s c r i b e d . The d e t a i l e d r e a d i n g s are i n the l a b . n o t e - b o o k . Here are the da ta from w h i c h the O a l l e n d a r constant f o r each thermometer and a r e a d y - r e f e r e n c e t a b l e f o r r e a d i n g the temperature on the I n t e r n a t i o n a l S c a l e can be prepared* The thermometer used as a s tandard was the Leeds and K o r t h r u p #679368, F i l i n g Uhumber 1 1 1 - 1 , 111247, NBS 921 (June 6 , 1947) HFS, AM* R 0 2 5 . 5 4 6 i n t e r n a t i o n a l ohms, R - n n - Rn = C = . 0 0 3 9 2 3 4 o f O a l l e n d a r e q u a t i o n lOORo •= 1 . 4 8 * T h i s da ta was determined w i t h a 2 m i l l i a m p * c u r r e n t and an immersion of 22 cm. by L & N* 1 5 i , Standard C a l o r i m e t e r C a l o r i m e t e r (Not i n C a l -Thermometer T h e r m a l , - Therm. #2 o r imeter ) J u l y 17 0°C 25.54b" 4 4 . 3 4 4 45 .141 3 2 . 8 4 7 18 Room Temp. 2 7 . 5 9 0 4 7 . 8 7 3 4 8 . 7 3 3 3 5 . 4 5 5 20 rt 27 .724 4 8 . 1 0 5 4 8 . 9 7 1 3 5 . 6 1 7 1? B o i l i n g 3 5 . 5 4 5 6 1 . 6 4 2 6 2 . 7 8 5 4 5 . 5 5 7 The t a b l e i s to be read across w i t h the i n t e r p r e t a t i o n t h a t when the s tandard r e a d 2 5 . 5 4 6 ohmsi then #1 a t the same tempera-t u r e read 44.344 ohms, #2 ~ 45;141 ohms, and #3 •** 32 .847 ohms. Read each l i n e w i t h the same i n t e r p r e t a t i o n . I t w i l l be seen t h a t by u s i n g the r e a d i n g s i n the f i r s t l i n e ; the l a s t l i n e , and i n e i t h e r of the middle two l i n e s * ( e . g . J u l y 1 7 , 2 0 , 1 9 ) , the r e s i s t a n c e s of each thermometer are g i v e n at t h r e e p o i n t s i n the a n t i c i p a t e d range of the c a l o r i m e t e r . C a l c u l a t e the t r u e temperatures f o r these three p o i n t s from the r e a d i n g s on the s t a n d a r d . S ince the equat ion from w h i c h the C a l l e n d a r con-s t a n t i s d e r i v e d i s of the form a x 2 + bx + e, the cons tants i n t h i s equat ion can be determined from the three p o i n t s p r e v i o u s l y determined which must l i e on the curve f o r the e q u a t i o n . The r e f e r e n c e s f o r t h i s c a l c u l a t i o n are (1) B u l l e t i n of the I T . S . Bureau of S tandards , V o l . 1 3 , 1916, P 547 - E . F*. M u e l l e r . (2) Temperature Measurement and C o n t r o l , Weber, B l a k i s t o n P r e s s , 1941, Chap. V I I , p . 144. 16. (D) I f i t should ever be necessary to remove the w i n d i n g from a r e s i s t a n c e thermometer hous ing to s e r v i c e i t , t h i s procedure should be adopted . R e l i e v e the p a r t i a l vacuum i n the thermo-meter by d r i l l i n g a s m a l l h o l e not more t h a n 2 mm. from the end of the thermometer through w h i c h i t was evacuated or as an a l t e r - •• n a t i v e , out o f f the s o l d e r e d p o r t i o n of the copper e v a c u a t i o n tube and open t h i s tube w i t h a prober b e i n g c a r e f u l not t o t h r u s t the probe beyond the p o i n t where the tube i s s i l v e r -s o l d e r e d t o the h o u s i n g . :Clamp the thermometer v e r t i c a l l y on a r i n g s tand and r a i s e a beaker o f about 2N H C l under the t h e r -mometer u n t i l the housing tube i s immersed about one mm. i n the a c i d at the end where the l e a d s come out* The m e t a l up to t h i s p o i n t must have been scraped f r e e of l a c q u e r ; Then pass a c u r r e n t from a two v o l t b a t t e r y from the thermometer hous ing i n t o the s o l u t i o n and by t h i s means corrode away the immersed p o r t i o n of the n i c k e l h o u s i n g . Remove the thermometer and d r y i t t h o r o u g h l y i n an oven and r e v e r s e the c o r r o d i n g procedure f o r the other end. I t should now be p o s s i b l e to ease out the frame w i t h a r o d s l i g h t l y s m a l l e r than the t u b e . T h i s method of removal r u i n s the hous ing but i s g e n t l e on the w i n d i n g and frame, which are the most v a l u a b l e p a r t s of the thermometer* 17. I I I . REFERENCE BLOCK (A) C e n t r a l l y l o c a t e d i n the c a l o r i m e t e r body i s the r e f e r e n c e b l o c k which i s a heavy r i n g h e l d i n p o s i t i o n by e i g h t s t a i n l e s s s t e e l s t r a p supports , each screwed down i n d i v i d u a l l y to the f l a t s u r f a c e s of the r i n g w i t h a #4 machine screw. Four sup-p o r t s are anchored above the r i n g t o the upper envelope cap and f o u r are anchored below to the envelope s h i e l d cap r i n g . F o r ease i n m a c h i n i n g , t h i s r i n g was made of b r a s s . The two copper tubes which c a r r y the r e s i s t a n c e thermometers were mounted on the r i n g by f i l i n g deep grooves i n the l o w e r f a c e of the r i n g and making a s o l i d j o i n t between tubes and r i n g w i t h s o f t s o l d e r ; S ince the s o l d e r f u l l y surrounds the t u b e s , they are t h e r m a l l y i n t e g r a l w i t h the r i n g at the p o i n t s where they pass through the r i n g . The r i n g c a r r i e s 72 screws on i t s p e r i p h e r y , 36 on e i t h e r s ide of the squared groove machined around the p e r i p h e r y mid-way between the f l a t s u r f a c e s . T h i s r i n g serves as the thermal connec t ion between the r e s i s t a n c e thermometers and a l l the thermoelements i n the ins trument except #15; The manner i n w h i c h the thermal c o n n e c t i o n between thermoelements and the r e s i s t a n c e thermometers i s e s t a b l i s h e d i s as f o l l o w s . C o n s i d e r the r e p r e s e n t a t i v e element number 1 which i s a t t a c h e d to the bottom of the cup; The thermocouple i s formed from Leeds and Northrop double-pyrexed-wsapped duplex N o . 30 B & S g a . copper v s . copper -constantan w i r e s ; The end of the thermo-couple on the cup has been c l e a r e d o f i n s u l a t i o n and enamel 1 8 . f o r about one cent imetre from the end and. the two w i r e s have been t w i s t e d and s o f t - s o l d e r e d to a copper tab w h i c h was then trimmed to approx imate ly o n e - e i g h t h by t h r e e - s i x t e e n t h of an i n c h , and g i v e n two coats o f c l e a r g l y p t a l l a c q u e r over the tab and f o r a shor t d i s t a n c e up the g l a s s i n s u l a t i o n . A copper c l i p had been s o l d e r e d to the cup to r e c e i v e t h i s thermocouple t a b , w h i c h i s t h r u s t under the c l i p between two s m a l l s t r i p s o f mica ;05 mm. t h i c k , the c l i p b e i n g p r e s s e d down t i g h t l y over the tab a f t e r i t s i n s e r t i o n . A s m a l l q u a n t i t y o f l a c q u e r was a p p l i e d t o the mica l a t e r to ensure thermal contac t of the thermocouple w i t h the metal of the cup . The other end of the thermocouple w i r e s t e r m i n a t e a t the r e f e r e n c e b l o c k where the two w i r e s were separated and c leaned f o r a d i s t a n c e of about two c e n t i m e t e r s ; A n o . 30 g a . double-wrapped c o t t o n copper l e a d i s s o l d e r e d to each thermocouple w i r e ; These two j o i n t s are h e l d i n t o thermal contact w i t h the b r a s s r i n g between corresponding p a i r s of screws on the upper and lower l i n e s o f screws by b a c k i n g each screw out a l i t t l e f rom the r i n g and l a y i n g down a s t r i p of mica .05 mm. t h i c k between the two p a i r s of screws,and h o l d i n g the two j o i n t s t o t h i s mica s u r f a c e w i t h a t h i c k mioawjdge, whioh i s f o r c e d under the heads of the screws but over the two j o i n t s , and then t i g h t e n i n g down the f o u r screws to c l e n c h the wedge and the j o i n t s to the mica s t r i p below* T h i s j u n c t i o n was t r e a t e d w i t h l a c q u e r as was the j u n c t i o n at the c l i p . A l l the thermocouple j u n c t i o n s at the r i n g were anchored to the r i n g i n the same manner, p a r t i c u -l a r care b e i n g taken t o have the same t h i c k n e s s o f mica between 19; each thermocouple and the r e f e r e n c e b l o c k , and between each tab and i t s thermal contact w i t h the i n s t r u m e n t . T h i s assures t h a t any temperature l a g s t h a t do develop i n o p e r a t i o n w i l l be c o n s i s t e n t throughout the ins trument and thus make f o r s teady o p e r a t i o n . (B) I t w i l l be seen t h a t the temperature a t any p a r t of the ins t rument w i l l be t h a t i n d i c a t e d by a r e s i s t a n c e thermometer w i t h the a d d i t i o n a l g e b r a i c a l l y of the temperature d i f f e r e n c e between the r e f e r e n c e b l o c k and t h a t p a r t * which w i l l be g i v e n by a thermocouple . I n the case of o p e r a t i o n where the . c a l o r -i m e t e r i s b e i n g heated at a s teady r a t e , the e f f e c t s of thermo-couple l a g on the a c t u a l temperature w i l l be n i l s i n c e each j u n c t i o n of each thermocouple i s p r o t e c t e d w i t h a s i m i l a r t h i c k n e s s of mica f rom the s u r f a c e to w h i c h i t i s h e l d . The temperature of the r e f e r e n c e b l o c k i s h e l d c l o s e I n step w i t h the temperature of the sample by a h e a t e r wound i n t h e square groove r e f e r r e d to p r e v i o u s l y . R a d i a t i o n from the heated upper envelope s e c t i o n p a r t l y accounts f o r the h e a t i n g of t h i s b l o c k ; S u c c e s s f u l o p e r a t i o n of the r e f e r e n c e b l o c k r e q u i r e s s m a l l heat g r a d i e n t s around the r i n g and a l o n g the thermometer t u b e s ; which can be ach ieved by h a v i n g slow h e a t i n g of the c a l o r i m e t e r as a w h o l e . (C) Thermoelements #1, 2, 2, and 4 are l o c a t e d on the bottom and s i d e of the sample c u p . Thermoelement F o . J? i s l o c a t e d a t the base of the cup stem; The maximum a l l o w a b l e r a t e f o r h e a t i n g a sample w i l l be determined by o b s e r v a t i o n of the 20 i temperature d i s t r i b u t i o n around the oup at a number of h e a t i n g r a t e s f o r eaoh new type of sample h a n d l e d ; s i n c e each type o f l i q u i d w i l l have a d i f f e r e n t thermal d i f u s s i v i t y . The maximum a l l o w a b l e r a t e w i l l be t h a t which r e s u l t s i n no s i g n i f i c a n t d i f f e r e n c e s between any of these thermocouple temperatures . I n o p e r a t i o n , t o prevent heat l o s s f rom or unmeasured heat g a i n t o the cup and c o n t e n t s , thermocouple #6, l o c a t e d at t h e upper end of the oup stem, i s p a i r e d w i t h #5; The l e a d w i r e s from these two thermocouples are w i r e d on the ins trument p a n e l so t h a t the v o l t a g e s generated by the two thermocouples are i n o p p o s i t i o n a c r o s s a b a l l i s t i c galvanometer ; Any d e f l e c t i o n i n the galvanometer consequent ly i n d i c a t e s w h i c h of the thermo-couples i s at a l o w e r temperature , and an a u x i l i a r y s c a l e can be made f o r the galvanometer to read heat leakage a long the stem i n wat ts and an a p p r o p r i a t e c o r r e o t i o n can be r e a d i l y made t o the s imultaneous r e a d i n g s of the wattage i n p u t to the cup h e a t e r ; As soon a s - a d e f l e c t i o n i s n o t i c e d r e g a r d l e s s o f i t s d i r e c t i o n , the c u r r e n t through the oup stem guard heater wound at the end of the vapor tube must be a d j u s t e d a c c o r d i n g l y and the galvanometer brought t o b a l a n c e . I . E . , i f #6 i s too c o l d , boost t h i s c u r r e n t , i f #6 i s too h o t , cut the c u r r e n t down or o f f c o m p l e t e l y . Thermocouples 7 and 8 are l o c a t e d 180 degrees apar t on the c a l o r i m e t e r s h i e l d ; Thermocouples 10 and 11 are l o c a t e d 180 degrees apar t on the l o w e r envelope s h i e l d ; The l e a d s from these f o u r thermocouples are w i r e d on the ins t rument p a n e l so t h a t 7 and 8 are i n s e r i e s and 10 and 11 are i n s e r i e s . 21. The combined v o l t a g e s of each p a i r are put In o p p o s i t i o n across a second b a l l i s t i c galvanometer. This team operates i n a manner e x a c t l y analogous to the stem team, w i t h a d e f l e c t i o n i n d i c a t i n g a temperature d i f f e r e n c e between the c a l o r i m e t e r s h i e l d and the lower envelope s h i e l d and i n which d i r e c t i o n t h i s temperature d i f f e r e n c e l i e s . C o r r e c t i o n i n t h i s case i s achieved by a d j u s t i n g the c u r r e n t s p a s s i n g through both the upper envelope c o i l and the lower envelope c o i l i f these two c o i l s are not being run i n s e r i e s . As i n the case of the stem galvanometer, an a u x i l i a r y s c a l e can be p r o v i d e d f o r the r a d i a -t i o n l o s s or g a i n d i r e c t l y i n watts. Thermocouples 12 and 13 are l o c a t e d on the lower and upper envelope s e c t i o n s consecu-t i v e l y and are used to e s t a b l i s h the proper c u r r e n t s through the c o i l s on these envelopes to balance a g i v e n r a t e of h e a t i n g at the cup. Thermocouple No. 14 i s l o c a t e d on the tempering r i n g (1) to govern the c u r r e n t through the h e a t i n g c o i l on t h i s r i n g which boosts the temperature of the tempering r i n g and the upper envelope cap to that of the upper envelope s e c t i o n and (2) , to e s t a b l i s h the temperature of the s p l i t j u n c t i o n of #15. Thermocouple No. 15, whose w i r i n g i s the e x c e p t i o n r e f e r r e d to p r e v i o u s l y , has i t s connected j u n c t i o n on the j a c k e t tempering r i n g but i t s r e f e r e n c e j u n c t i o n i s h e l d to the tempering r i n g about one cm. away from thermocouple No. 14 w i t h the r e s u l t t h a t No. 15 g i v e s a d i r e c t measurement of the temperature d i f f e r e n c e between the outer copper e n c l o s u r e , which i s necess-a r i l y at the b a t h temperature, and No. 14 which i s taken as the 22. temperature o f the assembly I n s i d e . I t i s by means of No. 15 that the h e a t i n g c u r r e n t i n the b a t h i s r e g u l a t e d s i n c e the galvanometer across which #15 i s d i r e c t l y connected i n d i c a t e s the l a g i n bat h temperature. Thermocouple 9 i s used t o complete the survey i n conjunc-. t i o n w i t h 10 and 11 of the temperature g r a d i e n t s on the lower envelope s h i e l d , by ob s e r v i n g each i n d i v i d u a l l y with the student potentiometer. Thermocouple 16 i s not d i r e c t l y connected w i t h the opera-t i o n o f the c a l o r i m e t e r at a l l . I t s i n t e r n a l j u n c t i o n i s h e l d to the r e f e r e n c e b l o c k and the thermocouple wire i s brought d i r e c t l y from t h i s j u n c t i o n out of the instrument. I t s e x t e r n a l j u n c t i o n can be immersed i n an ice-and-water bath and i t can be wired to a r e l a y system to guard a g a i n s t o v e r h e a t i n g the whole c a l o r i m e t e r . (D) In order to wire the thermocouples c o r r e c t l y on the switch-board, e i t h e r i n s e r i e s or i n o p p o s i t i o n , i t was necessary to determine the p o l a r i t y of each thermocouple i n d i v i d u a l l y . T h i s was done f o r #1 to 14 i n c l u s i v e by t u r n i n g on the r e f e r e n c e r i n g heater f o r 30 seconds at 0.1 amp. without any other heat-i n g i n the