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The extraction of tin from its ores and the preparation and behavior of certain pure salts of tin Marshall, Harry Borden 1931

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THE EXTRACTION OF TIN FROM ITS ORES AND THE PREPARATION AND BEHAVIOR OF CERTAIN P M E SALTS OF TIN.  by  Harry Borden M a r s h a l l  A Thesis submitted f o r the Degree o f MASTER OF ARTS i n the Department  CHEMISTRY  The U n i v e r s i t y of B r i t i s h Columbia A p r i l - 1931.  TABLE OF CONTENTS  INTRODUCTION. I.  EXTRACTION OF TIN FROM ITS ORES. 1.  Occurrence of Samples.  2.  D i s i n t e g r a t i o n of G a s s i t e r i t e .  3.  D i s i n t e g r a t i o n of Stannite.  4.  P u r i f i c a t i o n of C a s s i t e r i t e T i n .  5. P u r i f i c a t i o n o f Stannite T i n .  II.  THE STABILITY OF STANNIC OXIDE.  I I I . THE DETERMINATION OF TIN AS CAESIUM CHLOROSTANNATE. 1.  P r e p a r a t i o n of Stannic C h l o r i d e .  2. P r e p a r a t i o n o f Caesiian 0hloride. r  3. IV.  Method.  SOLUBILITY OF CAESIUM CHLOROSTANNATE.  ACKNOWLEDGMENT  I wish to express my greatest appreciation and thanks to Dr. E.H. Archibald, who has not only provided many materials necessary i n t h i s i n v e s t i g a t i o n but has also gladly given every possible assistance and advice.  THE EXTRACTION OF TIN FROM ITS ORES AND THE PREPARATION AND BEHAVIOR OF CERTAIN PURE SALTS OF TIN.  INTRODUCTION. The existence of isotopes has explained a great manyd i s c r e p a n c i e s i n the theory of atomic s t r u c t u r e .  I t has also  d e f i n i t e l y s e t t l e d the v a l i d i t y o f the whole number r u l e f o r the atomic weights of the elements.  Henee any experimental  work whieh w i l l corroborate the existence o f i s o t o p e s , w i l l be o f great importance i n strengthening the proof of the atomic Theory. 1 F. W. Aston, by u s i n g the p o s i t i v e ray spectograph, and p l a t e s of i n c r e a s e d s e n s i t i v i t y to p o s i t i v e rays, has found i t p o s s i b l e t o d e f i n i t e l y prove that a group of eight l i n e s , corresponding approximately t o atomic weights of 116, 117, 118, 119, 120, 121, 122, 124, was due t o T i n .  I t i s extremely  l i k e l y that these eight i s o t o p e s do e x i s t i n the case of t i n , but as y e t no d i r e c t chemical evidence has proven t h e i r existence. One method of a t t a c k i n g t h i s problem i s t o determine the atomic weight of t i n i n i t s d i f f e r e n t ores.  Due to extremely  d i f f e r e n t g e o l o g i c a l formation there may be wide v a r i a t i o n s i n the concentration of the isotopes i n these d i f f e r e n t ores. Such a v a r i a t i o n might be detected by separate atomic weight determinations of the t i n i n the d i f f e r e n t samples.  T h i s was the o r i g i n a l problem attempted.  However, the  e x t r a c t i o n of t i n from i t s ores proved to c o n s t i t u t e a problem i n i t s e l f , and t h i s t h e s i s w i l l deal l a r g e l y w i t h t h i s p a r t of the work, together w i t h the preparation of pure t i n from the m a t e r i a l e x t r a c t e d . Considerable work has been c a r r i e d out towards evolving a convenient and g e n e r a l l y a p p l i c a b l e method of a n a l y s i n g t i n ores.  This search has brought f o r t h many methods of  d i s i n t e g r a t i o n and may be b r i e f l y reviewed under two headings: A. Reduction methods i n which the oxide i s reduced to m e t a l l i c t i n . B. S a l i f i c a t i o n methods i n whieh advantage i s taken o f the a c i d p r o p e r t i e s of stannie oxide i n the formation of a l k a l i  stannates.  