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The vapor pressure of acetone at low temperatures Ure, William 1924

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THE VAPOR PRESSURE OF ACETONE AT LOW TEMPERATURES. by William Ure THE VAPOR PRESSURE OF ACETONE AT LOW TEMPERATURES. by William Ure A Thesis submitted for the Degrée of Master of Applied Science in the Department of Chemistry The University of British Columbia April, 1924. Content8 A* âge I* Introduction...... • 1 II. Expérimental (a) Method X (b) Purification of Materials ••• 2 1. Aoetone 2. Benzène 3. Mercury (o) Thermometer •••••*•*••••• •••••••• 4 (d) Apparatus and Keasureraents.. • *•• 5 III Résulta 9 IV. Latent Heat of Vaporization • .«11 7* Stunmary. • ••••••••••••••12 VI. Bibliography. •• •• • ••••14 Tables, Figures etc. Table 1 10 Table I I 11 Table I I I • 12 P l a t e I to face 5 P i g . l » " 5 F igs . 2 & 3 * " 7 Pig.4 10 THE VAPOR PRESSURE OF ACETONE AT LOT,Y TEMPERATURES. I. Introduction. Efo measurements of the vapor pressure of aoetone below 20*C are available up to the présent time with the exception of two isolated figures at -.59* and -78* by O.Stern, publish-ed in the Tables de Constantes. Above 20° the vapor-pressure 2 3 has been measured by Regnault, and Ramsay and Young. In conjunction with measurements which hâve just been made on the 4 àensity and viscosity of acétone at low températures, it was thought that it would be of value to obtain the vapor-pressure curve of acétone from *20 C down to the freezing point -94.6 C. I I . Expérimental (a) Method. The static method was used, with a différentiel tensimetei in which the différence in pressure in vacuo betv/een that of acétone and a standard liquid was measured by the différence of ]œvel of mercury in a manorneter. It v/as intended at first to use ethyl alcohol as a standard of vapor pressure, dehydra-ting it by means of lime, but it v/as difficult to get out the x Jahresb. Sehies. (Jes. Vaterl. Kult. 19±;>, 90. 29 | Mem.de lUoad. 26. 539. 1862. J Phil.Trans. 178 A 313, 1887. The author, Undergraduate Thesis, 1923. 2 laet trace of water, and to prevent the alcohol absorbing v/ater while being handled, henc?,this was given up, and benzène was uaed instead. Some very pure benzène was avail-able and thie would not absorb water so readily, Mercury was used as a gauge liquid, although it was originally intended to use a liquid of lower spécifie gravity for greater accuracy. It was difficult, however, to find a liquid of the de8lred spécifie gravity, such that the appara-tue would not be unwieldy and at the same time a liquid v/hich would not dissolve or act upon either the acétone or the benzène. (b) Purification of Materials. •* I •• Il • — •••• III U«BM||I—IIIMIIIlll...—^1 — Il I m u — — — — — « — — • — • P I » 1. Acétone - The acétone was purified by crystallization with sodium iodide after the method of Shipsejr" and Werner, as follows: 500 oc. of O.P.acétone were distilled once with a still head. 100 gms. of anhydrous sodium iodide were dissolved in the fresh distillate by heating gently on a water bath. The solution was then cooled to about -20* in ethyl acétate and carbon dioxide snow. The crystale of the compound NaIooNcHj whioh separated out were drained off so far as possible from the mother liquor, quiokly transferred to a dry flask attached 1 J.Chem.Soo. 103-1255. 1?13 3 to a condenser and receiver, and the acétone rapidly distilled Off by sentie heating, The mother liquor was treated with a fnrther quantity of DTal and the prooess repeated until about 230 ce. of distilled acétone were obtained. This quantity was dried with calcium chloride for a day or so and then distilled. The product had a spécifie gravity at 20 , as measured "by pyk-nometer, of .79170, and a refractive index of 1.3397» (D line) Iandolt1^ives for p*! = .7917 and Korten? n^ = 1.3393 so that the aoetone obtained was very pure. 2. Benzène. 300 ce. of G.P. benzène were treated with 23 oo. concen-trated HgSO^ . and the mixture shaken up three times a day, the acid being changed every two days. The benzène was treated with three separate portions of concentrated HoSO,. Àfter this treatrnent the benzène gave no violet coloration (for thiophene) with isatin. The benzène was then separated from the ecid and treated with 200 ce. of distilled water. The mixture ?/as neutralizeô with sodium carbonate, and the benzène washed three times with distilled water. It was then separated from the water and refluxed over sodium for about 4 hours. The benzène was then distilled twice. The product had a spécifie gravity of .87900 at 20° ( pykn orne ter). Young^ gives ifo = .8790. 