instrument, and o b s e r v i n g the d e f l e c t i o n caused i n a galvanometer d i r e c t - c o n n e c t e d across each thermocouple i n t u r n . The leads of some thermocouples were then r e v e r s e d to have the galvanometer d e f l e c t i o n i n the same d i r e c t i o n f o r a l l thermo-couples. Thermocouple #15 was checked by s w i t c h i n g on the tempering r i n g h e a t e r f o r a sh o r t p e r i o d and, by a d j u s t i n g i t s 23. l e a d s , "brought to d e f l e c t the same as the o t h e r s . #16 needs no such c a l i b r a t i o n . Since thermocouple #13 has developed a short to the outer s h e l l , i t i s necessary to connect the upper and lower envelope heaters i n s e r i e s on the switchboard, and c o n t r o l t h e i r o p e r a t i o n by thermocouple #12. Since thermocouple #11 ap p a r e n t l y has a p a r t i a l s h o r t between i t s two copper l e a d connections at the r e f e r e n c e r i n g j u n c t i o n , i t i s necessary to use the temporary s h i e l d r a d i a t i o n c o n t r o l w i r i n g shown on the w i r i n g diagram. Both of these c o r r e c t i o n s are q u i t e adequate f o r o p e r a t i o n . IV. CALORIMETER CUP (A) The cup has a c a p a c i t y o f about 450 c c . but should not be f i l l e d w i t h more than about 350 c c . of l i q u i d . The bottom and si d e w a l l s of the cup are spun from a s o l i d sheet of 16 i n . ga. copper. The vanes which form a c e l l u l a r system i n s i d e the cup are so spaced that no p a r t i c l e o f l i q u i d i s more than 2.5 mm. d i s t a n t from e i t h e r a vane, the o u t s i d e s h e l l , or the c e n t r a l tube which supports the vanes. A l l i n s i d e s u r f a c e s o f the cup are t i n n e d w i t h 50-50 s o l d e r and t h i s f a c t should be borne i n mind i n c o n s i d e r i n g what samples are to be operated i n t h i s cup. (For any c o r r o s i v e l i q u i d another cup must be made of, say, s t a i n l e s s s t e e l throughout w i t h parent-metal welding. The h e a t i n g c o i l f o r such a cup would have to be wound a l l the way 24. up the s i d e s of the cup i n order to overcome the comparatively low t h e r m a l - d i f f u s i v i t y of .this m a t e r i a l , and would have to he pressed i n t o contact w i t h the s t e e l s h e l l w i t h a s k i n of annealed copper which would then he g o l d - p l a t e d . ) The c e n t r a l tube supp o r t i n g the vanes i s ^  i n . i . d . 20 ga. copper. I n order to f a c i l i t a t e ready removal of a sample i n the cup, grooves are cut i n t o the lower end of t h i s tube which r e s t s on the cup bottom and the lower edge of each vane i s coped to p r o v i d e an open w e l l about s i x t e e n t h o f an i n c h deep at the entrances of the centre tube. T h i s w i l l a l l o w a l o n g tube to be i n s e r t e d to the bottom of the cup when the plunger tube and diaphragm have been removed and the sample w i l l be removed through t h i s tube by s u c t i o n e x t e r n a l l y a p p l i e d . I f i t i s necessary to p r e s e r v e the sample i n t o t o , the diaphragm and plunger w i l l not be r e -moved but the plunger w i l l be s l i g h t l y withdrawn from the cup , stem and the sample w i l l be d r i v e n out by v a p o r i z i n g i t by means of the cup heater and w i l l be c o l l e c t e d by condensing i t s vapor i n a c o l d t r a p connected to the instrument through the vapor l i n e . I f i t should be necessary to apply a vacuum i n order to enable t h i s d i s t i l l a t i o n of a sample which would otherwise be decomposed, a vacuum pump w i l l be connected t o the side o f the c o l d t r a p removed from the Instrument. The vanes are made from 28 ga. copper. The cap.of the cup i s spun from 16 ga. copper to the same r a d i u s as the bottom. The stem i s made from -J- i n . i . d . 3/8 i n . o.d. s t a i n l e s s s t e e l , 18 N i . - 8 Cr., which was chosen f o r i t s low t h e r m a l - d i f f u s i v i t y . The stem i s h a r d - s o l d e r e d i n t o the cap and the i n s i d e of the 25. cap was t i n n e d b e f o r e t h i s assembly was s o l d e r e d i n t o the cup assembly as d e s c r i b e d . The outer r i m of the cap was spun down ^ i n . to a l l o w f o r a s t r o n g j o i n t w i t h the body. The upper end of the stem was ground to a sharp edge t o a c t as a seat f o r the plunger vapor s e a l d i s k . Now the cone vapor s e a l w i t h i t s a l i g n i n g thread was h a r d - s o l d e r e d to the stem and the i n s i d e of the cup was r i n s e d to remove any t r a c e s o f s o l d e r i n g f l u x . Small copper c l i p s were s o l d e r e d to the s h e l l a t . t h e p o s i t i o n s i n d i c a t e d on drawing No. f o r Nos. 1-5 and a s i m i l a r c l i p at the base of the cone vapor s e a l on the stem f o r No. 6. At t h i s stage the cup was g o l d - p l a t e d and brought to a f i n i s h l o c a l l y termed a " s c r a t c h p o l i s h " . IB) A one-hundred-ohm c o i l i s wound around the body to serve as the cup h e a t e r . To prevent s h o r t s d e v e l o p i n g between c o i l and cup t h i n s t r i p s of mica were cemented to the body wi t h g l y p t o l l a c q u e r and allowed to s e t , the c o i l was doubled on i t s e l f f o r no n - i n d u c t i v e n e s s , and wound over t h i s mica sheet. The j o i n t s between the c o i l and i t s No. 30 ga. copper leads were wound w i t h s i l k and l a c q u e r e d and the two l e a d s were housed i n a s i n g l e p i e c e of macaroni tube i n s o l a t i o n . To prevent damage to the c o i l by the compression sheath a padding of g l a s s wool was l a i d upon the c o i l and h e l d t i g h t w i t h mica s t r i p s and the sheath was compressed to t h i s wadding with two s t a i n l e s s s t e e l bands at the edges of the sheath. The bands were t i g h t e n e d u n t i l the sheath was i n con t a c t w i t h the s h e l l , by means of b r a s s machine screws through the lugs at the s p l i t 26. i n each s t e e l hand. The c o i l l e a d s pass out from the sheath through a small tunnel at the s p l i t i n the upper hand. The lea d s from the c o i l and the thermocouples Nos. 1, 2 and 3 pass up through h o l e s d r i l l e d i n the re c u r v e d r i m o f the c a l o r i m e t e r s h i e l d cap which i s p r e s s e d down over the top of the cup. About \ i n c h b e f o r e the heate r l e a d s r e a c h the stem a dummy l e a d i s s p l i c e d to each o f the l e a d s , g i v i n g f o u r l e a d s from the cup c o i l i n a l l , whose use i s e x p l a i n e d elsewhere. The lower c a l o r i m e t e r s h i e l d i s now attac h e d to the s h i e l d cap wi t h i t s bayonet j o i n t and the thermocouples No. 4, 7 and 8 are i n s e r t e d i n t h e i r c l i p s and t h e i r wires brought upwards on the ou t s i d e of the c a l o r i m e t e r s h i e l d cap. The f o u r leads from the cup c o i l serve the purpose some-what analogous to the f o u r p o t e n t i a l t e r m i h a l leads o f the r e s i s t a n c e thermometers, that i s , they enable the r e s i s t a n c e of that p a r t of the c i r c u i t which s u p p l i e s heat to the cup and contents to be determined at any temperature apart from the extraneous r e s i s t a n c e s from the j u n c t i o n s o f the dummy leads to the measuring Instruments on the panel board. T h i s i s done by measuring the i n d i v i d u a l r e s i s t a n c e s o f the f o u r l e a d s between the panel board and j u n c t i o n s , and of the h e a t i n g element between j u n c t i o n s , at a s e r i e s of temperatures to gi v e a c o r r e c t i o n t a b l e f o r the v a r i a b l e r e s i s t a n c e of the c u r r e n t -c a r r y i n g l e a d s . Switches on the instrument pa n e l are p r o v i d e d to f a c i l i t a t e these r e a d i n g s . 27. V . ENVELOPES AND ENVELOPE SHIELD (A) The upper and lower envelope system completely houses i n the r e f e r e n c e h l o c k , cup and lower envelope s h i e l d . T h i s envelope system, to which the r e f e r e n c e b l o c k i s a t t a c h e d by the e i g h t s t a i n l e s s s t e e l s t r a p s d e s c r i b e d elsewhere, i s supported by f o u r f i b e r s t r a p s between the tempering r i n g a t t a c h e d to the upper envelope cap and the j a c k e t tempering r i n g which i s s o l d e r e d to the outer s h e l l . These f o u r s t r a p s serve to a l i g n the envelope system c e n t r a l l y with the c a l o r i -meter cup and the outer s h e l l . The only c o n n e c t i o n between the envelope system and the cup i s the unavoidable one due to hea t e r and thermocouple l e a d s t r a v e l i n g from the cup stem to the r e f e r e n c e b l o c k r i n g . . 28. VI. VAPOUR TUBE ASSEMBLY (A) The vapour tube i s ^  i.d. five-eights o.d. stainless steel 18 Ni. 8 Cr.. It is aligned centrally with the outer shell by means of a brass flange soldered just below the vapour branch-line, and by a brass ring soldered around the tube just at the opening of the copper casing tube. The open end of the vapour tube carried the brass diaphragm receptacle. There are four heating coils wound on this vapour tube. One serves as the stem guard heater and three serve as heaters to prevent vapour condensation and runback during experiments on heat of vaporization. The leads for these latter three heaters are brought out through the lead duct but as yet are not connected to the instrument panel since i t w i l l be some time before they w i l l be used. It is not possible at this* time to suggest a maximum current for these vapour heaters. This is because the center and upper vapour heaters operate In a vacuum and are wound upon a stainless steel tube, both facts which result in the slow removal of heat from these coils, and they would easily burn out. The current passing through them when they are hooked up i n series should be regulated so that the thermocouple referred to i n the section on the Plunger Tube w i l l register a temperature a few degrees above thermocouples Nos. 4, 5 and 6. The leads for the center and upper vapour heaters are brought downwards past the brass aligning ring and then up through the lead duct. 29. (B) The vapour l i n e h a l f of the cone j o i n t was prepared i n the f o l l o w i n g manner. The vapour tube was b u i l t up at the end w i t h s t a i n l e s s s t e e l welding r o d . T h i s b u i l t - u p p o r t i o n was machined smooth i n the l a t h e . Next, the i n s i d e t h r e a d was cut w i t h a n i n e - s i x t e e n t h s i n c h tap while the tube was s t i l l mounted i n the l a t h e chuck, u s i n g the t a i l - c e n t e r of the l a t h e to a l i g n the tap to cut the t h r e a d true w i t h the tube. The i n s i d e cone was then cut at the base of the threads. T h i s s e r i e s of o p e r a t i o n s r e s u l t e d i n proper a l i g n -ment between the tube, thread and cone s e a t . The t h r e a d on the stem h a l f of the cone j o i n t was cut to a smooth f i t w i t h the i n s i d e thread, and the o u t s i d e 60° cone was cut at the base of t h i s t h r e a d . T h i s f i t t i n g was machined from s t a i n l e s s s t e e l bar, which had been d r i l l e d w i t h a t h r e e - e i g h t s h o l e t o a l l o w a s l i p f i t over the cup stem. 30. .VII.' OUTER SHELL (A) The outer s h e l l i s of heavy copper to r e s i s t s t r a i n s due to the vacuum i n s i d e , to overcome the buoyant f o r c e due to the l i q u i d I t d i s p l a c e s and to even out temperature g r a d i e n t s i n the hath l i q u i d . The i n s i d e of the outer s h e l l has been t i n n e d . The outer s h e l l i s made up of two p a r t s which are assembled by means of a f l a n g e c o n n e c t i o n . The f l a n g e j o i n t i s the f u l l Van Stone type w i t h the copper piened over to the f u l l width of the f l a n g e and supported by a brass r i n g on e i t h e r s i d e of the j o i n t . A f u l l gasket of o n e - s i x t y - f o u r t h i n c h Garlock packing dressed w i t h stopcock grease on e i t h e r s i d e was i n s e r t e d i n the j o i n t and the twelve s t e e l b o l t s around the f l a n g e were p u l l e d up evenly to secure the j o i n t . The assembled c a l o r i m e t e r was t e s t e d f o r l e a k s w i t h an i n t e r n a l p r e s s u r e of f o u r l b s . gauge of n i t r o g e n w i t h the c a l o r i m e t e r immersed i n water. The l e a d wire duct and vacuum tube i s a h a l f i n c h i n s i d e d i a . tube brought i n t o the. top of the s h e l l where i t i s s o l d e r e d . The upper end of t h i s tube c a r r i e s a b r a s s cup w i t h a r e c e s s e d mouth i n which a l u c i t e cap is'mounted. This cap i s d r i l l e d w i t h the r e q u i r e d number of h o l e s , one f o r each i n d i v i d u a l wire l e a d from the c a l o r i m e t e r . When a l l the l e a d s were p u l l e d through the l u c i t e cap the open space i n the cup above the cap was f l o o d e d w i t h p a r a f f i n to e f f e c t a s e a l . 31. (B) The groups of wires p a s s i n g through t h i s tube; i . e . , h e a t i n g l e a d s , thermometer l e a d s , and thermocouple groups, are separated from each other by macaroni i n s u l a t i o n to l e s s e n the chance of s h o r t s d e v e l o p i n g . There i s an e v a c u a t i o n branch a t t a c h e d to the l e a d wire j u s t below the cup. I t i s through t h i s branch that the e n t i r e c a v i t y i n the c a l o r i m e t e r e x c l u d i n g the cup and i t s vapour tube i s evacuated. There i s a 1 I n . i . d . heavy copper c a s i n g tube r i s i n g from the outer s h e l l cap, f l a n g e d at i t s upper end. T h i s f l a n g e serves to a l i g n the vapour tube and the c a l o r i m e t e r cup which i s threaded i n t o the lower end of the vapour tube, a x i a l l y with the outer s h e l l . 