A. Reduction Methods: C o r n o u a i l l e s f i r s t used carbon as a reducing agent f o r 2 t i n ores. The process has been studied by l e v o l and Moissenet, 4 but i t i s best described by B e r i n g e r . He a l s o suggests the a d d i t i o n of a l i t t l e powdered f l u o r spar to a s s i s t the f u s i o n of r e f r a c t o r y s l a g s . The method of r e d u c t i o n i n hydrogen or i l l u m i n a t i n g gas 5 i s due to Hampe, but has been described i n some d e t a i l by 6 ,7 Parry.  Fawns considers i t the most p r a c t i c a l method of  reduction. Reduction w i t h potassium cyanide has been used by 6 8 a s s a y i s t s f o r some time. P a r r y and Bayerlein-Essen have o u t l i n e d t h e i r methods of a n a l y s i n g t i n ore w i t h t h i s reagent.  3 9  a. M. Henderson has found that t h i s method of f u s i o n i s out 10 of the question f o r low grade ores.  0. Boy  ascribes this  i n e f f i c i e n c y f o r low grade ores to the presence of sulphur or s i l i e a , and m o d i f i e s the procedure by f i r s t r o a s t i n g to remove sulphur, and then b o i l i n g w i t h h y d r o f l u o r i c a c i d to remove s i l i e a . B. S a l i f i c a t i o n Methods: F u s i o n w i t h sodium carbonate and sulphur to form soluble 11 12 sulpho-stannates, has been worked out by G o l i c k and C o r t i . 13 J. Gray  has found t h i s to be an accurate method, but describes  i t as " d i r t y , tedious, and slow."  This conclusion has been  a f f i r m e d by S. Fawns who also adds that f o r t h i s reason the method i s never used. 14 E. ?. Pearce  suggested the use of sodium hydroxide f o r  the d i s i n t e g r a t i o n of t i n ores and worked out a scheme of a n a l y s i s based on t h i s method of f u s i o n . The present accepted method i s a s l i g h t m o d i f i c a t i o n of Pearce's o r i g i n a l procedure 15 16 and i s c a l l e d the Pearce-low method. R.J. Morgan also uses the a l k a l i  f u s i o n method f o r d i s s o l v i n g t i n ores and f i n d s that  consistent r e s u l t s are obtainable using t h i s process.  J. Gray  has obtained accurate r e s u l t s f o r low grade ores w i t h sodium hydroxide whereas potassium cyanide i s e n t i r e l y u n r e l i a b l e . 9  13 G. M. Henderson used sodium peroxide instead of the g r e a t l y increased. The peroxide was a l s o discussed by J . Gray hydroxide and found that the speed of the a n a l y s i s was who claims i t s advantage over the hydroxide i s only i n s p e c i a l cases, as when chromite i s present.  4 EXTRACTION OF TIN FROM ITS ORES. 1. Occurrence of Samples. Tin  occurs i n Nature i n three forms: (1) as C a s s i t e r i t e  or stannic oxide, (2) as s t a n n i t e , the combined sulphides of Iron, Copper and T i n and (S) as n a t i v e T i n . By f a r the most abundant source of t h i s element i s C a s s i t e r i t e and hence t h i s mineral has been studied i n some detail.  Stannite occurs u s u a l l y i n much smaller q u a n t i t i e s  and o f t e n i n small proportions along w i t h the oxide.  It i s  very seldom used as a souree of T i n not only because of i t s r a r i t y but a l s o because of i t s low t i n content.  Hence i t  has not been studied i n the same d e t a i l . Hence i n e f f e c t i n g the d i s i n t e g r a t i o n of the mineral, the methods already i n use i n connection w i t h C a s s i t e r i t e were t r i e d , and s i m i l a r ones i n the case o f the Stannite. The sample of C a s s i t e r i t e r e f e r r e d to was obtained from the Consolidated Mining and Smelting Company, from t h e i r S u l l i v a n mine, at Kimberley, B. C.  I t had bein  concentrated from t h e i r t a i l i n g s and was a f a i r l y r i c h ore. A sample of Stannite was obtained from the Snowflake mine, s i t u a t e d twenty miles n o r t h o f Revelstoke.  I t was taken  from a quartz v e i n and was of low q u a l i t y . These two ores seemed to f u l f i l l the conditions l a i d down above as to d i f f e r e n c e i n conditions of formation.  