1 Pogg. 122. 545. 2 Dise. Bonn. 1890. 3 Dublin Proc. 12. 374. 1910. 4 3» Hercury. Mercury was used which had previcusly been distilled twice It was further distilled in vacuo with a smali amount of air bubbling through it to oxidize any base metals , after the 1 method suggested by Hulett. (G) Thermometer» The températures were measured with a platinum résistance thermometer of the bridge type, Leeds & Northrup lue ter Bridge Bo.4201 being used, reading to .0001 ohm, corresponding to * about .01 C. The résistance élément was contained in a quarts tube which also contained gold compensating leads. The galvan-ometer v/as set on a eolid pillar and observed with a lamp and scale. The résistance of the leads was elirninated by takirig the mean of two readings at opposite positions of a commutâtor switch. The thermometer v/as standardized by the Bureau of Stan-dards in Septeraber, 1923, and o in the Gallendar équation found to be l.jjO. On installation the thermometer was checked o a t 0 C and observat ions rnade at the températures of e ther and so l id carbon dioxide (-78.34 C a t atmospheric pressure) o and boiling oxygen (-182.93 G), to détermine the déviations from the parabolio formula. Ât -?8.34 the thermometer read « • o .04 low, and at -182.93, 1.77 low. Thèse values correspond Phys. Rev. 33. 1911, 30?• 5 to Hennings1 corrections to the par&bolic formula» a n d thèse corrections v/ere aocordingly uséd. A chart of résistance against température v/as plotted and used to est.imate the températures at v/hich the vapor pressure measurements v/ere made. (d) Apparatus and Measurements. Fig.l shows the tensirneter v/hich v/as made of' soft glass. The bulbe were filled with acétone and benzène and v/ere direct-ly connected to the manometer arme, Great difficulty v/as experienced in getting ail of the air out of the apparatus, and the following procédure was finally adopted. The manometer v/as filled with the required amount of raercury and the whole appar-atus evacuated through tubes oc, the bulbe bb being closed without filling with liquid. At the saine tirae the mercury v/as heated to boiling to drive out enclosed air. For évacuation the tubes ce v/ere connected through a T tube to an oil pump. Between this and the apparatus, v/as connected a trap immersed in liquid air for the purpose of reÈaining any volatile ingrédients of the oil and of preventing the vapors from the apparatus from impairing the efficiency of the pump. Médium oil of the best grade v/as used, and v/as previously heated to 1,50 . At first a pressure gauge v/as connected in the System but it v/as found that the pump v/ould reduce the pressure to less than one millimeter, so this was left out to minirnize the dangez Ann.der Physik, 40, 1?1J. "PUre I c o °~ aJ c O F.s I. 6 leaks. With this type of apparatus it is not neeessary to reduce to a high degree of vacuum since the residual pressure is equalized on "both sides of the manometer. Less than one millimeter pressure is therefore sufficient. After the mercury has reached "boiling»the apparatus was allowed to cool and then air readmitted through ce. The bulbs were then opened at x,x filled v;ith the liquids and sealed off. The bulbs were then immersed in liquid air and the apparatus évacuâted as hefore for half an hour with the benzène and the acétone both solid and exerting very low vapor-pressures. The mercury was heated again to some extent. The apparatus v/as then sealed off from the purap at ce. To test for the présence of air the tensimeter was set up and meaaurements made of vapor pressure at 20 , the attempt being made to check with Regnault»s resuit of 17?.65 mm. After this first évacuation the measurement obtained was jj cm. too high. This v/as believed to be due to the solution of a certain amount of air in the acétone at atmospheric pressure. This would be retained on freezing in spite of the lowered pressure and v/ould be liberated on warming up in vaouo. This vlew was upheld by the faot that on immersion of the bulbe in liquid air there was still a différence in level of meroury of about 4 cm. The apparatus was therefore opened at oc and re-evacuated, then sealed off. The vapor-pressure as measured at 20° was still a little higher than Regnault»s 7 resuit, but it was believed that this was not air, and a séries of measurements. v/as made. In mailing measurements the apparatus was set up as shov/n in Plate I. The manometer v/as immersed in the glass-sided thermostat, the