32. V I I I . BATH AND CIRCULATOR • The hath i s made from 16 ga. copper w i t h seams "brazed and hammered har d . The upper edge i s turned over ahout an i n c h to support the two h a l v e s of the top. The bottom i s rounded to prevent the form a t i o n o f c o l d spots through inadequate a g i t a t i o n . The h a t h i s supported and h e l d i n p l a c e on a heavy t a b l e by a l a y e r of i n s u l a t i o n about 2 i n . t h i c k which i s l a i d underneath the bat h and brought up i t s s i d e s to the upper edge.. This i n s u l a t i o n i s composed of asbestos paper which was pulped w i t h water and f o r t i f i e d w i t h cement to about a quarter of the dry weight of the asbe s t o s . A f t e r the i n s u l a t i o n was a p p l i e d , the water was d r i v e n out of the i n s u l a - . t i o n by warming the bat h on the i n s i d e w i t h a. 100 watt l i g h t globe f o r a week. The r e s u l t i n g compost i s bot h a good heat and e l e c t r i c a l i n s u l a t o r , p o s s e s s i n g c o n s i d e r a b l e r i g i d i t y . The two h a l v e s of the cover are s i m i l a r l y t r e a t e d . To i n s u r e p o s i t i v e c i r c u l a t i o n , a f o r c e d c i r c u l a t o r has been made and i n s t a l l e d . I t c o n s i s t s of a v e r t i c a l l e n g t h o f tube i n which a s h a f t c a r r y i n g f o u r p r o p e l l o r b l ades i s h e l d i n alignment by three b e a r i n g s . A tube s u p p l y i n g the f e e d . t o these p r o p e l l e r s draws the l i q u i d from around the v e r t i c a l c a s i n g tube from the dome of the c a l o r i m e t e r and the d e l i v e r y tube from the p r o p e l l o r s f o r c e s t h i s l i q u i d out at the base of the c a l o r i m e t e r s h e l l and down i n t o the bottom of the b a t h . I t w i l l be noted t h a t the rounded contours of the bat h and o f 33. the outer s h e l l of the c a l o r i m e t e r make f o r easy flow l i n e s of the c i r c u l a t e d l i q u i d which should r e s u l t i n few temperature g r a d i e n t s through the hath. The c i r c u l a t o r i s h e l d to the w a l l of the hath by two hands around i t s v e r t i c a l tube from which lugs are b o l t e d through the s h e l l of the bath, the b o l t s b e i n g made w a t e r t i g h t with neoprene gaskets. The c i r c u l a t o r i s d r i v e n by a \ h.p., t h r u s t - b e a r i n g motor d i r e c t - c o n n e c t e d t o the p r o p e l l o r s h a f t . The motor i s supported independently from a w a l l b r a c k e t above the bath to e l i m i n a t e as much v i b r a -t i o n as p o s s i b l e . Whatever temperature g r a d i e n t s should develop i n the bath would not be of gre a t consequence s i n c e the c a l o r i m e t e r s h e l l i s h e a v i l y c o n s t r u c t e d and made of copper and w i l l e f f e c t i v e l y l e v e l out such g r a d i e n t s b e f o r e they can have an e f f e c t on the i n n e r mechanism of the c a l o r i m e t e r . The c a l o r i m e t e r i s supported In the bath c e n t r a l l y from a l e n g t h of angle i r o n secured to v e r t i c a l p o s t s at each si d e of the t a b l e . I t . i s i n s u l a t e d from the angle i r o n by rubber shims. The vapour tube i s d i r e c t e d towards the open p a r t of the room f o r the f u t u r e attachment o f c o l d t r a p s and recep-t a c l e s , f o r measurements of heats of v a p o r i z a t i o n under vacuum or p r e s s u r e . 34. IX. SWITCHBOARD RHEOSTATS (A) The r h e o s t a t s are arranged so t h a t the c u r r e n t s p a s s i n g through the present s i x o p e r a t i n g h e a t e r s 'can he ad j u s t e d and h e l d t o a balance r e s u l t i n g i n a steady r a t e o f i n c r e a s e i n the temperature of the c a l o r i m e t e r . The d e t e r m i n a t i o n of the maximum r a t e of h e a t i n g i n the cup he a t e r has been d e s c r i b e d , and the o p e r a t i o n of the r h e o s t a t s i s i n accordance w i t h any r a t e of cup h e a t e r i n p u t between zero and t h i s maximum. Suppose the D.C. i n l e t i s on 100 v o l t s . The r h e o s t a t s i n s e r i e s with the cup heat e r a l l o w a range of amperage from .1 to 1 amp. through the cup h e a t e r , l e t us say t h a t the c u r r e n t d e s i r e d i s .5 amps. The c o i l heater i s 100 ohms, so set the r e s i s t a n c e i n s e r i e s to about 100 ohms and the cup c u r r e n t w i l l be .5 amps, (about). Keep t h i s cup c u r r e n t c o n s t a n t . A d j u s t the upper and lower envelope heaters to about .15 amps., the r i n g h e a t e r to .05 amps., the tempering r i n g to about .075 amps, and the stem guard to about .03 amps. A survey of the three galvanometers w i l l soon show which he a t e r s must be cut back or i n c r e a s e d . The w i r i n g between .rheostats allows c o n s i d e r a b l e l a t i t u d e i n a d j u s t i n g c u r r e n t s through a l l c o i l s . However, i f i t i s found that the range f o r any c o i l Is not great enough, cut down the 100 V D.C. source to say 40 V, and f o r a very slow r a t e of h e a t i n g to 6 V, r e s u l t i n g i n a lower l i m i t of in p u t f o r each h e a t e r . 35. (B) CAUTION. I would suggest that since the cup heater had to be wound on mica, with a low heat d i f f u s i v i t y , at no time should the cup heater current exceed 0.7 amps., and that the type of c o n s t r u c t i o n used i n the cup and elsewhere l i m i t s t h i s instrument to a maximum temperature of 150° C. and a t o t a l pressure from the i n s i d e of the cup outwards of not more.than at l b s . per sq. i n . , i n c l u d i n g the e f f e c t of vacuum w i t h i n the outer s h e l l . X. PLUNGER SEAL The plunger i s constructed of s t a i n l e s s s t e e l tube 18 N i . ^8 Cr., s i m i l a r to the cup stem. The tube i s stopped \ i n . from one end w i t h a p l u g of s i l v e r s o l d e r , and t h i s end was b u i l t up w i t h a bead of ordinary solder which was machined down to a f l a t plug which bears upon the c i r c u l a r edge ground on the cup stem. The. plunger tube was cut to l e n g t h a f t e r the cup had been I n s t a l l e d i n the vapour, tube and a brass flange was soldered at the r i g h t height on the upper end of the plunger to provide a broad r e c e i v i n g surface f o r the s e a l i n g diaphragm. Three a l i g n i n g r i n g s o.d. were soldered along the length of the plunger and ground to provide vapour passages. For l a t e r use I n heats of v a p o r i z a t i o n a h e a t i n g c o i l wj.ll have to be i n s e r t e d i n the plunger tube together 36. wi t h an o p e r a t i n g thermocouple which w i l l have t o be operated i n a manner analogous to thermocouple 16 p r e v i o u s l y d e s c r i b e d . A l s o an i n s i d e t h r e a d must be cut at the mouth of the tube to r e c e i v e a b o l t which a c t s to clamp the diaphragm down to i t s fla n g e s e a t . The b o l t w i l l be d r i l l e d to admit the thermo-couple and heater l e a d s , and the head of the b o l t must be pr o v i d e d w i t h lugs by which the plunger w i l l be r a i s e d and lowered as r e q u i r e d i n v a p o r i z a t i o n work, through a micrometer screw attachment supported from the diaphragm r e c e p t a c l e . In o p e r a t i o n f o r s p e c i f i c h e ats, the plunger i s p r e s s e d down upon the end of cup stem and the r e l a t i v e l y s o f t s o l d e r flows under the p r e s s u r e and seats around the stem to give a v a p o u r - t i g h t metal-to-metal s e a l . The weight of the plunger thus i n p l a c e i s equal to about 7 l b s . per sq. i n . p r e s s u r e above atmospheric on the cup.-37. XI. PROCEDURE FOR DISSEMBLING Twist the p e r f o r a t e d s u c t i o n r i n g of the c i r c u l a t o r to the side of the bath. Remove the clamps h o l d i n g the c a l o r i -meter to the angle i r o n and support the c a l o r i m e t e r t e m p o r a r i l y . Remove the angle i r o n from the wood p o s t s . The c a l o r i m e t e r can now be brought out of the b a t h i n a v e r t i c a l p o s i t i o n . I n v e r t the c a l o r i m e t e r and support i t on a t a b l e brought up to i t above the b a t h w i t h the diaphragm r e c e p t a c l e r e s t i n g on the t a b l e and the leads l e a v i n g the cup p a s s i n g down by the edge of the t a b l e . Support the c a l o r i m e t e r f i r m l y i n t h i s . p o s i t i o n w i t h clamps to the copper c a s i n g tube. Remove the f l a n g e b o l t s and pry t h e . f l a n g e a p a r t . Try to have the gasket remain when the outer s h e l l i s l i f t e d away: t h i s w i l l prevent the Inner edge of the gasket dragging a c r o s s thermocouples Nos. 12 and 13. Remove thermocouples 12 and 13 from beneath t h e i r c l i p s and allow them to hang f r e e . Cut the copper leads to the upper and lower envelope h e a t e r s : the lower envelope s e c t i o n , the envelope support r i n g and the upper envelope s e c t i o n can now be removed. F i r s t , remove the lower envelope s e c t i o n by grasp-i n g i t w i t h both hands and r o t a t i n g i t about an e i g h t h of an i n c h u n t i l i t s studs are f r e e of t h e i r s l o t s , then l i f t the s e c t i o n away. Remove the f o u r machine screws at the envelope support r i n g and remove the upper envelope s e c t i o n i n the manner d e s c r i b e d f o r the lower envelope s e c t i o n . The lower envelope s h i e l d can be removed i n a s i m i l a r manner when 38 . thermocouples 10 and 11 have been taken from t h e i r c l i p s . The lower c a l o r i m e t e r s h i e l d w i l l then be exposed. Before the c a l o r i m e t e r cup.can be removed a l l the thermocouple and heater l e a d j u n c t i o n s at the r e f e r e n c e r i n g must be cut and made f r e e . Then, the cone j o i n t can be opened by i n s e r t i n g a c r e s c e n t wrench between the f o u r hanger s t r a p s to the r e f e r e n c e b l o c k w i t h the jaws of the c r e s c e n t wrench pushed over the two f l a t s ground on the lower h a l f of the cone j o i n t f o r t h i s purpose. I t may be wise to cut and remove the thre a d b i n d i n g the l e a d s near thermocouple 6 on the stem to all o w b e t t e r access w i t h the wrench. I t w i l l r e q u i r e c o n s i d e r a b l e f o r c e to open t h i s j o i n g but once the cone s e a l i s broken i t should be easy to remove the cup by st e a d y i n g the cup s h i e l d with one hand and r o t a t i n g the stem w i t h the o t h e r . Do not as y e t attempt to remove the thermometers u n l e s s they alone must be s e r v i c e d . The r e f e r e n c e b l o c k can now be removed along w i t h the envelope s h i e l d cap. When a l l the leads have be drawn through t h e i r h o l e s on the upper envelope cap the f o u r b l o c k hanger b o l t s are removed and the upper envelope cap w i l l be f r e e . To r remove the vapour tube assembly cut the le a d s to the center and upper vapour h e a t e r s , remove the s i x b o l t s at the c a s i n g tube f l a n g e and then the vapour tube assembly can be f o r c e d out of the copper c a s i n g tube. The r e v e r s e procedure i s f o l l o w e d i n assembling the c a l o r i m e t e r . I f i t i s necessary t o remove the thermometers from t h e i r tubes, support the r i n g so that the thermometer lead s hang down, then f i l l the upper end of the tubes w i t h a s o l v e n t to cut any g l y p t a l f r o z e n between 39. housing and tube. Then f o r c e out the thermometers by a p p l y i n g pressure at the ev a c u a t i o n ends. MEASURFJIENTS OF HEAT OF VAPORIZATION" AND HEAT CAPACITY OF A NUMBER OF HYDROCARBONS BY NATHAN S . .OSBORNE* AND DEFOE C . .GUNNINGS MEASUREMENTS OF HEAT OF VAPORIZATION AND HEAT CAPACITY OF A NUMBER OF HYDROCARBONS by . Nathan S . Osborne and Defore C . G i n n i n g s P a r t I A CALORIMETER FOR MEASURING HEAT OF VAPORIZATION AND HEAT CAPACITY I , I n t r o d u c t i o n I I . Genera l d e s c r i p t i o n of method and a p p a r a t u s . I l l ; A p p a r a t u s . 1 . C a l o r i m e t e r s h e l l and i n c l u d e d p a r t s . 2 . T h e r m a l - p r o t e c t i n g e n c l o s u r e . 3». Vapor l i n e and t h r o t t l e v a l v e . 4. Thermometries i n s t a l l a t i o n and o t h e r w i r i n g * 5. A u x i l i a r y c o n t r o l f e a t u r e s . 6. Mass and power measuring i n s t i m m e n t s . I V . Genera l e v a l u a t i o n of the c a l o r i m e t e r . P a r t I I * HEAT OF VAPORIZATION OF FIFTY-NINE HYDROCARBONS I . I n t r o d u c t i o n . I I . Method. I l l * P r e p a r a t i o n of samples* I V . E x p e r i m e n t a l p r o c e d u r e . 1 . A c c o u n t i n g f o r mass, energy, and change i n s t a t e o f the sample* 2 . D e s c r i p t i o n of v a p o r i z a t i o n e x p e r i m e n t s . V . R e s u l t s o f v a p o r i z a t i o n e x p e r i m e n t s . 7 1 . Accuracy of r e s u l t s on heat of v a p o r i z a t i o n . P a r t I I I . HEAT CAPACITY OF TWELVE HYDROCARBONS. I . - I n t r o d u c t i o n . I I ; Method.. I I I . E x p e r i m e n t a l p r o c e d u r e . I V ; R e s u l t s of heat c a p a c i t y exper iments . V . D i s c u s s i o n of accuracy of heat c a p a c i t y r e s u l t s ; P a r t I V . REFERENCES 1. PART -I A CALORIMETER FOR MEASURING HEAT OF VAPORIZATION AND HEAT CAPACITY I . I n t r o d u c t i o n . The p r i n c i p a l purpose of the c a l o r i m e t e r d e s c r i b e d here was- to p r o v i d e f o r the s y s t e m a t i c d e t e r m i n a t i o n of the heat of v a p o r i z a t i o n of a number of samples of hydrocarbons w h i c h were a v a i l a b l e , ' m o s t l y i n a h i g h s t a t e of p u r i t y but i n s m a l l amounts. Such measurements on 59 hydrocarbons are d e s c r i b e d i n P a r t I I o f t h i s r e p o r t . A secondary purpose was t o p r o v i d e f o r d e t e r m i n a t i o n s of heat c a p a c i t y over a range o f t empera ture . Such measurements on 12 of the hydrocarbons are d e s c r i b e d i n P a r t I I I of t h i s r e p o r t . I I . Genera l D e s c r i p t i o n of method and a p p a r a t u s . The p r i n c i p l e s of the method used have been d e s c r i b e d i n p r e v i o u s p u b l i c a t i o n s ( l ) 1 , * Readers who are concerned o n l y w i t h the r e s u l t s of the measurements may choose to s k i p the d e t a i l s of P a r t I and pass at onoe to P a r t I I . 1 F i g u r e s i n b r a c k e t s i n d i c a t e the l i t e r a t u r e r e f e r e n c e s at the end of t h i s r e p o r t and t h e r e f o r e are not r e p e a t e d i n d e t a i l h e r e . The method was a p p l i e d p r e v i o u s l y ( 2 , 3 , 4 , ) to measurements on s a t u r a t e d water and steam from 0° to 3 7 4 ° C . The apparatus c o n s i s t s e s s e n t i a l l y of a c a l o r i m e t e r i n which a sample of the f l u i d may be so i s o l a t e d as to enable i t s amount, s t a t e and energy to be accounted f o r . The sample or a d e f i n i t e p a r t t h e r e o f may be made to pass e i t h e r through a r i s e of temperature or may be evaporated and withdrawn at a constant temperature w h i l e the accompanying g a i n or l o s s of energy i s de termined . The sample, p a r t l i q u i d and p a r t v a p o r , i s e n c l o s e d i n a m e t a l c a l o r i m e t e r s h e l l * An e l e o t r i c h e a t e r on t h i s s h e l l p r o v i d e s a means of adding measured energy to the s h e l l and c o n t e n t s . An o u t l e t tube w i t h v a l v e p r o v i d e s f o r f i l l i n g the c a l o r i m e t e r or w i t h d r a w i n g v a p o r . Detachable r e c e i v e r s , s u i t -ab le f o r w e i g h i n g are connected t o the o u t l e t tube to h o l d the samples of f l u i d t r a n s f e r r e d . F o r c o n f i n i n g the energy, the c a l o r i m e t e r i s w e l l i n s u l -a ted from e x t e r n a l sources of heat ; w h i l e i n o p e r a t i o n the temperature of an e n v e l o p i n g s h e l l i s kept c l o s e to t h a t of the c a l o r i m e t e r s h e l l . By o b s e r v i n g the temperature d i f f e r e n c e s , the s m a l l amount of heat w h i c h l e a k s to or from the c a l o r i m e t e r can be accounted f o r * I n the v a p o r i z a t i o n measurements, the process i s v i r t u -a l l y i s o t h e r m a l . Heat i s s u p p l i e d to evaporate a sample o f f l u i d whioh i s withdrawn from the c a l o r i m e t e r at a c o n t r o l l e d r a t e , c o l l e c t e d by condensa t ion , and weighed. From t h i s experiment there i s o b t a i n e d a va lue of a c h a r a c t e r i s t i c q u a n t i t y denoted by gamma, ^ , from which by t h e o r y ( l ) , the l a t e n t heat of v a p o r i z a t i o n can be o b t a i n e d by s u b t r a c t i n g another q u a n t i t y b e t a , (5 . I n a l g e b r a i c form* L = K - f t The q u a n t i t y ft has been shown t o be ft» Tu dP « L . u dT u ' - u where It i s heat of v a p o r i z a t i o n , u and u f are s p e c i f i c volumes o f s a t u r a t e d l i q u i d and v a p o r , r e s p e c t i v e l y , T a b s o l u t e temper-a t u r e , and dP/dT the vapor p r e s s u r e d e r i v a t i v e . I n the present d e t e r m i n a t i o n s ft i s so s m a l l t h a t approximate e v a l u a t i o n i s adequate f o r d e r i v a t i o n of v a l u e s of L . I n the heat c a p a c i t y exper iments , the c a l o r i m e t e r w i t h a sample of f l u i d i s heated over a measured temperature range . By making some experiments w i t h d i f f e r e n t amounts of f l u i d i t i s p o s s i b l e to account f o r the t a r e heat c a p a c i t y of the c a l o r -i m e t e r , and to o b t a i n the change of a q u a n t i t y denoted by a l p h a , oC , which I s a c h a r a c t e r i s t i c p r o p e r t y of the f l u i d . Theory shows t h a t the change i n oC d i f f e r s f rom the change i n e n t h a l p y , H , o f s a t u r a t e d f l u i d by the change i n (3 , men-t i o n e d above. I n a l g e b r a i c f o r m ; A H - AoC + A<3 A T 4 T A T I I I . Apparatus The e s s e n t i a l f e a t u r e s of the c a l o r i m e t e r may be e x p l a i n e d by r e f e r e n c e to the schematic d iagram, f i g . 