5 2  « The D i s i n t e g r a t i o n of O a s a i t e r i t e Sample.  The methods of t r e a t i n g C a s s i t e r i t e are v a r i e d and have 17 13 been aiseussed by H. M i l o n and R. Fouret, and J. Gray. The t i n oxide may be reduced by carbon, hydrogen, i l l u m i n a t i n g gas, z i n c or potassium cyanide. and cyanide were t r i e d .  Of.these carbon  The f i n e l y ground ore was w e l l mixed  w i t h powdered charcoal and placed i n a p o r c e l a i n c r u c i b l e w e l l l i n e d w i t h the reducing agent.  The dross was heated t i l l  redness and kept at t h i s temperature f o r ten minutes.  On  c o o l i n g the reduced t i n was found to e x i s t i n very small p a r t i c l e s which had to be separated by s l u i c i n g . The cyanide method was next t r i e d and since the r e s u l t s obtained i n t h i s ease were most s a t i s f a c t o r y , the p u r s u i t of a b e t t e r method was discontinued.  A 25 gram sample was w e l l  mixed w i t h an equal quantity of Potassium Cyanide and placed i n a 3 i n c h p o r c e l a i n evaporating d i s h .  On both top and bottom  of the mix was placed a l a y e r of pure cyanide.  The c r u c i b l e  was heated, slowly at f i r s t and then more r a p i d l y , u n t i l the whole mass had fused.  The temperature was f i n a l l y r a i s e d to  a b r i g h t red heat and then the c r u c i b l e and i t s contents were allowed to c o o l g r a d u a l l y . about t h i r t y minutes.  The whole operation required  The melt was then leached out w i t h  water and the m e t a l l i c t i n button found on the bottom o f the c r u c i b l e . I t has been noted above that the Pearce Low method of f u s i o n w i t h Sodium Hydroxide gives the most accurate r e s u l t s , e s p e c i a l l y w i t h low grade ores, and seems to be the best method  thus f a r suggested.  While the cyanide f u s i o n i s not an  accurate a n a l y t i c a l method, i t i s r e l a t i v e l y most e f f e c t i v e i n the s e p a r a t i o n of the t i n from other constituents and f o r t h i s reason was adopted. 3. The D i s i n t e g r a t i o n of Stannite. Very l i t t l e study has been made of the d i s i n t e g r a t i o n of s t a n n i t e ores.  A c c o r d i n g l y those methods which are  s u c c e s s f u l i n f u s i n g C a s s i t e r i t e , were also t r i e d w i t h stannite with varied results. A small sample of f i n e l y ground ore was b o i l e d w i t h aqua r e g i a f o r sometime but was not attacked. Potassium n i t r a t e i s a powerful o x i d i z i n g agent and i s often used s u c c e s s f u l l y f o r t h i s purpose.  I n order to test  out the method, f i f t e e n grams o f ore and an equal quantity of the n i t r a t e were w e l l mixed and placed i n a f i r e c l a y c r u c i b l e o f two hundred c c . capacity.  An upper and lower  l a y e r of pure potassium n i t r a t e was used and the c r u c i b l e heated g e n t l y i n a muffle furnace u n t i l f u s i o n .  The temper-  ature was then r a i s e d and maintained at red heat f o r t e n minutes longer.  On eooling the charge was found to have  changed somewhat i n color and appearance, and had become extremely hard and b r i t t l e .  I t was found to be very d i f f i c u l t  to remove by mechanical means, i . e . , w i t h hammer and c h i s e l , and could not be d i s s o l v e d by any of the ordinary a c i d s or aqua r e g i a . unsuccessful.  Therefore t h i s attempt was considered  7 The Cyanide f u s i o n was used i n a manner s i m i l a r to that o u t l i n e d above.  When the cyanide was leached out with water  i n the customary manner, the f i n e l y d i v i d e d ore came out as w e l l , s t i l l i n the form of a f i n e black powder. not been attacked.  