température of which v/as kept at 25 to within 1/5 by means of a heating bulb B and a toluène regulator H operating an electro-magnetic relay. The thermostat was stir-red by the zig-zag stirrer K, run by the motor M. The benzène bulb v/as immersed in a Dewar flask A, and v/as kept at 0 in ice and distilled water. The température of this bath could be kept constant to within.1*. It was stirred by the glass propellor P. The acétone bulb was contained in the large Dewar flask D which was about 10 cm. diameter by JO cm. long inside dimen-sions. This was the low température bath, and at températures below zéro, ethyl ether was used as a médium and v/as stirred by the double propellor P. Above zéro,water v/as used in this bath and the température regulated by means of hot v/ater or ice to v/ithin .02 . For measurements from 0 to -75 solid carbon dioxide v/as used to lov/er and regulate the température. This was added by hand, and in addition a tube T immersed in the bath v/as partly filled with the snow. This served to hold the température dov/n, although the actual régulation v/as done by the addition of small amounts of carbon dioxide at intervais, Below -75*t liquid air v/as used as a cooling agent. This was contained in a small Dev/ar flask as shov/n in fig. 2 and was 8 used after the manner devised by Henning. Liquid air v/as forced directly into the eïher in flask D by the hydrostatic head in the cylinder d. The depth of immersion of the tube t could be varied and hence the quantity of liquid air forced into the bath varied until it just eompensated for the heat absorbed by the bath* Below 0 the température could be kept constant to within • 2° and the readings in ail cases were taken at zéro deflection of the galvanometer, indicating that the bath was exactly at the desired température. The thermometer is shown at t. Readings were made by means of a cathetometer set at four feet from the apparatus, equipped with a métal scale and vernier reading to .005 cm. Readings were taken approxiraately every five degrees from *20 to -105 . In most cases it was possible to get consistent results to within .005 cm. The benzène at 0 was kept in the metas table liquid p form, and Young*s value for the vapor-pressure at this temp-érature vas accepted. (p s 26.54 mm.) In order to corroborate the values thus obtained a direct reading apparatus v/as constructed, and is shown in fig. 3* This consisted of an acétone bulb directly connected to a small manometer m. The manometer v/as first constructed and 1 Ztschr. Instrumentkunde 33. 1913. 33* 2 J.Chem.Soe. 55-486-1889. 5 > . fi lied and then attached to the îmrb which was filled. The apparatus was evacuated through o with the huit iramerseè in ethyl aoetate and carbon dioxide at about -78 , the small amount of vapor présent at that température serving to sweep out any residual air. It v/as then sealed off at 0. A séries of readings were taken, then the apparatus was opened and re-evaeuated, after which the résulte were found to agrée with those taken after the first évacuation» The resuits obtained with this type of apparatus agreed very closely with those obtained with the other frora 420 to.-25 as shown in Table I. Owing to the difficulté of making an accurate manometer, the latter resuits are taken as more reliable. III. Résulte. The vapor pressures of acétone from +20 C to -105 are shown in Tablé I.I« Pressures are espressed in rnillimeters of mercury at OC, to obtain which, the obeerved height of mercury at 25 was multi-olied by 13*5340 which is the ratio of the 13-5955 . densities of mercury at 25 and 0 . The values are given to two places of décimais. They are reliable to within .1 mm. and are probably correct to .05 mm. The températures are expressed in both Centigrade and absolute degrees.and are given to hundredths of a degree s in ce at the higher tempera-tures .01 corresponds to a change in pressure of over .05 mm. 10 Table I . Cen t ig r ade Abso lu te Yapor - P r e s s u r e Temp. 0 19.89 14 .87 9 .87 4 .82 0 - 5 . 1 5 —10 .1s - 1 5 . 1 5 - 2 0 . 2 1 -25 .07 -30 .07 - 3 4 . 9 6 -39 .89 - 4 4 . 8 1 - 4 9 . 6 2 - 5 4 . 5 3 -59 .47 -64 .57 - 6 9 . 4 4 - 7 4 . 4 1 - 7 9 . 4 0 - 8 4 . 3 5 - 8 9 . 5 2 -94 .35 —99.84 -104 .75 Temp 292.89° 287.87 282.87 277*82 273.00 267.35 262.85 257.85 252.79 247.93 242.93 238.04 2 3 3 . l l 228.19 223.38 218.47 213.53 208.43 203.56 198.59 193.60 188.65 183.48 178.65 173.16 168.25 mm, Hg. I 185.57 150.00 119.42 94.09 75 .25 57.90 44.96 34 .80 26.79 20 .91 16 .13 12 .35 9.86 7.77 6.33 5 .13 4 .29 3.59 3.09 2.59 2.20 1.95 I . 