1 . The meta l c a l o r i m e t e r s h e l l , G, p r o v i d e d w i t h an e l e c t r i c h e a t e r , H , i s 4* supported w i t h i n an i n s u l a t i n g space and i s surrounded by a thermal guard s h e l l or envelope, E , f o r c o n t r o l of heat l e a k . P r o v i s i o n i s made f o r t r a n s f e r o f f l u i d sample between the f l u i d c o n t a i n e r , F . C , and the c a l o r i m e t e r C by d i s t i l l a t i o n through the t h r o t t l e v a l v e , TV. The c a l o r i m e t e r s h e l l and envelope are enc losed w i t h i n an o u t e r s h e l l w i t h an o u t l e t tube used f o r both e v a c u a t i o n and e l e c t r i c l e a d s . The space w i t h i n t h i s s h e l l , and the. c a l o r i m e t e r and i t s connec t ions may be evacuated through l i n e s , VAC. The copper r e f e r e n c e b l o c k * R, p r o v i d e s a thermal c o n n e c t i o n between two p l a t i n u m r e s i s t a n c e thermometers, T, and the r e f e r e n c e j u n c t i o n s of thermoelements used f o r measuring the temperatures of p o i n t s on the c a l o r i m e t e r s h e l l and enve lope . I n u s e , the o u t e r s h e l l of t h i s c a l o r i m e t e r u n i t was immersed i n a water b a t h f o r c o n t r o l of surrounding tempera ture . The c a l o r i m e t e r and e s s e n t i a l p a r t s are shown i n d e t a i l i n the s c a l e drawing* F i g . &3. 1 . C a l o r i m e t e r s h e l l and i n c l u d e d p a r t s * The c a l o r i m e t e r s h e l l shown at C i s a d o u b l e - w a l l e d u n i t . The i n n e r s h e l l serves t o c o n t a i n the sample* The o u t e r s h e l l * a t t a c h e d to the p e r i p h e r y of the i n n e r s h e l l a t A i s a thermal s h i e l d which g i v e s the c a l o r i m e t e r a n e a r l y i s o t h e r m a l s u r f a c e r e g a r d l e s s of temperature g r a d i e n t s i n the i n n e r s h e l l * T h i s o u t e r s h e l l i s made of copper 0 . 1 mm t h i c k . The i n n e r s h e l l i s made w i t h a c y l i n d r i c a l s e c t i o n of 0.5 mm brass w i t h rounded end caps of spun b r a s s . This s h e l l i s put t o g e t h e r w i t h s o f t s o l d e r * the end caps f i t t i n g i n t o a s h a l l o w recess i n the 5 . c y l i n d e r ends and the t h i n c y l i n d e r ends spun down over the caps f o r s t r e n g t h . The o u t e r sur face of the i n n e r s h e l l and b o t h s u r f a c e s of the o u t e r s h e l l are g o l d - p l a t e d and p o l i s h e d t o minimize heat t r a n s f e r by r a d i a t i o n . Heat t r a n s f e r between these s h e l l s by gaseous conduct ion i s e s s e n t i a l l y e l i m i n a t e d by e v a c u a t i o n . The c a l o r i m e t e r h e a t e r , H ^ * i s a 100«*ohm r e s i s t o r of #34 constantan w i r e , i n s u l a t e d w i t h f i b r e g l a s s and wound over a s t r i p of t h i n mica cemented t o the b r a s s s h e l l by g l y p t a l l a c q u e r . On top of t h i s w i n d i n g i s cemented another t h i n mica s t r i p covered by a copper sheath whioh i s spun down on b o t h s i d e s of the w i n d i n g and s o l d e r e d to the b r a s s s h e l l . T h i s sheath not o n l y presses the h e a t e r element i n t o good thermal contact w i t h the b r a s s s h e l l but a l s o conducts back to the b r a s s s h e l l the heat which i t r e c e i v e s f rom the hea ter * Leads of 0 . 4 mm copper w i r e I n s u l a t e d w i t h enamel and s i l k are brought out from the copper sheath between mica s t r i p s * The i n t e r i o r of the c a l o r i m e t e r s h e l l i s n e a r l y f i l l e d w i t h a c e l l u l a r system of copper , f o r the purpose of prompt ing the r a p i d d i s t r i b u t i o n of heat* This tends to a v o i d e x c e s s i v e thermal g r a d i e n t s and l a g of temperature e q u a l i z a t i o n . T h i s heat d i s t r i b u t i n g system c o n s i s t s of v e r t i c a l sheets of copper ( 0 . 1 mm t h i c k ) arranged as shown i n the c r o s s s e c t i o n F i g . / 2 . There are t h i r t y sheets o f t i n - c o a t e d copper* out to shape and bent so t h a t when spaced and a t t a c h e d by t i n s o l d e r to the i n n e r sur face of the b r a s s c y l i n d e r , they form 60 r a d i a l p l a t e s , 30 of whioh extend to the c e n t r a l v o i d of 5 mm d i a m e t e r , 6. and 30 more w h i c h extend to a diameter of 25 mm. At the bottom these p l a t e s extend c l o s e to the bottom c a p , w h i l e at the top they extend o n l y to the l e v e l of the top j o i n t l e a v i n g a s m a l l open space under the top c a p . W i t h t h i s system of p l a t e s , no p a r t of the l i q u i d sample i n the c a l o r i m e t e r i s more remote than about 2 or 3 mm from a c o n d u c t i n g m e t a l p a r t . D i r e c t l y on the l e v e l top o f the copper p l a t e s i s a b a f f l e (3) of s i l v e r w i r e gauze, 100 mesh to the i n c h , i n the form of a r i n g ex tending to the o u t e r c y l i n d r i c a l w a l l and cut out at c e n t e r to 24 mm diameter , and spaced to a l l o w f r e e f l o w of vapor upward i n the c e n t e r . Another b a f f l e of c o n i c a l shape r e s t s w i t h v e r t e x a t c e n t e r and base a g a i n s t the top cap at a diameter of about 3 cm. At t h i s p e r i m e t e r , f o u r spaces are l e f t f o r vapor f l o w i n toward the outf low, tube i n c e n t e r of top cap. The purpose of these two b a f f l e s i s t o i n t e r c e p t any drops of l i q u i d w h i c h might be p r o j e c t e d d i r e c t l y i n t o the vapor o u t f l o w tube by a c t i v e b o i l i n g , should i t o c c u r , " They a l s o p r o b a b l y f a v o r the tempering of the vapor t o the tempera-t u r e of the top p a r t of the c a l o r i m e t e r . 2 . T h e r m a l - p r o t e c t i n g e n c l o s u r e The three obvious and f a m i l i a r means f o r a v o i d i n g the g a i n or l o s s of unmeasured heat were p r o v i d e d by use of a p r o t e c t i n g enc losure f o r the c a l o r i m e t e r . These t h r e e means are thermal i n s u l a t i o n , thermal c o n t r o l of enve lope , and temperature-survey p r o v i s i o n . Thermal i n s u l a t i o n was p r o v i d e d by e v a c u a t i o n of the space between c a l o r i m e t e r w a l l and envelope w a l l j and by g o l d p l a t i n g 7 . and. p o l i s h i n g the w a l l s u r f a c e s to g i v e low e m m i s s i v i t y . A l s o the unavoidab le s o l i d , connect ions between the two elements such as e l e c t r i c l e a d w i r e s were kept to t o l e r a b l e p r o p o r t i o n s . Thermal c o n t r o l of the envelope was provided, by an e l e c -t r i c h e a t e r , R"2, on the o u t e r w a l l of the d o u b l e - w a l l e d enve-l o p e , and by survey thermoelements f o r o b s e r v i n g the tempera-t u r e d i f f e r e n c e s . The a c t u a l c o n t r o l was e f f e c t e d e i t h e r manual ly by an observer of the thermoelement i n d i c a t i o n s or by the automatic means to be d e s c r i b e d l a t e r . The i n n e r guard w a l l of t h e . e n v e l o p e , which was made s i m i l a r to the o u t e r s h i e l d w a l l of the c a l o r i m e t e r , was f o r the same purpose , i . e . to a v o i d too g r e a t thermal g r a d i e n t s i n the opposed h e a t - l e a k s u r f a c e s . From the p e r i p h e r y a t D of the enve lope , an e x t e n s i o n w i t h cap, N , p r o v i d e d a t h e r m a l l y - c o n t r o l l e d space s u i t a b l e f o r the r e f e r e n c e b l o c k , R, and a l s o f o r the o u t f l o w t u b e , and t h r o t t l e v a l v e , TV. The c y l i n d r i c a l p a r t of t h i s e x t e n -s i o n , i s p r o v i d e d w i t h an e l e c t r i c h e a t i n g c o i l f o r temperature c o n t r o l . The c a l o r i m e t e r s h e l l i s supported by the o u t f l o w tube which i s a t t a c h e d to the c e n t e r of the o u t e r cap. This tube passes w i t h o u t contact through the envelope and through the deck, N , which i s the upper boundary of the p r o t e c t i n g e n d o s u r e . 3 . Vapor l i n e and t h r o t t l e v a l v e . The s e c t i o n of the o u t f l o w tube between the c a l o r i m e t e r and the seat of the t h r o t t l e v a l v e i s o f s t a i n l e s s s t e e l (18 N i — 8 Or) h a v i n g an i n s i d e diameter of 3 . 5 mm and a w a l l 8 . thickness of 0 . 2 5 mm. The top of this steel tube was l e f t thicker and was machined in the form of a circular edge, sharply beveled to about a 90° angle. This beveled edge formed the seat of the throttle valve, which was closed or opened by the seating or withdrawal of the valve stem end. This consisted of a thin coating of t i n on the f l a t silver disc normal to the axis of the valve stem. Motion of the valve stem through the tubular stem casing of copper-nickel was controlled by a specially-designed mechan-ism. This mechanism i s the identical one previously used i n apparatus for measurements on water (4). The essential difference between the previous valve assembly and present one i s in the length of the valve stem. In the former the portion of the stem below the flexible d i -aphragm was but 5 mm, the entire valve and mechanism being kept at the temperature of the calorimeter. In the present design, intended to be useful at sub-atmospheric temperatures and within an evacuated space, the length was increased to about 30 cm by using a section of copper-nickel tube, 5 . 3 mm outside diameter, 0 . 3 mm wall thickness; as an extension. The ends of this tubular section were formed by pressing into a triangular fluting or Y shape; For the purpose of exact centering of the stem on i t s seat, the lower fluted section was lathe turned to a slip f i t in the section of the tubular sleeve just above the valve seat; The end was recessed to receive the silver disk for the stem end. At the top end a brass female-threaded bushing was f i t t e d to engage the male screw threaded, stud, extending through the diaphragm. I n order to u t i l i z e the i n s i d e of the t u b u l a r stem as f l o w space* the tube was p e r f o r a t e d at each end by 3 h o l e s where the Y s e c t i o n j o i n e d the c i r c u l a r p a r t . The c y l i n d r i c a l c e l l at the top of the v a l v e - s t e m s leeve i s capped at top by a f l e x i b l e cor rugated copper diaphragm clamped t i g h t l y to the upper r i m of the c e l l , which was s l i g h t l y recessed to center the diaphragm. The clamp, h e l d down by 12 screws i s beve led to an edge where i t bears, on the copper dia-? phragnu A g a s - t i g h t s e a l a t t h i s r i s i n g contac t i s o b t a i n e d by a t h i n f i l m of s top-cock grease be fore a s s e m b l i n g . The mechanism f o r moving the v a l v e stem i n c l u d e s two l e v e r s a c t i n g a x i a l l y on the stem o u t s i d e the diaphragm." One l e v e r t h r u s t s a s t r u t a g a i n s t the stem f o r c l o s i n g , and the o ther l i f t s i t by a s t i r r u p f o r o p e n i n g . These l e v e r s ac t on k n i f e edges as f u l c r u m s to a v o i d i r r e g u l a r i t y i n t h e i r m o t i o n . The c l o s i n g l e v e r i s ac tua ted by a s p r i n g which* n o t o n l y p r e -vents any b a c k l a s h , but keeps a steady moderate f o r c e a g a i n s t the seat of the v a l v e when c l o s e d * The opening l e v e r , w i t h a r e d u c t i o n of mot ion of 4 to 1 i s operated by a screw w i t h a p i t c h of 32 threads p e r i n c h . The shaf t of t h i s sorew extends up through a u n i v e r s a l j o i n t to a grooved p u l l e y and i s d r i v e n by remote c o n t r o l w i t h a w i r e b e l t f rom a s m a l l p u l l e y over the o b s e r v i n g bench. A s h a f t f rom t h i s p u l l e y extends down t o a hand wheel w i t h a d j u s t a b l e l e v e r at the observers hand* T h i s e n t i r e t r a i n of mechanism g i v e s a r e d u c t i o n of 3 0 , 0 0 0 to 1 from end of hand l e v e r t o v a l v e stem w i t h no pereeptab le back-10. lash In the operation of the valve. It i s believed, that this fine control contributed substantially to the consistency of the experimental results. A heating c o i l , shown at i n Fig. 2 was wound directly on the casing of the throttle valve to permit control of the -temperature of the valve and outlet tube. The purpose of this control was to avoid error due to condensation. The outlet tube extends vertically up from the valve and out horizontally from the diaphragm c e l l . From there i t leads through a metal tube to a glass stopcock, beyond which a metal union provides for the attachment of one of several Pyrex-glass containers for holding a sample of f l u i d . A side tube permits evacuation of the vapor l i n e . The glass con-tainers of about 225 cm3 capacity are provided with unions and stopcocks so they can be detached and weighed for deter-mining the amounts of samples. 4. Thermometrie installation and other wiring. Platinum resistance thermometers supplemented by thermo-elements were used i n the control and measurement of tempera-tures. One of the two resistance thermometers placed at M in the copper reference block determines a reference datum on the International Temperature Scale.* from which small temper-ature differences to the calorimeter shell or other points are measured by means of thermoelements. Thermoelements are also used differentially for the survey of temperature dis-tribution and for regulation of the calorimetric processes. 