The ore had  The duration of the heating p e r i o d a f t e r  f u s i n g d i d not seem to a s s i s t the process of reduction. I t has been already noted that the sodium hydroxide f u s i o n i s the standard method of d i s i n t e g r a t i n g and analysing Cassiterite.  About t h i r t y grams of broken Sodium Hydroxide  was mixed w i t h f i v e grams of f i n e l y d i v i d e d ore and the mixture fused f o r h a l f an hour i n a p o r c e l a i n e r u c i b l e . The melt was f i r s t softened w i t h water and then with  HC1.  The ore d i d not d i s s o l v e even on b o i l i n g . 18 J.H. Walton and H.A.  Scholz found that many r e f r a c t o r y  substances could be e a s i l y decomposed by f u s i o n w i t h Sodium Peroxide.  Their experiments included a Titanium T i n ore.  This method as a p p l i e d to C a s s i t e r i t e has been h i g h l y 13 recommended by Gray. I n g e n e r a l , even where the sodium hydroxide f u s i o n i s s u c c e s s f u l , the peroxide has been found to produce a surer, safer, and more complete fusion, f o r not only i s a better mix p o s s i b l e , but the combined e f f e c t of an o x i d i z i n g and s a l i f i c a t i o n agent i s obtained. Accordingly twenty-five grams of ore were w e l l mixed w i t h an equal quantity of Sodium Peroxide and the mixture t r a n s f e r r e d to a f i r e c l a y c r u c i b l e .  I g n i t i o n of the mix  was obtained by heating gently i n a muffle furnace f o r three  8  or four minutes.  The molten mass was allowed to cool somewhat  and was then poured c a r e f u l l y i n t o about s i x l i t r e s of water. V i o l e n t e b u l l i t i o n took plaee at f i r s t , but soon subsided. The remainder of the melt was and added to the s o l u t i o n .  e a s i l y chipped from the c r u c i b l e  This mixture s t i l l appeared  p a r t i a l l y undecomposed but on a c i d i f y i n g w i t h HC1  and  warming, complete s o l u t i o n was obtained, y i e l d i n g a c l e a r yellow l i q u i d .  To remove s i l i e a t h i s s o l u t i o n was evaporated  u n t i l the l a r g e Jfcl which p r e c i p i t a t e d , became quite v i s c o u s . The mixture was decantation.  then d i l u t e d , and the s i l i c a separated by  The s i l i e a was then f u r t h e r extracted with  d i l u t e H y d r o c h l o r i c a c i d u n t i l the s o l u t i o n obtained was  no  longer y e l l o w . This method of f u s i o n has proven to be quite s a t i s f a c t o r y f o r the d i s i n t e g r a t i o n of s t a n n i t e ore.  I t i s exceedingly  r a p i d and r e q u i r e s only a r e l a t i v e l y small amount of f u s i n g material.  Since the m a t e r i a l i s to be l a t e r p u r i f i e d , another  important feature i s to be noted. would be d i f f i c u l t  No f o r e i g n material which  to remove l a t e r on, i s introduced.  4. P u r i f i c a t i o n of C a s s i t e r i t e T i n . The metal i s obtained from the cyanide f u s i o n i n the form of a shiny button.  A l l the cyanide i s f i r s t c a r e f u l l y  d i s s o l v e d out w i t h water and the metal then d i s s o l v e d by warming i n HC1.  The t i n i s p r e c i p i t a t e d from t h i s s o l u t i o n  as the sulphide by passing i n hydrogen sulphide gas, i r o n and other group (3) metals remaining i n s o l u t i o n .  The  9 p r e c i p i t a t e was f i l t e r e d , washed, and d i s s o l v e d by warming w i t h ammonium p o l y s u l p h i d e .  When copper i s present i n large  q u a n t i t i e s , i t i s d i s s o l v e d to a small extent by t h i s reagent, but  there was no i n d i c a t i o n of i t s presence i n the sulphide  as i t appeared , b r i g h t yellow and p e r f e c t l y homogeneous. The  ammonium sulpho stannate was then f i l t e r e d and the stannic  sulphide r e p r e c i p i t a t e d by a c i d i f y i n g the f i l t r a t e w i t h d i l u t e hydrochloric  acid.  