6 5 1.40 1.15 .85 a t 0 0 . I I I 8 6 . 8 5 150.02 119.46 93.93 75 .23 58.23 45 .15 34 .85 26.85 21.10 Column I I shows t h e measurements made w i t h t h e d i r e c t a p p a r a t u s a t t e m p é r a t u r e s t 20° to - 2 5 ° . The agreement on the whole i s ve ry good, and j u s t i f i e s the accep tanoe of t h e r e s u l t s o b t a i n e d w i t h the t e n s i m e t e r . ]pig. 4 shov/s t h e v a p o r - p r e s s u r e curve of a c é t o n e , ob t a ined by p l o t t i n g the observed v a p o r - p r e s s u r e s a g a i n s t t e m p é r a t u r e . A very smooth curve i s o b t a i n e d from t h e expé r imen ta l p o i n t s . o I t i s to be rioticed t h a t t h e p o i n t a t -99 .84 f a l l s on t h e 2 3 5 'Abs + ZO ° C 11 a oon t in f l a t ion of the smooth curve n a s t the f r e e z i n g p o i n t - 9 4 . 6 i n d i c a t i n ? th&t the a c é t o n e wss a s n ^ e r - c o o l e d l i q u i d a t t h a t t e m p é r a t u r e . At -104 .73 the acé tone y/as seen to be s o l i d , and t h i s p o i n t f a l l s av/ay frorn the curve as v/culd be expec t ed . The l i f f e r e r j t i a l équa t ion of t h i s ourve i s t h e C l a u s i u s -Clapeyron équa t ion d lnp m kj dT HT2 where t> is the latent heat of vaporisation and varies with the température. Table II shows the résulta obtained by other investigators v/ithln this température ran«?e, conpared with those obtained in this research. The latter values are obtained from the curve. The results do not agrée, and it is to be noticed that the value obtained at 20 in this v/ork lies betv/een those of the other investigators. Table II» P r e s s u r e as deterrr.ined by Ternp. C Ttegnault Rarnsay & Young S te rn Tire T 2 0 179.63 l?l»9 ' 186.7 -39 1.3 4 .3 -78 0 0 2 ^ IV. L a t e n t Heat of V a p o r i s a t i o n . The l a t e n t hea t of v a p o r i s a t i o n of acé tone nuxy be c a l c u l -a t e d from the d a t a ob ta ined and t h e Olaus ius -Clapeyron é q u a t i o n d lnp B <cj dT ' HT2 i n whioh lnp i s t he n a t u r a l logar i thrn of the v a p o r - p r e s s u r e , Q the h e a t of v a p o r i z a t i o n in c a l o r i e s p e r gram-molecule , 12 T the absolute température and R the gas constant (I.985). If Q is assumed constant over a certain range of tempér-ature the above équation may be integrated to give •Q = 4.571 T 2 T l log.1n P2 V Tx 10 P1 where f^ T-^  and PgTg a r e oorresponding quantities, and Q is the average latent heat over the interval from T to T . In this way the average latent heat was calculated over the ranges of température *20° to -20°C, -20° to -60", and -60 to -90 . Table III shows thèse values expressed in calories per gram of liquid. It is to be noticed that the latent heat of vaporization of acétone deoreases as the température is lower-ed, which is the opposite to that of v/ater and most liquids. This was noticed by Regnault at températures above zéro. At 0* he found the value to be 139.90 oal. , at f-80 , 166.51 cal. and at 140°, 181.69 cal. Table III. Temp.range Latent Heat of Vaporization 1*20*0 to -20 122.18 cal./gm. -20 to -60 86.11 -60 to -90 42.59 V. Summary 1. Pure acétone has been prepared by crystallization with 1 Ànn.Chim.Phys. (3) 26, 278 - 1849 13 sodium iodide a f t e r the method of Shipsey and Werner. 2. The d i f f e r e n t i a l t ens ime t r i c method has "been suocessfully applied to measuring the vapor-pressure of a pure l i q u i d . 3» The vapor-pressure of acétone has been measured from f 20° C to -105* G. 4. The latent heat of vaporization of acétone has been cal-oulated from the observed vapor-pressures over différent O O température ranges from *20 C to -90 • In conclusion I wish to express my thanks to Ur.E.H. Àrchibald for his never-failing advioe and assistance, and to Ihe lesearoh Couneil of Canada for its financial assistance in oarrying on this work. Department of Ohemistry. 14 Bibllography. Hennin5, P. Annalen der Physik 40, 1913. Zeitschrift Instruraentl.ur.de 33, 1913, 33. Hulett Physical rteview, 33, 1911, 307. Landolt Pogg. Ann. 122. 343. Korten Dlss. Bonn. 1890. Ramsay & Young Philosophical ïransactions 178 A, 313» 1887• Regnault Annales de Chimie et de Physique, (3),26,278,1849. LIem. de UAcad. 26, 339, 1862. Shipsey and V/erner Journal of the Chemical Society, 103, 1233, 1913. Stem, 0. Jahreeb Schles. Ses, Vaterl.Kult. 1913, 90, 29. Ure, ïï. Undergraduate Thesis, B.C. 1923. Young, S. Journal of the Chemical Society, 5K). 486» 1889. Dublin Proo. 12, 374, 1910. 


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