1 1 . The advantages of t h i s combinat ion of r e s i s t a n c e thermo-meter and thermoelement i n c a l o r i m e t r y have been r e c o g n i z e d and used i n t h i s l a b o r a t o r y f o r a q u a r t e r of a c e n t u r y . The r e l i a b i l i t y of the modern p l a t i n u m r e s i s t a n c e thermometer to reproduce the i n t e r n a t i o n a l s c a l e j u s t i f i e s i t s use to e s t a -b l i s h the r e f e r e n c e datum of temperature . On the o ther hand, the thermoelement i s i d e a l f o r supplementing the r e s i s t a n c e thermometer i n the measurement of s m a l l temperature d i f f e r e n c e s where u n c e r t a i n t y of c a l i b r a t i o n and homogeneity o f w i r e may be n e g l i g i b l e . The thermoelement has the advantages of l o w e r heat capacity" , b e t t e r r e s p o n s i v e n e s s , g r e a t e r a d a p t a b i l i t y to l i m i t e d space and to d i f f i c u l t y a c c e s s i b l e p o i n t s , and the p o s s i b i l i t y of m u l t i p l e combinat ions t o g i v e i n t e g r a t i o n of temperatures , more s e n s i t i v i t y , or measurement of temperature d i f f e r e n c e s . The use of a w e l l - c o n d u c t i n g - s u i t a b l y - s h a p e d mass of m e t a l as a r e f e r e n c e b l o c k i s a method of u t i l i z i n g these v i r t u e s , where the d e s i r e f o r p r e c i s i o n or r e l i a b i l i t y outweighs the disadvantage of g r e a t e r c o m p l e x i t y of c o n s t r u c t i o n and accessory equipment. The r e f e r e n c e b l o c k , R, i s l o c a t e d i n the space j u s t above the c a l o r i m e t e r and envelope, where i t i s convenient f o r w i r i n g , and i s o l a t e d from outer causes so t h a t i t s temperature i s sub-j e c t t o c o n t r o l . The purpose of the r e f e r e n c e b l o c k b e s i d e s f u r n i s h i n g a c l o s e thermal c o n n e c t i o n between the s tandard thermometer and the temperature measuring thermoelements, i s a l s o to b r i n g a l l the r e f e r e n c e j u n c t i o n s t o a common temper-a ture so t h a t they may be used d i f f e r e n t i a l l y . T h i s b l o c k i s 12. oopper i n the form of a horizontal r i n g of rectangular section, to which are soldered, two heavy-walled copper tubes f i t t i n g i n grooves (M) cut i n the lower face of the r i n g ; These tubes serve as resistance thermometer receptacles and are reamed to a close s l i p f i t f o r the c y l i n d r i c a l platinum cases of the two resistance thermometers. A shallow groove was cut i n the middle of the outer c y l i n d r i c a l face of the r i n g to receive a heating c o i l , H^ , f o r temperature contr o l . The outer c y l i n d r i -c a l face of the rin g i s used f o r attaching reference junctions of the thermoelements and also attachments f o r the leads to thermoelements and resistance thermometers. These attachments besides f i x i n g the wires i n po s i t i o n , are f o r intercepting heat conducted along the leads and w i l l be referred to as " t i e -downs". The two platinum resistance thermometersj one of which was used as working standard, and the other f o r a c a l i b r a t i o n check, were of the four-lead potential-therminal type described by C. H. Meyers (j>). The windings were of pure platinum wound on a mica cross. The wire'was 0 . 1 mm diameter and was f i r s t - v; wound i n the notched mica cross. The thermometers were encased i n tubes of platinum of 6 . 3 5 mm outside diameter and about 0 . 2 mm thickness, which f i t t e d c l o s e l y into the receptacles i n the reference block. The cases were l i n e d with mica 0 * 0 1 mm thick to guard against possible e l e c t r i c a l contact with the platinum wire. The four lead wires were brought through holes i n the shallow re-entrant platinum cap, from whioh they were insulated 13. by small beads of fused glass. The caps, which f i t t e d closely into the casing were sealed to i t by electric welding, thus leaving the outer surface clear for insertion into the recep-tacle, with only the leads projecting out. The opposite end of the thermometer case was prepared for sealing i n a f i l l i n g of helium gas by spinning down the end to a diameter of about 2.5 mm where a short section of glass tubing was fused on. This could be drawn out and f i n a l l y sealed. The thermometers were annealed i n a i r at about 475°C for about 8 hours. The calibration was made i n terms of the International Temperature Scale by using the fixed points of ice and steam and an interoomparison at 30°C with a primary standard resis-tance thermometer.• The thermometers f u l f i l l e d the requirements of the international scale and were selected from a group of 4 for their consistency. Each had a resistance of about 40 ohms at the ioe points. The 16 thermoelements are a l l wired with leads to the outside so that each thermoelement may be used either separ-ately or i n desireable combinations* The positions of the measuring junctions are indicated i n Fig. The group J l to J5 i n series i s used to measure the ay/erage temperature of the calorimeter shell relative to the reference block when the calorimeter i s i n equilibrium at the beginning or end of an experiment. Simultaneous readings of the resistance thermometer i n the reference block complete the temperature observation* The thermoelements Jo* J7* and J8 are located on the •'A 14. vapor l i n e a l o n g w h i c h occurs a l l the heat l e a k by c o n d u c t i o n t o and from the c a l o r i m e t e r s h e l l . The combinat ion J7 a g a i n s t J5 i s used t o measure t h i s heat l e a k , w h i l e another d u p l i c a t e combinat ion J7» a g a i n s t J5» i s used to a u t o m a t i c a l l y r e g u l a t e t h i s heat f l o w . The thermoelements J9 and J10 are l o c a t e d on the o u t e r c a l o r i m e t e r s h e l l and the i n n e r envelope s h e l l ; r e s p e c t i v e l y , and are used d i f f e r e n t i a l l y to measure heat l e a k by r a d i a t i o n between these two s u r f a c e s . Heat l e a k by gaseous c o n d u c t i o n and c o n v e c t i o n was e l i m i n a t e d by e v a c u a t i o n . A d u p l i c a t e thermoelement c o m b i n a t i o n , J9* a g a i n s t JT0* , i s used to a u t o -m a t i c a l l y r e g u l a t e t h i s heat l e a k by r a d i a t i o n . These thermo-elements were c a r e f u l l y l o c a t e d so t h a t they i n d i c a t e d as n e a r l y as p o s s i b l e the average temperatures o f t h e i r r e s p e c t i v e s h e l l s under a l l c o n d i t i o n s . Temperature g r a d i e n t s i n the s h e l l s had n e g l i g i b l e e f f e c t on any heat l e a k a c c o u n t i n g . The thermoelements J l l , J12 , and JIJJ are l o c a t e d on the upper p a r t of the envelope s h e l l and are observed i n order to p r o p e r l y d i s t r i b u t e the heat among the h e a t e r s on the envelope s h e l l ; The thermoelement J14 i s l o c a t e d i n t h e r m a l contac t w i t h the o u t e r copper c o n t a i n e r and i s d i f f e r e n t from the o ther thermoelements i n t h a t i t has i t s r e f e r e n c e j u n c t i o n a t the temperature of J 1 3 so t h a t i t r e a l l y reads the temperature d i f f e r e n c e between J14 and J13&. I t i s used i n t h e r e g u l a t i o n of the temperature of the b a t h surrounding the o u t e r c a s e . The u s u a l type of thermoelement j u n c t i o n was made on a s m a l l sheet of copper , e i t h e r shaped as a c i r c u l a r washer 15. with a radial tag, or as a rectangular terminal, The two wire joined, were soldered close together to the terminal i n the manner described in previous report ( 3 )• The rectangular type was used for measuring junctions on calorimeter and envelope, and was attached thermally by inserting between mica insulation and cemented with lacquer under small copper clips soldered to the surface* The washer type was attached by clamping with a screw stud and nut between thin mica washers, either to the reference block or to the two tempering rings, yet to be des-cribed, for intercepting heat conducted from outside down the leads* A third type of junction and attachment was used for junctions J5, J 5 1 , J6, J7, J 7 f and J8. In this type; the ends of the two wires were soldered together, and the wires rein-sulated with s i l k , and bound and lacquered to the tube for several turns away from the junction to insure adequate thermal contact. The washer type of tie-down terminals was used for anchor-ing the thermometer leads to the reference block and for ther-mal tie-downs at three additional zones including the tempering rings. Four horizontal zones of thermal attachment of thermo-elements, thermometer leads and heater leads are designated i n Fig. 3 as F, G, K, and L» Zones F and G are located on the reference block, and have 30 screw studs for thermal " t i e -downs" on each zone. Zone K i s located on the copper tempering ring which i s thermally integral with the upper cap of the 16. envelope e x t e n s i o n . This r i n g has a h e a t e r , H 4 , f o r t e m p e r -a ture c o n t r o l , and hears 40 thermal t i e - d o w n s . Zone I i s another tempering r i n g which i s t h e r m a l l y i n t e g r a l w i t h the top cap of the outer s h e l l . T h i s a l s o has 40 thermal t i e - d o w n s . Four mica s t r u t s form the s u p p o r t i n g attachment between r i n g K and r i n g L , and these s t r u t s c a r r y the e n t i r e envelope s t r u c t u r e r i g i d l y , w i t h n e g l i g i b l e heat t r a n s f e r . The r e f e r e n c e b l o c k i s c a r r i e d between e i g h t copper-n i c k e l l e g s f o u r above and f o u r be low. These l e g s are 0 . 8 mm t h i c k and 3*4 mm w i d e , and form a n e a r - r i g i d support f o r the envelope s h e l l be low. The envelope e x t e n s i o n above J> may be lowered f o r access to the w i r i n g space about the r e f e r e n c e b l o c k . The w i r e s l e a d i n g from the re fe rence b l o c k , Zone Qt to the tempering r i n g , Zone K , pass through s l o t s i n the outer r i m of the c a p . Leading from the t i e - d o w n s on the tempering r i n g , zone K , the w i r e s pass through the gap between the two r i n g s K and L , and thence out through the l e a d - w i r e d u c t , P . W i t h i n t h i s duct the w i r e s , i n c l u d i n g thermoelementi thermometer, and h e a t e r l e a d s are grouped i n t o compact bundles w i t h hea ter l e a d s separate f rom the o thers to l e s s e n danger of e l e c t r i c l e a k a g e . At the top of t h i s duct the w i r e s pass out through s m a l l h o l e s i n a l e u c i t e cap (Q) w h i c h i s sea led w i t h a r e s i n l a c q u e r , so the e n t i r e i n t e r i o r space may be evacuated through the s i d e tube from the l e a d d u c t . The system o f ' s e v e r a l zones of t i e - d o w n s f o r the v a t i o u s e l e c t r i c a l l e a d w i r e s was designed to i n t e r c e p t heat l e a k 1 7 . a l o n g these w i r e s to p r o t e c t the thermometric elements from extraneous lead, c o n d u c t i o n e f f e c t s . The s m a l l c o n d u c t i o n of the e l e c t r i c a l l e a d s f rom the c a l o r i m e t e r s h e l l was accounted f o r by t i e i n g them t h e r m a l l y to the vapor l i n e between thermo-elements J 7 and Jj>, and i n c l u d i n g t h e i r c o n d u c t i o n w i t h the meta l tube conduct ion as measured by J 7 a g a i n s t J 5 . Outs ide the c a l o r i m e t e r the l e a d s were brought over t o the o b s e r v i n g s t a t i o n where s p e c i a l l y b u i l t a l l - c o p p e r d i s t r i b u -t i n g switches p r o v i d e d f o r v a r i o u s combinat ions of thermoele -ments f o r the s e v e r a l f u n c t i o n s mentioned above. By manipu-l a t i o n of these s w i t c h e s , the observer c o u l d q u i c k l y s h i f t from one to another combinat ion w i t h o n l y d e l a y f o r galvano? meter response . The emf T s of the thermoelements were measured on a Wenner potent iometer and thermoelement c a l i b r a t i o n e r r o r s were n e g l i g i b l e . The f i v e thermoelements; JT to JJ?, used t o measure the temperature of the c a l o r i m e t e r s h e l l , were c a l i b r a t e d i n p l a c e by comparison w i t h the r e s i s t a n c e thermometer i n the r e f e r e n c e b l o c k . T h i s procedure was f i r s t to observe the thermometer and thermoelements, when the r e f e r e n c e b l o c k temperature was v e r y c l o s e to t h a t of the c a l o r i m e t e r . The r e f e r e n c e b l o c k was then heated f o r a few seconds, w h i l e the c a l o r i m e t e r temperature remained v i r t u a l l y c o n s t a n t , and the o b s e r v a t i o n s were r e p e a t e d . The change i n emf of the thermo-elements was thus g i v e n i n terms of the temperature s c a l e . No evidence was found t h a t the c a l i b r a t i o n f a c t o r of any of 18 the other similar thermoelements differed, from this one, but even had they differed, the manner of use avoided any s i g n i f i -cant error due to this cause since the heat leak factors were experimentally determined and th£ thermoelement readings were calibrated directly i n terms of power. The resistances of. the two platinum thermometers were measured with a Mueller bridge (6) and were calibrated previous ibo the installation i n the reference block. Inter comparisons of the two thermometers made at several times during the progress of the measurements showed that no significant relative change had occurred. Small changes in the thermometers would have caused only insignificant effects on the calorimetric results. Use of a commutator with normal (N) and reverse (R) posi-tions adapts the bridge for measuring the resistance between the branch points of a four-terminal resistance thermometer. A bridge current of 0.00j> amp was used, half of which passed through the thermometer. A snap reversing switch for the bridge current served to account for galvanometer zero d r i f t , and to double the sensitivity. 5. Auxiliary, Control Features. One very important control feature has already been des-cribed, i.e. the vapor throttle valve. This i s adjusted manu-all y by the operator to open or shut the vapor line and to regulate the evaporation temperature. Other control devices are used i n the various heating circuits some of which are manual, some automatic, and some 19. p a r t l y each. One o f the l a t t e r type i s the main s w i t c h i n the c a l o r i m e t e r h e a t e r c i r c u i t . T h i s i s a d o u b l e - p o l e double - throw s w i t c h , which i s thrown e i t h e r way by a s p r i n g tensed by a hand l e v e r * The s w i t c h i s r e l e a s e d f o r q u i c k throw by a t r i g g e r p u l l e d by the e l e c t r i c seconds s i g n a l from the s tandard c l o c k . A key i n the c l o c k c i r c u i t a l l o w s the opera tor t o choose the p a r t i c u l a r second s i g n a l to s t a r t or stop the c a l o r i m e t e r h e a t i n g c u r r e n t . The h e a t i n g p e r i o d are n o r m a l l y i n t e g r a l numbers o f m i n u t e s . The h e a t i n g c i r c u i t s f o r c o n t r o l of the temperatures of the envelope and envelope e x t e n s i o n are operated by b o t h manual and automatic c o n t r o l . The purpose of t h i s d u a l p r o v i s i o n i s to s i m p l i f y the exper imenta l m a n i p u l a t i o n and p r o v i d e b e t t e r c o n t r o l w i t h l e s s of the o p e r a t o r * s a t t e n t i o n . The h e a t i n g c o i l s are s u b d i v i d e d i n t o s e c t i o n s so l o c a t e d on the s h e l l s t h a t one group may be operated manual ly to produce a d e s i r e d change i n temperature of the e n t i r e envelope system. Another group; operated by automat ic c o n t r o l , r e g u l a t e s the temperature d i f f e r e n c e between the c a l o r i m e t e r and envelope to keep the heat l e a k t o a s m a l l steady r a t e , - e i t h e r when the temperature i s steady or changing* > This automatic c o n t r o l i s ac tua ted by the emf of thermo-element J 9 t - J 1 0 t ; p r e v i o u s l y i n d i c a t e d . T h i s emf i n combinat ion w i t h a s imple p o t e n t i o m e t e r c i r c u i t , galvanometer , p h o t o e l e c t r i c c e l l and a m p l i f i e r , c o n t i n u o u s l y r e g u l a t e s the h e a t i n g c u r r e n t to c o n t r o l the temperature d i f f e r e n c e . The temperature g r a d i -ent a l o n g the vapor tube i s a u t o m a t i c a l l y r e g u l a t e d to a 20. desired value by a similar circuit actuated by the emf or ther-moelement 7 « « 5 » . Each heater i s connected directly in the plate circuit of two type - 25L.6 electron tubes i n parallel, which are i n turn driven by type - 38 electron tubes which are controlled by the photoelectric cell-galvanometer combination.' The advantage of this system i s that the control of the current in the heaters i s continuous instead, of on-and-off. The auto-matic controls could be set to regulate the temperatures of the envelope and throttle at any desired temperature difference from the calorimeter regardless of any changes i n the tempera-ture of the calorimeter, such as i n heat capacity experiments. The heating c o i l on the reference block and the one used in the water bath are both manually controlled. 