The large yellow p r e c i p i t a t e obtained was  washed f r e e o f a c i d and then treated i n a beaker w i t h eonc. N i t r i c Acid.  Small pieces of yellow amorphous sulphur were l e f t  u n d i s s o l v e d even on warming.  These were f i l t e r e d o f f , washed  and r e j e c t e d , the wash water being added to the main s o l u t i o n . The  s o l u t i o n of the t i n i n n i t r i c a c i d was then evaporated  almost to dryness, a c l e a r transparent j e l being obtained. This j e l gave a f i n e white f l o c c u l e n t p r e c i p i t a t e of metastannio a c i d when a g i t a t e d w i t h a large excess of water.  Dilute  n i t r i e a c i d was added to increase the s o l u b i l i t y of any i m p u r i t i e s and the p r e c i p i t a t e most conveniently f i l t e r e d by decantation.  Antimony forms a corresponding pentoxide which  however i s i n s o l u b l e only a f t e r i g n i t i o n .  Hence t h i s  procedure should remove the l a s t p o s s i b l e traces of any impurities. To obtain the t i n i n a m e t a l l i c form, the p r e c i p i t a t e (H Sn0„) was d i s s o l v e d i n concentrated hydrochloric 2 3 o  d i l u t e d , and e l e c t r o l y s e d .  acid,  As Platinum i s d i s s o l v e d somewhat  by nascent c h l o r i n e , i t was necessary to s u b s t i t u t e some other r e s i s t i v e m a t e r i a l which i s not attacked, f o r an anode.  Tantalum metal i s not attacked, by aqua r e g i a or c h l o r i n e , hence would be quite u s e f u l f o r the purpose.  A  t h i n s t r i p , one mm. i n width and t e n cm. long was obtained, and was s u b s t i t u t e d f o r the anode, and a f i n e platinum rod used as cathode.  The tantalum however, on imposing an E.M.F.,  was found to take on an i r i d e s c e n t  blue f i l m of the oxide,  which was quite impervious to the passage of the current. I t i s remarkable that the current was found t o pass i n the opposite d i r e c t i o n w i t h the tantalum serving as a cathode. A s p e c t r o s c o p i c a l l y pure carbon electrode, f i f t e e n cm. long and one h a l f cm. i n diameter was obtained from Adam H i l g e r L t d . , and s u b s t i t u t e d f o r the anode.  I t was found  to be very s a t i s f a c t o r y and r e s i s t e d the a c t i o n o f the c h l o r i n e quite w e l l .  The platinum rod was again used as  cathode. The t i n deposited i n s h i n i n g l e a f l e t s which were i o l l e c t e d d a i l y and stored i n d i s t i l l e d water.  To obtain i n  a more compact form the c r y s t a l s were placed i n a p o r c e l a i n boat and fused i n a current o f pure dry hydrogen.  A shiny  m e t a l l i c button was obtained. This completed the p u r i f i c a t i o n . The hydrogen f o r t h i s purpose was prepared by the action of zine on s u l p h u r i c a c i d and was p u r i f i e d by passing through a s e r i e s o f wash b o t t l e s containing concentrated a l k a l i , and over hot copper gauze.  11  5. The P u r i f i c a t i o n of Stannite T i n . The percentage of t i n i n t h i s ore i s very much lower than i n the C a s s i t e r i t e .  Hence the procedure had to be  modified considerably, as c e r t a i n separations used i n the preparation  o f pure t i n from C a s s i t e r i t e can not be used  where there i s only a small q u a n t i t y of t i n , and much l a r g e r q u a n t i t i e s of other elements. From the h y d r o c h l o r i c a c i d s o l u t i o n of the ore, the t i n was p r e c i p i t a t e d as the sulphide along w i t h other group (8) metals, the most serious of these being antimony and copper. This p r e c i p i t a t e was f i l t e r e d o f f , washed, and then warmed w i t h ammonium p o l y s u l p h i d e . behind as expected, solution.  Instead of l e a v i n g the copper  quite a l a r g e quantity of i t passed i n t o  This was i n d i c a t e d by the dark c o l o r of the sulphide  p r e c i p i t a t e obtained by a c i d i f y i n g the s o l u t i o n of ammonium sulpho-stannate w i t h d i l u t e h y d r o c h l o r i c a c i d .  The process  o f d i s s o l v i n g i n ammonium polysulphide and p r e c i p i t a t i n g w i t h h y d r o c h l o r i c a c i d was repeated, but there was s t i l l considerable copper present.  Consequently the p r e c i p i t a t e was dissolved  by warming i n d i l u t e n i t r i c a c i d , the sulphur residue f i l t e r e d o f f , and the s o l u t i o n evaporated to dryness.  On d i l u t i n g and  a g i t a t i n g the residue w i t h water, a white f l o c e u l e n t p r e c i p i t a t e of metastannie a c i d appeared.  By evaporating to dryness, i t  was found that some of the antimony was rendered i n s o l u b l e by being converted to the pentoxide.  The evaporation had to  be c a r r i e d that f a r because of the small quantity of t i n  j  IE  present.  However, by t a k i n g up the residue i n a i l u t e n i t r i c  a c i d , the copper and other metals form soluble n i t r a t e s , while the t i n and antimony remain quite i n s o l u b l e . The antimony was then separated by t a k i n g advantage of the f a c t that t i n can not be p r e c i p i t a t e d i n a s o l u t i o n of a c e r t a i n a c i d c o n c e n t r a t i o n i n which the antimony i s r e a d i l y p r e c i p i t a t e d . The i n s o l u b l e residue obtained on evaporation w i t h n i t r i c a c i d was d i s s o l v e d i n concentrated h y d r o c h l o r i c a d d ,  and  the s o l u t i o n d i l u t e d w i t h f i v e times i t s volume of water. The antimony was p r e c i p i t a t e d by s a t u r a t i n g the hot s o l u t i o n w i t h hydrogen sulphide.  The t i n was then obtained as yellow st  stannic sulphide by almost n e u t r a l i z i n g the f i l t r a t e with ammonium hydroxide, d i l u t i n g , ana s a t u r a t i n g the c o l d s o l u t i o n w i t h hydrogen sulphide. II. THE STABILITY OF STANNIC OXIDE. The atomic weight of t i n has been determined by several 19 Investigators  by means of the r a t i o Sn: SnOgjwithout exception  the values obtained by them have been too low, due to absorption of a i r on so l a r g e a surface.  In order to  determine the accuracy of the method as a means of estimating t i n , the temperature of drying and s t a b i l i t y of the oxide to heat treatment was i n v e s t i g a t e d . A small button of C P .  t i n , weighing approximately  one  gram was f i l e d to remove surface oxide and etched w i t h dilute hydrochloric acid.  I t was then washed w i t h d i s t i l l e d  water, d r i e d , and c a r e f u l l y weighed.  The metal was converted  to the oxide "by warming i n cone, n i t r i c a c i d , the excess o f a c i d being c a r e f u l l y evaporated when the metal no longer remained.  The r e s i d u e when d r i e d at d i f f e r e n t temperatures  gave the f o l l o w i n g r e s u l t s . O r i g i n a l weight of Sn button* 0.9923 grams.  A f t e r drying i n the oven f o r two hours, at 150 degrees. A f t e r d r y i n g i n the oven f o r twenty-four hours at 150 degrees. A f t e r h e a t i n g w i t h a b l a s t lamp f o r h a l f an hour A f t e r heating w i t h a b l a s t lamp f o r another h a l f an hour. A f t e r heating w i t h a b l a s t lamp f o r another h a l f an hour.  Weight of Sn0 2  Atomic Weight Calculated.  1.2743  11.6  1.2643  116.73  1.2632  117.21  1.2623  117.60  1.2619  117.78  I t can thus be seen from these measurements that prolonged heating tends to decrease the amount of a i r absorbed, but i t i s doubtful whether a p e r f e c t removal of the absorbed gases can be a t t a i n e d . III.  