6 . Measurement of Mass and Electric Energy A sensitive balance of a capacity of 2 kg with closed cabinet below, i n which containers, dummies and counterpoises were suspended, was used for weighing the samples. Calibrated platinum-plated brass weights were used. A Wolff-Diesselhorst potentiometer was used for measure-ments of current and potential drop in the calorimeter heater* These data with the time as furnished by the Rieffler standard clock determined.the electric energy* A 0.1-ohm four-terminal resistor i n series with the heater was used for the current measurement and a 1,000 to 1 ratio volt box for the potential drop. The potential drop was measured by two leads which join, the current leads at the zone K ( f i g . 2). The heat developed 2 1 . i n the c u r r e n t l e a d s between the c a l o r i m e t e r s h e l l and the p o t e n t i a l l e a d s , was accounted f o r by c a l c u l a t i o n , knowing the r e s i s t a n c e of the l e a d s and assuming an a r b i t r a r y c a l o r i m e t e r boundary near thermoelement J^ * T h i s c o r r e c t i o n was es t imated as 0.027fo and was b e l i e v e d to i n t r o d u c e no a p p r e c i a b l e u n c e r -t a i n t y i n the r e s u l t s . I f the c a l o r i m e t e r boundary had been taken at Jq or J ^ , i n s t e a d of at the maximum d i f f e r e n c e i n the c o r r e c t i o n would have been o n l y 0 . 0 0 6 % . A l l e l e c t r i c a l measuring ins t ruments were c a r e f u l l y c a l i b r a t e d . I V . Genera l E v a l u a t i o n o f the C a l o r i m e t e r . The c a l o r i m e t e r was designed m a i n l y f o r measuring heats of v a p o r i z a t i o n of s m a l l amounts of hydrocarbons , and i n c i d e n t l y f o r measuring l i q u i d heat c a p a c i t i e s . I t was found p o s s i b l e to make accurate measurements of heat o f v a p o r i z a t i o n on a few grams of m a t e r i a l . I n o ther words, the v a p o r i z a t i o n experiments c o u l d proceed u n t i l the c a l o r i m e t e r was p r a c t i c a l l y d r y . T h i s was the r e s u l t of the e f f e c t i v e heat d i s t r i b u t i n g system i n the c a l o r i m e t e r and the i s o t h e r m a l s h i e l d s on the c a l o r i m e t e r and envelope which made heat l e a k e v a l u a t i o n p r a c t i c a l l y i n d e -pendent of any temperature g r a d i e n t s on the main p a r t of the c a l o r i m e t e r or on the enve lope . I t i s b e l i e v e d t h a t the e l e c -t r o n i c automatic c o n t r o l s on the envelope and t h r o t t l e tempera-t u r e s , e f f e c t i v e i n a l l types of exper iments , were a g r e a t h e l p i n the m a n i p u l a t i o n of the a p p a r a t u s . 22. The authors w i s h to acknowledge the c o o p e r a t i o n of H. F . St imson of t h i s Bureau i n the d e s i g h of the c a l o r i m e t e r d e s c r i b e d i n t h i s p a p e r . PART I I HEAT OF VAPORIZATION OF FIFTY-NINE HYDROCARBONS I . I n t r o d u c t i o n I n the s c i e n t i f i c and t e c h n o l o g i c a l c o n s i d e r a t i o n o f chemica l r e a c t i o n s and processes i n v o l v i n g substances i n b o t h the l i q u i d and gaseous s t a t e s , the heat o f v a p o r i z a t i o n i s a necessary p r o p e r t y . W i t h i n the pas t few y e a r s ; hydrocarbons have become important components of manufac tur ing processes i n the p e t r o l e u m , r u b b e r , and chemica l i n d u s t r i e s . U h f o r t u n -a t e l y ; the e x i s t i n g da ta on the heats o f v a p o r i z a t i o n of hydro' carbons are l i m i t e d t o a r e l a t i v e l y s m a l l number of compounds. There became a v a i l a b l e a t t h i s Bureau r e c e n t l y b o t h a new c a l o r i m e t r i o apparatus s u i t a b l e f o r measuring heats of v a p o r i -z a t i o n and a c o n s i d e r a b l e number of hydrocarbons of adequate p u r i t y . I I . Method I n the v a p o r i z a t i o n exper iments ; the measured heat was s u p p l i e d e l e c t r i c a l l y t o evaporate l i q u i d ; w h i l e Vapor was withdrawn at a r a t e which was c o n t r o l l e d manual ly to keep a constant temperature of e v a p o r a t i o n ; The energy added per u n i t mass removed as v a p o r ; d e s i g n a t e d as gamma. / , exceeds 23i the l a t e n t heat of v a p o r i z a t i o n , L , by the q u a n t i t y * $ * A c c o r d i n g t o the theory ( l ) I = 1 - (3 @ m L u <= Tu &P u 1 - u dT I I I . P r e p a r a t i o n of. Samples, A l l o f the hydrocarbons used i n the present I n v e s t i g a t i o n were f u r n i s h e d by F . D, R o s s i n i i n c o n n e c t i o n w i t h the American Petro leum I n s t i t u t e Research P r o j e c t s 44 and 6^ » 8 » 9 , 1 0 , 1 1 ) a t the N a t i o n a l Bureau of S t a n d a r d s , I n c o n n e c t i o n w i t h the o amounts o f i m p u r i t y (not i n c l u d i n g water) i n the samples, and t h e " e f f e c t of such i m p u r i t i e s on the heat of v a p o r i z a t i o n * the f o l l o w i n g p o i n t s may be n o t e d : The manner of p r e p a r a t i o n and p u r i f i c a t i o n of the compounds was such as to l e a v e as i m p u r i t y o n l y those substances h a v i n g b o i l i n g p o i n t s and o ther p r o p e r -t i e s near those of the g i v e n substance . The amount o f such i m p u r i t y was l e s s than 0.01 mole f r a c t i o n f o r most of the compounds, between 0.01 and 0.02 mole f r a c t i o n f o r some* and near 0.03 mole f r a c t i o n f o r s e v e r a l . Examinat ion of the d i f -fe rences i n the v a l u e s o f the heat of v a p o r i z a t i o n f o r those c l o s e - b o i l i n g isomers t h a t might be expected t o be present i n one another as i m p u r i t i e s i n d i c a t e s t h a t i t i s h i g h l y improb-ab le t h a t any of the v a l u e s o f the heat o f v a p o r i z a t i o n w i l l be i n e r r o r by more than 1 i n 1000 because o f such i m p u r i t i e s . F o r most of the compounds* i t appears t h a t the e r r o r from these i m p u r i t i e s w i l l not exoeed 1 i n 2000 and f o r some the e r r o r 24. from t h i s source w i l l not exceed 1 I n 10 ,000 . I t was necessary to remove b o t h a i r and a t r a c e of water from the hydrocarbons b e f o r e making o a l o r i m e t r i c measurements on them. The a i r was e f f e c t i v e l y removed by d i s t i l l a t i o n i n t o a c o l d t r a p from whioh the a i r was c o n t i n u a l l y removed by pumping; The t r a p was immersed i n a s o l i d carbon d i o x i d e -e t h a n o l b a t h so t h a t there was n e g l i g i b l e l o s s of the sample. A second d i s t i l l a t i o n f rom the t r a p t o the detachable c o n t a i n e r i n d i c a t e d a l l the a i r had been removed. The water was u s u a l l y removed from the hydrocarbons by s l o w l y r u n n i n g the l i q u i d hydrocarbons through a tube packed w i t h s i l i c a g e l ; and i n t o the evacuated c o n t a i n e r from w h i c h the f i r s t d i s t i l l a t i o n was made. T e t r a e t h y l e n e c i t r a t e was used as a stopcock l u b r i c a n t w h i c h was not a f f e c t e d by the hydrocarbon . S i n c e t r a c e s of water were v i s i b l e as i c e i n the c o l d hydrocarbon even a f t e r t h i s d r y i n g p r o c e d u r e ; the e f f e c t i v e n e s s of the d r y i n g was measured; The sample of to luene was chosen f o r t h i s t e s t s ince i t seemed.to have more i c e v i s i b l e than most o f the hydrocarbons . The t o l u e n e sample was prepared I n the u s u a l manner and used i n the c a l o r i m e t e r i n the v a p o r i z a -t i o n exper iments ; Upon c o m p l e t i o n of these exper iments , the to luene was d i s t i l l e d to a bulb where the water content was measured by a method s i m i l a r to t h a t used by A l d r i c h (12) i n the d e t e r m i n a t i o n of water i n g a s o l i n e s . A l i q u i d a l l o y of •. sodium-potassium was added to the hydrocarbon and a g i t a t e d u n t i l a l l o f the water had r e a c t e d ; The p r e s s u r e of the 25. r hydrogen e v o l v e d was measured a f t e r the hydrooarbon had been f r o z e n w i t h l i q u i d a i r ; Prom t h i s p r e s s u r e ; and the volume and temperature o f the system, the water content was c a l c u l a t e d t o be l e s s than one p a r t i n 25,000 i n the sample. T h i s would a f f e c t the measured heat of v a p o r i z a t i o n of the toluene by l e s s t h a n 1 p a r t i n 5,000,* I t i s b e l i e v e d t h a t e r r o r due to water present was no more than t h i s amount i n any o f the h y d r o -carbons , and was u s u a l l y much l e s s , . F u r t h e r experiments were performed to o b t a i n a d d i t i o n a l evidence on the adequacy of the d r y i n g . I n a d d i t i o n to the d r y i n g w i t h - s i l i c a g e l , some experiments were made w i t h f r e e z -i n g out the water a t s o l i d carbon d i o x i d e temperatures and ii -f i l t e r i n g out the t r a c e of i c e w i t h f i b e r g l a s s ; Other e x p e r i -ments were made w i t h d r y i n g w i t h P2°5* A 1 1 these experiments i n d i c a t e d t h a t the d r y i n g of the hydrocarbons w i t h s i l i c a g e l was s u f f i c i e n t l y e f f e c t i v e . 17 ; E x p e r i m e n t a l procedure. ; 1 . A c c o u n t i n g f o r mass, energy, and change i n s t a t e of the sample; The mass of f l u i d withdrawn as vapor e n t e r s as a d i r e c t f a c t o r i n the r e d u c t i o n of the d a t a , and t h e r e f o r e the r e s u l t s can bB no more r e l i a b l e than the d e t e r m i n a t i o n s of these masses. S p e c i a l care was t h e r e f o r e taken to a v o i d e r r o r ; e i t h e r s y s -temat ic or a c c i d e n t a l i n the w e i g h i n g s ; An account was k e p t of the amount i n the c a l o r i m e t e r a t any time and a mass check made by comple te ly exhaus t ing and w e i g h i n g each charge a f t e r 26.. • a s e r i e s of exper iments ; The amount o f f l u i d evaporated and c o l l e c t e d by conden-s a t i o n was u s u a l l y not l e s s than 10 grams i n a s i n g l e e x p e r i -ment, a l t h o u g h i n a number o f cases where o n l y a s m a l l sample was a v a i l a b l e , s m a l l e r p o r t i o n s were t a k e n . To make the weighings w i t h s u i t a b l e p r e c i s i o n , the g l a s s c o n t a i n e r s h o l d i n g the condensed samples were g i v e n a p r e l i m -i n a r y r o u t i n e c o n d i t i o n i n g t r e a t m e n t . The c o n t a i n e r , h o l d i n g a sampleV which had been c o l l e c t e d by condensat ion i n a OOg' c o o l e r u s i n g dry i o e and a l c o h o l , was warmed to b r i n g i t t o the temperature of the room. The c o n t a i n e r was t h e n wiped dry and p l a c e d f i r s t i n f r o n t Of a f a n and then I n the ba lance case where i t was l e f t f o r at l e a s t 30 minutes to assume a s teady temperature . Weighings were then made by s u b s t i t u t i o n , e s t i -mat ing to 0 .1 mg by r e a d i n g swings . A dummy g l a s s c o n t a i n e r was ektp i n the balance case and was weighed e i t h e r j u s t b e f o r e or a f t e r the sample, t o e l i m i n a t e e r r o r s of w e i g h i n g due to a c c i d e n t a l changes i n balance or c o u n t e r p o i s e . The w e i g h t s were c o r r e c t e d f o r buoyancy i n a i r . Measured energy was s u p p l i e d e l e c t r i c a l l y t o the c a l o r i -meter and contents by means of the h e a t i n g c o i l i n s t a l l e d on the c a l o r i m e t e r s h e l l as d e s c r i b e d i n P a r t I ; Power was s u p p l i e d by a separate s torage b a t t e r y of l a r g e c u r r e n t capa-c i t y . Po tent iometer r e a d i n g s were made p e r i o d i c a l l y f o r ob-t a i n i n g the energy added e l e c t r i c a l l y , as d e s c r i b e d l a t e r ; I n order t o a v o i d a l a r g e i n i t i a l change when the c u r r e n t was swi tched t o the c a l o r i m e t e r h e a t e r a t the s t a r t o f an 27. exper iment , a s u b s t i t u t e r e s i s t o r was used t o a d j u s t and steady the b a t t e r y o u t p u t . Between experiments the c u r r e n t was a d j u s -t e d to a s e l e c t e d v a l u e to g i v e the d e s i r e d e v a p o r a t i o n r a t e . 5 The means p r o v i d e d f o r the c o n t r o l and e v a l u a t i o n of heat leak: have been d e s c r i b e d i n P a r t I , I n o p e r a t i o n , t h e r e were u s u a l l y s m a l l d e v i a t i o n s from the i d e a l c o n t r o l w h i c h would have a n n u l l e d heat l e a k . The s m a l l c o r r e c t i o n s f o r t h i s remain-i n g heat l e a k were eva luated w i t h the a i d of the d i f f e r e n t i a l thermoelements . The i n d i c a t e d d i f f e r e n c e s were observed every minute and added a l g e b r a i c a l l y t o g i v e sums i n temperature-time u n i t s c a l l e d " h e a t - l e a k c o e f f i c i e n t s " , gave the h e a t - l e a k c o r r e c t i o n s f o r the energy i n the i n d i v i d u a l experiments* The c a l o r i m e t e r was des igned to make the c o e f f i c i e n t s m a l l by con-s t r u c t i o n and by e v a c u a t i o n o f the i n s u l a t i n g space, and the m a n i p u l a t i o n of the envelope c o n t r o l was such as t o make the f a c t o r s m a l l . The c o r r e c t i o n - f o r heat l e a k u s u a l l y c o n s i s t e d of t h r e e p a r t s , des ignated as ' 'envelope 1 *, "tube?' , and " r e s i d u a l ' ' heat leaks> The envelope heat l e a k was u s u a l l y s m a l l on account of adjustment of the automatic c o n t r o l . The tube heat l e a k was p u r p o s e l y a l l o w e d to be l a r g e r by l e t t i n g the t h r o t t l e and" upper p a r t of the vapor tube r u n enough h i g h e r i n tempera-t u r e than the o a l o r i m e t e r s h e l l to a v o i d condensat ion i n the o u t f l o w tube* The heat l e a k c o e f f i c i e n t s were determined e x p e r i m e n t a l l y d u r i n g the e a r l y p a r t of the program and were checked l a t e r * T h i s was done by separate b lank experiments w i t h exaggerated 28; heat l e a k f a c t o r s , The energy changed, computed, f rom i n i t i a l and. f i n a l c a l o r i m e t e r temperatures and. heat c a p a c i t y was r e -duced, to energy p e r u n i t h e a t - l e a k f a c t o r . The r e s i d u a l h e a t - l e a k was t h a t w h i c h was not accounted f o r by the r o u t i n e envelope and tube h e a t - l e a k d e t e r m i n a t i o n s , because of p o s s i b l e d e v i a t i o n s of the h e a t - l e a k c o e f f i c i e n t s from the v a l u e s measured. T h i s r e s i d u a l h e a t - l e a k was accounted f o r by making f requent b l a n k experiments w h i l e the c a l o r i m e t e r was i n e q u i l i b r i u m between e v a p o r a t i o n e x p e r i m e n t s . I n t h e s e , bo th envelope and tube h e a t - l e a k s were kept normal and accounted f o r * l e a v i n g the d e v i a t i o n of the energy a c c o u n t i n g to g i v e a r a t e of l e a k p e r u n i t of t i m e , which i f of s i g n i f i c a n t amount, c o u l d be a p p l i e d to the p r e c e d i n g experiment as a s u p e r - c o r r e c t i o n . The temperature of the c a l o r i m e t e r and c o n t e n t s , when i n e q u i l i b r i u m ; was measured by r e s i s t a n c e thermometer i n con-j u n c t i o n w i t h thermoelements, as p r e v i o u s l y d e s c r i b e d ; The temperature change of the c a l o r i m e t e r and contents was thus always a c c u r a t e l y observed i n a l l exper iments ; A l l tempera-t u r e s were f i n a l l y expressed on the I n t e r n a t i o n a l Temperature S c a l e ; F o r de termin ing e i t h e r the i n i t i a l o r f i n a l temperature , each temperature o b s e r v a t i o n c o n s i s t e d o f s imultaneous r e a d i n g s of r e s i s t a n c e thermometer and thermoelements. The f i v e thermo-elements , 1 - 5, i n s e r i e s , i n d i c a t e d the mean temperature o f the c a l o r i m e t e r w i t h r e s p e c t to the r e f e r e n c e b l o c k . Four s u c c e s s i v e temperature r e a d i n g s were made a t l/2 minute i n t e r v a l s , from which the mean temperature was computed; 29. The temperature at which e v a p o r a t i o n proce'eded i s of some importance s inoe the heat v a p o r i z a t i o n v a r i e s w i t h temperature ; T h i s was c o n t r o l l e d by the o p e r a t o r t o keep i t as near as pos -s i b l e to the i n i t i a l t emperature . Thermoelement 5 was taken as the guide f o r t h i s c o n t r o l * s i n c e p r e v i o u s exper ience (4) and surveys of the temperature d i s t r i b u t i o n on the c a l o r i m e t e r s h e l l d u r i n g e v a p o r a t i o n . i n d i c a t e d t h a t t h i s p o i n t p r o b a b l y r e p r e s e n t e d the bes t a p p r o x i m a t i o n to the temperature of the vapor as i t l e f t the c a l o r i m e t e r . 2 ; D e s c r i p t i o n of v a p o r i z a t i o n experiments I n p r e p a r a t i o n f o r a s e r i e s of experiments on a sample, the sample; prepared as p r e v i o u s l y d e s c r i b e d was t r a n s f e r r e d t o the c a l o r i m e t e r by d i s t i l l a t i o n from the g l a s s c o n t a i n e r ; To do t h i s the c a l o r i m e t e r was surrounded by i c e w h i l e the necessary heat was s u p p l i e d to the c o n t a i n e r t o evaporate the l i q u i d . F o r some of the samples of h i g h e r b o i l i n g p o i n t was p r e s s u r e d i f f e r e n t i a l thus a v a i l a b l e r e q u i r e d . a l o n g t ime f o r the t r a n s f e r . The c a l o r i m e t e r and vapor l i n e were o f course c l e a r e d of a i r by e v a c u a t i o n b e f o r e c h a r g i n g . A f t e r the sample was i n * the c o n t a i n e r was re -weighed and the c a l o r i m e t e r was. heated to the temperature o f measurement; u s u a l l y 25 °C; k e e p i n g the v a l v e and tube above the c a l o r i m e t e r temperature to a v o i d condensat ion i n the t u b e ; I f n e c e s s a r y ; the tube was d r i e d by a f t e r - h e a t i n g . I n t h i s p r e l i m i n a r y c h a r g i n g the i n s u l a t i n g space was f i l l e d w i t h h e l i u m t o promote heat f l o w o u t . Before s t a r t i n g the experiment t h i s spaoe was evacuated to improve 30. the i n s u l a t i o n . A weighed g l a s s c o n t a i n e r was a t t a c h e d and the l i n e evacu-a ted to the t h r o t t l e v a l v e ; The c o n t a i n e r was opened to the l i n e and the apparatus was then ready t o s t a r t the exper iment ; The i n i t i a l e q u i l i b r i u m temperature o f the c a l o r i m e t e r and contents was observed ; A t the zero of a chosen minute the c u r r e n t was switched from the s u b s t i t u t e r e s i s t o r to t h e c a l o r -i m e t e r h e a t e r by the automatic t i m e - t r i p p e d s w i t c h . The t h r o t t l e v a l v e was opened by the operator .who was a l s o o b s e r v i n g the thermoelements; The v a l v e was a d j u s t e d t o keep 3 a t zero# The r e f e r e n c e b l o c k was kept a t a constant temperature as shown by the r e s i s t a n c e thermometer; The upper p a r t o f t h e o a l o r ? i m e t e r which c l o s e l y f o l l o w e d the e v a p o r a t i o n temperature was m a i n t a i n e d at the i n i t i a l r e f e r e n c e b l o c k temperature by r e g u -l a t i n g the vapor f l o w through the v a l v e t o j u s t ba lance the energy added to the c a l o r i m e t e r ; D u r i n g the e v a p o r a t i o n p e r i o d the l o w e r p a r t of the c a l o r i m e t e r i n contac t w i t h the l i q u i d became warmer by the amount of superhea t ing necessary to conduct the heat to the sur face f o r e v a p o r a t i o n . To eva luate the h e a t - l e a k f a c t o r s , . t h e d i f f e r e n t i a l thermo-elements; 1 9 - 10, and 7 - 5, were observed at 1 minute i n t e r v a l s ; The constancy of the r e f e r e n c e - b l o c k temperature was f r e q u e n t l y checked to f u r n i s h a steady zero f o r thermos element j?, used to guide the r e g u l a t i o n of the e v a p o r a t i o n temperature . ^Occas ional surveys of a l l thermoelements were made to i n d i c a t e any f o r t u i t o u s i r r e g u l a r i t i e s i n b e h a v i o r ; The c u r r e n t and p o t e n t i a l drop i n the c a l o r i m e t e r h e a t e r were 3 1 . observed on a l t e r n a t e minutes , s t a r t i n g l/2 minute a f t e r the power was swi tched o n . A t the end of the chosen number of minutes , the c u r r e n t was swi tched back from the c a l o r i m e t e r h e a t e r to the c a l o r -imeter h e a t e r t o the s u b s t i t u t e r e s i s t o r , making the t ime f a c t o r of the energy an i n t e g r a l number of minutes as determined by the s tandard c l o c k . The t h r o t t l e v a l v e was kept open l o n g enough to b r i n g the c a l o r i m e t e r and contents to f i n a l e q u i l i -br ium temperature near the i n i t i a l t emperature , u s u a l l y w i t h i n 0 . 0 1 ° C . A f t e r a pause of 10 minutes f o r a t t a i n i n g e q u i l i b r i u m , the f i n a l temperature was o b s e r v e d . F o l l o w i n g t h a t o b s e r v a t i o n , and w h i l e changing c o n t a i n e r and w e i g h i n g a p r e v i o u s sample, a b l a n k experiment was conducted to o b t a i n the r e s i d u a l hea t -l e a k f a c t o r , p r e v i o u s l y d e s c r i b e d ; On most of the samples; experiments were made at s e v e r a l r a t e s o f e v a p o r a t i o n , u s u a l l y between l / 4 and 1 gram per m i n u t e ; Other r a t e s s m a l l e r t h a n 1/4 gram/min were a l s o used e i t h e r because o f l i m i t a t i o n s on aooount of the f l u i d c h a r a c -t e r i s t i c s , or e l s e because of the l i m i t e d amount o f sample,; The p r a c t i c e of u s i n g d i f f e r e n t r a t e s of e v a p o r a t i o n was to f u r n i s h a check on s e v e r a l c o n c e i v a b l e sources of e r r o r ; T h i s p r a c t i c e has been f o l l o w e d f o r the pas t 30 years as a check on the v a r i o u s p r e v e n t i v e measures f o r a v o i d i n g l i q u i d mixed w i t h the vapor i n e v a p o r a t i o n exper iments . A l t h o u g h I n the pas t these measures were so e f f e c t i v e t h a t no case was ever found where t h i s change of r a t e gave a p o s i t i v e t e s t f o r wet steam, even over the range from the i c e p o i n t to w i t h i n 32. one degree of the c r i t i c a l temperature , the t e s t has been cont inued as a r o u t i n e safeguard a g a i n s t erroneous e v a l u a t i o n of the s t a t e o f the v a p o r . I n the present case , i f spray p r o j e c t e d upward from the e v a p o r a t i n g sur face escaped capture by the b a f f l e s and was withdrawn i n the v a p o r , the measured energy p e r u n i t mass would be too s m a l l . Or* i f the temperature of the vapor i n d i -ca ted by the o b s e r v a t i o n of 5 thermoelement was i n e r r o r ; the e f f e c t of the e r r o r might depend on the r a t e o f f l o w . Absence of such evidence of any e f f e c t of the r a t e on the r e -s u l t i n g v a l u e of the heat of v a p o r i z a t i o n , may be taken as c o n t r i b u t i n g to the r e l i a b i l i t y of the r e s u l t s as f a r as the s t a t e of the f l u i d i s concerned. Here a g a i n , i t must be con-f e s s e d the t e s t showed no evidence of l i q u i d mixed w i t h the v a p o r . The b a f f l e s e v i d e n t l y have done t h e i r b i t . F u r t h e r evidence of r e l i a b i l i t y ; as d i s t i n g u i s h e d from c o n s i s t e n c y ; was f u r n i s h e d by the experiments on w a t e r . V . RESULTS OF VAPORIZATION EXPERIMENTS. The r e s u l t s of the v a p o r i z a t i o n experiments are g i v e n i n c h r o n o l o g i c a l o rder i n Table I . The v a l u e s of Net Energy g i v e n i n column 6 i n c l u d e not o n l y the e l e c t r i c a l energy i n p u t , but a l s o the energ ies due to the v a r i o u s heat l e a k s (envelope , tube , and r e s i d u a l ) , the c o r r e c t i o n f o r the change i n tempera-t u r e of the c a l o r i m e t e r between the b e g i n n i n g and the end of the experiment , and the c o r r e c t i o n f o r any d e v i a t i o n of the 3 3 . e v a p o r a t i o n temperature from the d e s i r e d even temperature ( u s u a l l y 2 5 ° C ) . These components o f the net energy are not l i s t e d s e p a r a t e l y because the c o r r e c t i o n s are so s m a l l . I n an average experiment , the a r i t h m e t i c a l sum of the heat l e a k c o r r e c t i o n s o n l y amounts to about one j o u l e , w h i l e the o ther c o r r e c t i o n s are even l e s s . T h i s i s the r e s u l t of c a r e f u l i c o n t r o l of the temperature of the c a l o r i m e t e r and i t s s u r -roundings at a l l t imes d u r i n g an exper iment . The Value of Gamma, t» g i v e n i n column 7* i s o b t a i n e d by d i v i s i o n of the v a l u e o f Net Energy ( c o l . 6) by the mass ( c o l . 4 ) . T h i s q u a n t i t y ; Gamma, )( , i s g r e a t e r t h a n the l a t e n t heat of v a p o r i z a t i o n by the q u a n t i t y B e t a , ft as des -c r i b e d p r e v i o u s l y ( l ) i n the method. I n o t h e r words ; L « % - <5 The q u a n t i t y 3 » w h i c h i s v e r y s m a l l i n most of the exper iments , i s c a l c u l a t e d the r e l a t i o n (3 s T u dP I T where T i s a b s o l u t e temperature , u i s s p e c i f i c volume of the l i q u i d ; and dP/dT i s the vapor p r e s s u r e s l o p e . V a l u e s o f vapor p r e s s u r e s lope and l i q u i d s p e c i f i c volume were c a l c u -l a t e d from d a t a g i v e n i n v a r i o u s sources (13» 1 4 ) . S i n c e the q u a n t i t y /3 i s s m a l l ; h i g h accuracy was not r e q u i r e d i n the source d a t a . C a l c u l a t e d v a l u e s of X a r e l i s t e d i n column 9 w h i l e the d e r i v e d v a l u e s of heat of v a p o r i z a t i o n ar,e l i s t e d i n column 1 0 . I n s p e c t i o n of Table I shows some d u p l i c a t i o n of e x p e r i -ments w i t h a few m a t e r i a l s . T h i s was due to e i t h e r an 34 . i n v e s t i g a t i o n o f the e f f e c t of v a r i o u s d r y i n g methods, o r t o the a v a i l a b i l i t y of a p u r e r sample a t a l a t e r d a t e ; E t h y l benzene and 2 , 3 ^ d i m e t h y l pentane are examples Of the l a t t e r and v a l u e s o f heats of v a p o r i z a t i o n on b o t h samples o f d i f f e r -ent p u r i t y are g i v e n to show the s m a l l e f f e c t on the r e s u l t ; The d i f f e r e n c e s are l e s s t h a n 0.1%. The hydrocarbons 2 , 2^ d i m e t h y l butane and t r a n s 1 , 4 - d i m e t h y l cyclohexane were chosen t o i n v e s t i g a t e the d i f f e r e n t d r y i n g methods. The r e s u l t s u s i n g d i f f e r e n t d r y i n g methods agreed to b e t t e r than O.Olfo. Measurements on the heat of v a p o r i z a t i o n of water were made"before, d u r i n g * a n d : a f t e r the s e r i e s o f hydrocarbon exper iments . T h i s procedure served as an a d d i t i o n a l check on the apcuraoy of the, r e s u l t s * The average of the 15 water experiments gave a v a l u e of heat of v a p o r i z a t i o n a t 25°C of 2441.37 i n t . j / g as opmpared to 2441.40 o b t a i n e d w i t h an e a r l i e r c a l o r i m e t e r ( 4 ) ; The average d e v i a t i o n f rom t h i s e a r l i e r v a l u e was 0.015%. V I . ACCURACY OF RESULTS Off HEAT OF VAPORIZATION. I n v iew of the p u r i t y o f the hydrocarbons ; smal lness of heat l e a k s , and the e x c e l l e n t agreement o f the r e s u l t i n g heats of v a p o r i z a t i o n of water, w i t h those w i t h a d i f f e r e n t c a l o r -i m e t e r , i t i s b e l i e v e d t h a t the probable e r r o r i n the heats Of v a p o r i z a t i o n of the hydrocarbons l i s t e d i n Table I i s about 0;1%. I n the case of hexamethyl ethane* e x p e r i m e n t a l d i f f i c u l t i e s due to the f a c t t h a t the m a t e r i a l was a s o l i d a t 25°C l e a d to an es t imated probable e r r o r of about 2% i n 35. the observed heat of s u b l i m a t i o n . I t has a l s o been shown (1) t h a t the q u a n t i t y oC i s r e l a t e d to the w e l l known e n t h a l p y , H , by the r e l a t i o n H «= & + Q where ft = L u = Tu dP u ' - u d"? where u 1 and u are the s p e c i f i c volumes of the s a t u r a t e d vapor and l i q u i d , r e s p e c t i v e l y , L the heat of v a p o r i z a t i o n , T the a b s o l u t e temperature , and dP/dT the vapor p r e s s u r e s l o p e . At the temperatures of the present exper iments , the t e r m ( 3 i s q u i t e s m a l l compared to oC so t h a t the v a l u e of cC i s w i t h i n a few p a r t s i n a thousand o f the va lue o f H . The v a l u e o f All/ A T f o r a g i v e n temperature i n t e r v a l i s A H = AoC_ + A3 $ T /|T A T and the v a l u e of dH/dT a l o n g the s a t u r a t i o n p a t h i s d e r i v e d by a p p l y i n g a c o r r e c t i o n f o r c u r v a t u r e of the entha lpy f u n c t i o n . The c a l c u l a t i o n o f C s a t » the heat c a p a c i t y of the l i q u i d a l o n g the s a t u r a t i o n p a r t , f rom t h e v a l u e s of ( d H / d T ) s a j ; i s performed by u s i n g the fundamental d e f i n i t i o n s of H and G s a-(j. dH = d E + P d u + u d P cCfgat d"f 17 d"!F c s a t " <3LQ, » dE + P du o T s a t d"T . TCP ' Hence*1 c s a t " S ' u 5£ ^ s a t ^ - dH - /3 ^ s a t " T " 36. In the temperature and pressure range of these experiments, the values of C s a t are very olose to the values of Cp.