THE DETERMINATION OF TIN AS CAESIUM CHLORO STANNATE.  T i n forms several complex c h l o r i d e s with the a l k a l i metals, of which the caesium chloro stannate i s i n s o l u b l e . As the o r i g i n a l object of the i n v e s t i g a t i o n was to determine the atomic weight of t i n i n i t s d i f f e r e n t ores, the p o s s i b i l i t y of u s i n g the formation of t h i s s a l t as a method was considered.  The method was i n v e s t i g a t e d i n the f o l l o w i n g manner. P r e p a r a t i o n of Stannic C h l o r i d e . A small button of t i n corresponding to about one gram was f i l e d u n t i l a l l the surface l a y e r had been removed.  It  was then etched i n d i l u t e h y d r o c h l o r i c a c i d and washed i n d i s t i l l e d water.  A f t e r drying and d e s s i e a t i n g , the button  was a c c u r a t e l y weighed.  I t was then d i s s o l v e d i n a covered  beaker i n concentrated h y d r o c h l o r i c a c i d w i t h gentle warming, and the stannous c h l o r i d e o x i d i z e d by passing i n c h l o r i n e , the temperature of the l i q u i d being kept as low as p o s s i b l e by running water.  Previous t e s t s have shown that a corresp-  onding q u a n t i t y of t i n can be o x i d i z e d i n t h i s manner i n h a l f an hour, so i n the present case one hour was considered as s u f f i c i e n t . P r e p a r a t i o n of Caesium C h l o r i d e . The caesium used f o r the purpose was obtained from Dr. E.H. A r c h i b a l d i n the form of caesium sulphate.  I t had  o r i g i n a l l y been used f o r the determination of the atomie weight of caesium.  To convert t h i s m a t e r i a l to caesium  c h l o r i d e the c a l c u l a t e d weight of r e c r y s t a l l l z e d barium c h l o r i d e necessary was added to i t .  The p r e c i p i t a t i o n was  c a r r i e d out i n a t o t a l volume of two l i t r e s and both s o l u t i o n s were kept hot during the mixing. A f t e r s t i r r i n g and d i g e s t i n g the p r e c i p i t a t e f o r sometime, i t was f i l t e r e d o f f and the f i l t r a t e of caesium c h l o r i d e evaporated to a small volume. To remove p o s s i b l e traces of sulphate, the caesium chloride was r e p r e c i p i t a t e d from the s o l u t i o n by s a t u r a t i n g i t w i t h HC1 gas. f o r use.  The c r y s t a l s , a f t e r washing and drying were ready  Method. A s l i g h t excess of the c a l c u l a t e d amount of caesium c h l o r i d e was weighed up and d i s s o l v e d i n twenty-five c c . of water and added a l i t t l e at a time to the stannic c h l o r i d e . The caesium chloro-stannate came down as a f i n e white precipitate.  I t was f i l t e r e d o f f and washed w i t h pure water  i n a tared Sooch c r u c i b l e , which had been prepared w i t h an asbestos mat.  The c r u c i b l e and i t s contents were then d r i e d  i n an oven f o r s e v e r a l hours at 150°G, and weighed. The f i r s t r e s u l t s c a l c u l a t e d from the r a t i o Sn:0s SnGl o  fl  2  o  gave a value f o r the atomic weight of t i n whieh was much too high, i n d i c a t i n g that the weight of the p r e c i p i t a t e was correspondingly low.  Moreover, on evaporating the f i l t r a t e  and wash water a number of c r y s t a l s s e t t l e d out.  As the  f i l t r a t e should contain nothing but a s l i g h t concentration of caesium c h l o r i d e , i t was concluded that the low r e s u l t s could be a t t r i b u t e d to the s o l u b i l i t y o f caesium ehlorostannate. Two more determinations were made taking greater precaution to decrease an e r r o r due to s o l u b i l i t y and more accurate values were obtained.  