=i atm.» probably within 0 .2%. If desired, the value of G p may be oal-> culated'from the relation C p - 1 - C s a t + _ 6 _ + T . d 2u (P-l) - dP dH T dT* dT dP where P i s expressed in atmospheres. Accurate knowledge of specific volume i s necessary i n order to evaluate the factor d2u . III. EXPERIMENT:AL PROCEDURE. The experimental procedure in the heat capacity experi-; ments i s very similar to that with the vaporization experiments; With a high f i l l i n g i n the calorimeter, the calorimeter was brought to equilibrium at the desired starting temperature and i t s temperature observed as noted in Parts I and II. Measured electrical power was put into the calorimeter heater to heat the calorimeter at a rate of very olose to l / 2 deg per min. r At the same time, the power input to the envelope heater, the throttle heater, and the reference block heater were carefully regulated; The reference block heater current was regulated manually so that the reference block temperature was always very close to the calorimeter temperature; The envelope heater regulation was by two means. The heater was composed of two entirely separate parts. One part 37. was d i s t r i b u t e d a p p r o x i m a t e l y a c c o r d i n g to area so t h a t when the envelope was at a s teady temperature , the temperature g r a d i e n t due to heat i n p u t i n t h i s h e a t e r would be a minimum. The o ther p a r t was d i s t r i b u t e d on the envelope a p p r o x i m a t e l y a c c o r d i n g t o heat c a p a c i t y so t h a t w h i l e the envelope , a m i n i -mum g r a d i e n t would o c c u r ; A c t u a l l y i n the heat c a p a c i t y e x p e r i -ments* b o t h p a r t s o f the h e a t e r were u s e d . The f i r s t p a r t was used a l l the t ime and was r e g u l a t e d a u t o m a t i c a l l y as d e s c r i b e d i n P a r t I . The second p a r t was used o n l y d u r i n g h e a t i n g p e r i o d s * when the envelope was heated at a r a t e of l/2 deg/min t o s t a y c l o s e t o the temperature of the c a l o r i m e t e r . The heat i n p u t to t h i s second p a r t of the envelope Was se t once and not changed, s i n c e the f i r s t p a r t of the hea ter accounted f o r s m a l l v a r i a -t i o n s i n the heat c a p a c i t y o f the envelope , as w e l l as f o r changes i n heat l o s t t o t h e o u t s i d e ; The t h r o t t l e h e a t e r was r e g u l a t e d a u t o m a t i c a l l y * as i n P a r t I , so t h a t the temperature o f the t h r o t t l e was h i g h enough t o prevent any p a r t of the tube from becoming c o l d e r than the temperature of the vapor i n the c a l o r i m e t e r . T h i s p r e c a u t i o n was necessary to a v o i d condensat ion i n the t u b e . A f t e r the c a l o r i m e t e r had heated the d e s i r e d amount - ( e i t h e r 5 or 10 degrees ) , the c a l o r i m e t e r power was t u r n e d o f f and the c a l o r i m e t e r a l l o w e d to come to e q u i l i b r i u m , as i n d i c a t e d by thermoelements l o c a t e d on the c a l o r i m e t e r ; Due t o the e f f e c t -i v e n e s s of the heat d i s t r i b u t i n g system i n the c a l o r i m e t e r , the time to come to e q u i l i b r i u m was o n l y a few m i n u t e s . U s u a l l y about 10 minutes was a l l o w e d w h i c h was c o n s i d e r a b l y l o n g e r 3 8 . than n e c e s s a r y , j u d g i n g from the thermoelement r e a d i n g s ; The temperature of the c a l o r i m e t e r was then observed as b e f o r e and a new h e a t i n g p e r i o d s t a r t e d . Measurements of heat l e a k co -e f f i c i e n t s (enve lope , t h r o t t l e , and r e s i d u a l ) were made as i n P a r t I I except t h a t the r e s i d u a l heat l e a k was checked o n l y at the b e g i n n i n g and end of a s e r i e s of heat c a p a c i t y measurements. I T . RESULTS OF HEAT CAPACITY EXPERIMENTS. The r e s u l t s o f the heat c a p a c i t y experiments are g i v e n i n Table I I . Column 3 g i v e s the mass of f l u i d i n the c a l o r i m e t e r i n the experiments f o r the data l i s t e d ; The c o r r e s p o n d i n g heat of v a p o r i z a t i o n experiments i n Table I were made a f t e r the h i g h - f i l l i n g experiments and b e f o r e the l o w - f i l l i n g exper iments . Column 4 i n d i c a t e s the type of heat f u n c t i o n f o r w h i c h c o r r e s -ponding v a l u e s are l i s t e d i n columns 5 t o 9 f o r the v a r i o u s temperature i n t e r v a l s covered by the exper iments ; F o r example, the l o w - f i l l i n g experiments w i t h n-heptane on Nov; 22, 1941 gave f o r the temperature i n t e r v a l 20 to 30°C a v a l u e of Q//1 T of 81.21 i n t ; j . / d e g ; The v a l u e s of §JA T thus l i s t e d i n Table I I are c a l c u l a t e d from the e l e c t r i c a l energy i n p u t d u r i n g the exper iment , c o r -r e c t e d f o r the t h r e e heat l e a k s d e s c r i b e d i n P a r t I I and f o r the departures of the b e g i n n i n g and end temperatures of the experiment from the d e s i r e d even temperature . As i n the v a p o r i z a t i o n exper iments , the a r i t h m e t i c a l sum of the heat 39. l e a k s f o r an average experiment was about one or two j o u l e s , most of whioh i s caused by r e g u l a t i n g the upper tube warm t o a v o i d condensa t ion ; The heat l e a k on most experiments a f f e c t e d the r e s u l t s by o n l y about 0.2% and even t h i s s m a l l amount was e f f e c t i v e l y e l i m i n a t e d by the exper imenta l procedure which gave the same heat l e a k c o n d i t i o n s i n the h i g h - f i l l i n g experiments as i n the l o w - f i l l i n g experiments, . The b e g i n n i n g and end temperatures of the c a l o r i m e t e r i n the heat c a p a c i t y experiments were u s u a l l y r e g u l a t e d t o w i t h i n a few hundredths of a degree of the d e s i r e d even temperatures so t h a t the r e s u l t a n t c o r r e c t i o n s a p p l i e d to the measured 0 /A T amounted to l e s s t h a n 1$. S ince the heat c a p a c i t y of the c a l o r i m e t e r and contents i s known from the experiments by the method of a p p r o x i m a t i o n , these c o r r e c t i o n s should i n t r o d u c e no a p p r e c i a b l e e r r o r i n the r e s u l t s . The v a l u e s of j & T l i s t e d i n Table* I I are o b t a i n e d by d i v i d i n g the d i f f e r e n c e between the average v a l u e s of Q/A T f o r the h i g h - f i l l i n g experiment and c o r r e s p o n d i n g average v a l u e s of Q / 4 T f o r the l o w - f i l l i n g exper iment , byZ\M, the d i f f e r e n c e i n the.masses of f l u i d i n the c a l o r i m e t e r i n the h i g h and l o w - f i l l i n g exper iments . Va lues of AE/AT are c a l c u -l a t e d from Act/ AT by adding A&IAT c a l c u l a t e d from s p e c i f i c volume and vapor p r e s s u r e d a t a as d e s c r i b e d under Method • Values of C s a 1 ; a t the mid temperatures of the i n t e r v a l s are c a l c u l a t e d from 4 H / / I T by f i r s t a p p l y i n g a c u r v a t u r e c o r r e c -t i o n to get dH/dT at the mid temperature of the i n t e r v a l s , and then s u b t r a c t i n g v a l u e s of (^/T ; A l l these c o r r e c t i o n s 40 . are s m a l l so t h a t the r e s u l t i n g v a l u e s of C s a t do not d i f f e r from the AoC / A T by more than a few p a r t s p e r thousand. I n order t o "smooth" the d a t a , an e q u a t i o n o f the form G s a t " A * B T f g t 2 w a s f i t t e d t o the 4 * t a f o r each m a t e r i a l by the method of l e a s t squares . Table I I I g i v e s the constants of the e q u a t i o n f o r the 12 hydrocarbons as w e l l as v a l u e s a t 5 -degree i n t e r v a l s i n the exper imenta l range as c a l c u l a t e d f rom these e q u a t i o n s . The v a l u e s o f C s a ^ ( c a l c ) l i s t e d i n Table I I are a l s o computed f rom these equat ions i n o r d e r to judge the a c c i d e n t a l v a r i a t i o n s i n the e x p e r i m e n t a l v a l u e s of heat c a p a c i t i e s . I t was found t h a t the average d e v i a t i o n of a deter-m i n a t i o n of heat c a p a c i t y f r o m , t h e v a l u e c a l c u l a t e d f rom the equat ions was 0.011% f o r the ten-degree i n t e r v a l s and 0.022% f o r the f i v e - d e g r e e i n t e r v a l s . S i m i l a r to the v a p o r i z a t i o n exper iments , heat c a p a c i t y experiments w i t h water were made at the b e g i n n i n g of t h i s s e r i e s o f measurements and near the end', as a check on the accuracy of the r e s u l t s . I t was found t h a t the 30 experiments w i t h water gave an average d e v i a t i o n of A<*/AT o f about 0.025% from the v a l u e s r e p o r t e d w i t h another c a l o r i m e t e r ( 4 ) . I n a d d i t i o n to the check on . the heat c a p a c i t y o f watery i t was p o s s i b l e to a l s o check on v a l u e s o f heat c a p a c i t y of n-heptane as determined i n the same l a r g e c a l o r i m e t e r 4 as used w i t h w a t e r . These u n p u b l i s h e d d e t e r m i n a t i o n s were made i n 1939 by Osborne, S t imson , and Ginnings w i t h a sample o f n - h e p -tane f u r n i s h e d by D . B . Brooks of t h i s B u r e a u . Three s e r i e s of l o w - f i l l i n g experiments were made over the temperature 4 1 . range 5-100*0, .but- o n l y one s e r i e s of h i g h - f i l l i n g experiments was completed, i n the range 5-9Q 9C on account of i n t e r r u p t i o n o f the experiments by a mechanica l breakdown, The r e s u l t s of the 1939 measurements on n-heptane are g i v e n i n Table I V , Columns 2 and 3 g i v e the Net Energy i n p u t s f o r the low-and h i g h - f i l l i n g exper iments , h a v i n g 85,859 and 743**123 grams .of heptane, r e s p e c t i v e l y . These v a l u e s of Net Energy i n c l u d e heat l e a k c o r r e c t i o n and c o r r e c t i o n s f o r end temperatures . The v a l u e s of Z J * / 4 T i n column 4 were o b t a i n e d by d i v i d i n g the d i f f e r e n c e i n Net E n e r g i e s f o r the h i g h and low f i l l i n g s by the product of the d i f f e r e n c e i n mass of heptane (657,264) t imes the number of degrees i n the temperature i n t e r v a l . The Va lues of # / T i n c o l , 8 and A&I & T i n c o l , .5 were c a l c u l a t e d from l i q u i d s p e c i f i c volume data i n the I n t e r n a t i o n a l C r i t i c a l Table (10) and vapor p r e s s u r e data from M a i r et a l (9) u s i n g the r e l a t i o n / 3 = Tu dP/dT. The v a l u e s of C s a t were c a l c u l a t e d from Aoc/A T by the method used i n Table I I , An e q u a t i o n of the type C s a t = A + BT + C T 2 was f i t t e d to the observed v a l u e s of C s a t l i s t e d i n Table I V , g i v i n g v a l u e s o f the cons tants as A » 2,15453» B • ,0033961, and C.= 6.7909 x 10"^ , when T i s i n deg , C and G s a t i s i n i n t » G « T n e average d e v i a t i o n of the 1939 observed v a l u e s f rom the v a l u e s c a l c u l a t e d from t h i s equat ion i s 0.028%, w h i l e the average d e v i a t i o n o f the 1941 observed v a l u e s from t h i s e q u a t i o n (based on the 1939 r e s u l t s ) i s 0.037%. A comparison of the observed v a l u e s i s g i v e n i n F i g , ] * , 42. V*. DISCUSSION OP ACCURACY OP HEAT CAPACITY RESULTS • A When the c a l o r i m e t e r was designed* i t was not expected t h a t i t would g i v e as accurate r e s u l t s i n the heat c a p a c i t y measurements as i n the v a p o r i z a t i o n exper iments . T h i s was due to the s m a l l s i z e o f the c a l o r i m e t e r w h i c h was a more important f a c t o r i n the heat c a p a c i t y experiments than i n the v a p o r i z a t i o n exper iments . However, i n v iew o f the e x c e l l e n t agreement o f the v a l u e s of heat c a p a c i t y of water and heptane w i t h v a l u e s obta ined w i t h a l a r g e c a l o r i m e t e r at an e a r l i e r d a t e , i t i s b e l i e v e d t h a t the c a l o r i m e t e r i s capable of b e t t e r t h a n O . l f . i n heat c a p a c i t i e s i n s p i t e o f i t s s m a l l s i z e . S i n c e some of the heat c a p a c i t y r e s u l t s are based on scanty d a t a , and some ( s u c h as n-deoane) i n v o l v e s m a l l e r amounts of hydrocarbon i n the c a l o r i m e t e r than o t h e r s , i t i s b e l i e v e d t h a t the probable e r r o r i n the heat c a p a c i t y r e s u l t s v a r i e s f rom 0.1% w i t h most h y d r o -carbons such as n-^heptane to 0.3% w i t h n-deoane . REFERENCES 1. Nathan S . Osborne* C a l o r i m e t r y of a f l u i d , B . S , J . Research 4, 609 (1930) 2. N . S . Osborne, H . F . S t imson , and E , F . F i o c k * A o a l o r i m e t r i o d e t e r m i n a t i o n of thermal p r o p e r t i e s o f s a t u r a t e d water and steam from ,0°C to 2?0°C, BS J . Research £» 411 (1930). 3 . N . S i Osborne, E . F* St imson and D . C . G i n n i n g a , C a l o r i m e t r y d e t e r m i n a t i o n of the thermodynamic p r o p e r t i e s of s a t u r a t e d water i n b o t h the l i q u i d and gaseous s t a t e s from 100 t o 374°C* J ; Research NBS l 8 » 389 (1937)• 4. Nathan S . Osborne, H a r o l d F . S t i m s o n , and Defoe C . G i n n i n g s , .Measurements of heat, c a p a c i t y and heat of v a p o r i z a t i o n of water i n the range 0 ° to 100°C, J . Research NBS 23, 197 (1939)• 3 . C y r i l H . Meyers , C o i l e d - f i l a m e n t r e s i s t a n c e thermometers, BS J i Research £» 807 (1932). 6; E . F . M u e l l e r , Wheatstone b r i d g e s and some accessory apparatus f o r r e s i s t a n c e thermometry. B u l l . BS 13* 547 (1916) S 288 7 . E . J . R . Prosen and F . D . R o s s i n i Heats of i s o m e r i z a t i o n of the f i v e hexanes J . Res . NBS 22., 289 (1941). 8; E . J . R . Prosen and F . D . R o s s i n i Heats of i s o m e r i z a t i o n of the n i n e heptanes . J , Res . NBS 2J_; 319 (1941); 9; Bever idge J ; M a i r , Domenic J . T e r m i n i , C h a r l e s B . W i l l i n g h a m , and F r e d e r i c k D, R o s s i n i , ; P u r i f i c a t i o n and s e a l i n g t i n vacuum" o f N a t i o n a l Bureau o f Standard Samples of hydrocarbons . J ; Res . NBS jJT, 229 (1946). 10. 11 . References ( o o n t . ) 1 2 . E l i z a b e t h W. A l d r i c h S o l u b i l i t y of water i n a v i a t i o n g a s o l i n e s ; I n d . and E n g . Chem. j5> 348 ( 1 9 3 1 ; * 1 3 . Tables of p h y s i c a l cons tants of s e l e c t e d hydrocarbons i s s u e d by the American Petro leum I n s t i t u t e . 14 . I n t e r n a t i o n a l C r i t i c a l Tables j5 M c G r a w - H i l l Book C o ; ; I n c . ; Hew York C i t y ; (1928) . Ice Serf? /?efene/?ceJ<s/7c7?o/? for 7fcjf/ ^/d POTENTlOfllET&R FOR. CUP STEM HEAT LEAK CONTROL. r/Kp/. s vs. Thcpi 6 BATH CURRS/VT CONTROL Current* m 77icp/ /S~ SHfELD H£ATLLzAKCONTROL (Zi-8) VS. <r[Or//J lempcrarj 7 V$ tO There art extra heater arret Hzermocaapfc Jeacts -faten to boflfr /V?e t~e/7r/7er//?y f?//7j & the tjefen?/?ce 6/oc/f are frcct off ffervi for ft/fane e/se 'f Copper Lead Wires. — Constantan Side cf Thermocouple Copper- S,cte of Thermocouple. userf0/7/g farzerv bo/a/?ce WIR/NQ D/AGRAM FDR CALOR/M£r£R Drawn Bt{ . Date • AugG/W. 1—1—I I — 1 I I I I I I 0 5 10cm 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0059098/manifest

Comment

Related Items