This j u s t i f i e s the assumption  that the e r r o r i s due at l e a s t i n part to s o l u b i l i t y . As very l i t t l e work has been done on t h i s compound i t was  considered necessary to obtain more d e f i n i t e information  on i t s s o l u b i l i t y i n v a r i o u s concentrations of h y d r o c h l o r i c a c i d and caesium c h l o r i d e . Such information would enable us to s t a t e more d e f i n i t e l y whether t h i s method i s s u i t a b l e or  not f o r atomic weight determinations, and i f so, the most s u i t a b l e concentration f o r p r e c i p i t a t i o n .  Accordingly, t h i s  has c o n s t i t u t e d another phase of the i n v e s t i g a t i o n . IV. THE DETERMINATION OF THE SOLUBILITY OF CAESIUM CHLORO ST ANNATE. Apparatus. I n order to a g i t a t e the s o l u t i o n s at a constant temperature u n t i l the e q u i l i b r i u m of s a t u r a t i o n was obtained, a g r a n i t e k e t t l e of f o r t y l i t r e s capacity was nearly f i l l e d w i t h water and covered w i t h a t h i c k l a y e r of f e l t to prevent radiation.  The water was maintained at constant temperature  by a tungsten lamp which was c o n t r o l l e d by a thermostat and o o relay.  The temperature remained w i t h i n .05  apparatus.  of SO  with t h i s  Pyrex t e s t tubes of twenty-five c c . capacity  were used and rubber stoppers which had been p r e v i o u s l y b o i l e d f o r s e v e r a l hours w i t h ammonium hydroxide. Method of Determination. To the tubes were added twenty-five c c . of s o l u t i o n , and somewhat more of the caesium chlorostannate than would d i s s o l v e i n that p a r t i c u l a r concentration. prepared as i n the determinations above.  The s a l t was The rubber stoppers  were then wired i n and the tubes attached to the s t i r r i n g apparatus and rotated f o r twenty-four hours. In order to determine how much of the s a l t had d i s s o l v e d , the t e s t tube was placed i n the bath so that the top just stood above the water.  A f t e r the excess s o l i d had s e t t l e d  to the bottom, the l i q u i d was drawn up i n t o the c a l i b r a t e d  p i p e t t e and two t e n c.e. p o r t i o n s withdrawn.  The t i p of the  p i p e t t e was prepared by t y i n g a f i l t e r paper around i t w i t h a small piece of s i l k thread.  I n t h i s manner the p o s s i b i l i t y  of s o l i d p a r t i c l e s being drawn o f f was e l i m i n a t e d . The twenty c.e. p o r t i o n s of l i q u i d were c a r e f u l l y evaporated i n small p o r c e l a i n c r u c i b l e s , and the amount d i s s o l v e d taken as the weight of the residue obtained on evaporation. The r e s u l t s as f a r as they have been c a r r i e d at the present time are given i n the f o l l o w i n g t a b l e .  BIBLIOGRAPHY 1.  F. W. Aston,  Uature,  2.  Levol,  Annales de ehimie et de physique (3, t XLIX), page 87.  3.  Moissenet,  Comptes rendus t L I , page 205.  4.  Beringer,  Text Book of A n a l y s i s , page 278.  5.  Hampe,  Chemixer Zeitung 1887, 11-19.  6.  Parry,  The Assay of T i n and Antimony, p.34.  7.  S. Fawns,  Tin Deposits o f the World, page 215.  8.  Bayerlein-Essen,  Z Agnew Chem. 23, 969.  9.  G.M. Henderson,  Eng.  109, 813, (1922).  Min. Journal, 103, 267, 1917.  10. C. Boy,  M e t a l l m E r z 20  11. T. GolieJc,  Eng.  12.  Cortl,  Anal Soe. quim Argentina 9, 44-53 (1921). Chem. Ab. 15, 3801.  13.  J . Gray,  J. Chem. Met. S o c , S. A f r i c a , 10, 402-3.  210-7 (1923).  Min. Journal, 102, 827, 1916.  14. E. 7. Pearee,  T i n Deposits of the World, page 207.  15. Low,  Technical Methods o f Ore A n a l y s i s , page 246.  16. R.J. Morgan,  Chem. Eng. 14 289-91.  17. H. M i l o u and R. Fouret.  Orig. Com. 8th Intern. Cong. Appl. Chem., 1, 373.  18.  J . H. Walton and H.A. Scholz.  Chem. Abs. 2, 2530.  19.  Briscoe,  Journal Chem. Soc. 107, 63, 1915.  

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