80
GEORGE ANTOSOFF
(5) FOWLER, R. H., A N D GUGGENHEIM, E . 4 . : Statistical Thermodynamics, pp. 353-7. Cambridge University Press, London (1939). ( 6 ) GLASSTONE, S.,LAIDLER,K. J., AND EYRING,H.: T h e Theory o j Rate Processes, p. 484 e t seq. McGraw-Hill Book Company, Kew York (1941). (7) KOTTLER, F.: J. Phys. Chem. 47, 277 (1943). ‘(8) MEYER,J., AND ~ I Y L I UB.: S , Z. physik. Chem. 96, 349 (1920). (9) v . 4 ~WIJK, w. R., ASD SEEDER, -4.: Physica 4, 1037 (1937).
w.
DEPU’SITIES OF LIQCIUS AKD THEIR TEMPERATURE CHASGES GEORGE ANTOSOFF
Department o j Chemistry, Fordham University, K e w Y o r k , LVew Y o r k Received J u l y 18, 1943 ISTRODUCTIOX
If one examine> carefully physical constants of liquids as recorded by various authors, one cannot help seeing hon imperfect they are, viz., the diffeience in observations by diffeient author>, or even by the same author, very often largely exceed what may be reasonably ternled the limits of experimental error. time goes on, more and more evidence accumulates that these phenomena are due t o some intrinsic properties of liquids and not to the want of good will on the part of the numerous experimentalists. Of all properties of liquids, densities present the greatest intereit from this point of vie\\ because they can be measured with the utmost accuracy. Thiz paper is restricted t o measurements of density a? a function of temperature, and the material chosen is propyl alcohol. This alcohol is miscible with water in all proportions and therefore it is impossible t o apply t h e method of investigation used for the partially soluble liquids (2) such as isoamyl alcohol. There it I\ a i shou n that 11 ith this alcohol, if it is chemically pure, the difference in propertie. due to pievious history is enormous. Such a system can reach a state of equilibrium \\Len its physical constants attain definite d u e s after a considerable time. CSFCRI.\IESTr\L
The propyl alcohol used \\:is labelled “c.P. normal7’and 11as from Eimer and Amend, Seir Tork. I t 11a- dried v-ith iused potassium carbonate to approximate the conditions under I\ hich Sydney I-oung‘ worked. The reaction with anhydroui copper sulfate sen-ed a5 a criteiion of dryness. S o blue coloration appeared on the addition of copper sulfate to the alcohol after drying, nor is there any at the present time. After drying, the alcohol was distilled. I n order t o protect this alcohol from all possible external influences, it n a s kept in Pyrex g1a.s ( t o avoid the effect of alkalies) and the flask n-as corked. -As, however, 1 In his paper (4) Young mentions two methods (on page 358). One of them, as above, was used for obtaining the experimental data given on page 442.
DEKSITIES O F LIQUIDS AND THEIR TEMPERSTURE CHANGES
81
variations of atmospheric pressure cause penetration of moisture through cork, it was found by the experience of many years that it is better t o establish communication xvith the atmosphere through a tube containing calcium chloride and hanging down so t h a t no dust from it could penetrate into the alcohol. The alcohol was kept in the basement of a big building where the annual variation of temperature is extremely small. During this period no change in density a t 25°C. took place. Densities n-ere measured b e b e e n 25°C. and 90°C. in pycnometers of about 25-ml. capacity. The temperature coefficient of propyl alcohol is small. Per 10°C. i t ehon-s a decrease in density equal t o about 0.0010. Thus the temperature coefficient 16 0.0001
rT=
nhere 6 is the density. The thermostat used n a s so regulated that at room temperature it shon-ed fluctuations not exceeding 0.002"C., and a t higher temperatures the accuracy became about 0 01°C. It is seen that if the variations of temperature nere even as much as 0.1"C.. the effect i.iould be felt only in the fifth decimal place. The pycnometers used n e i e of about 25-ml. citpacity, as alreatlv mentioned, and thus the errors mvoh ecl in 71 eighing on an ordinary analytical balance 11 ould not affect the fourth decimal place in densities. Aille\periments were made in duplicate, i.e., tu o pycnonieteis filled with the same liquid uere handled identically as far aq pocsible u p to the laqt weighing -It each temperature the pycnometerq were kept in the theiino-tat a5 long as na. necewiry t o attain thermal equilibiium. Half an houi appealed to be ample. The expeiimental figures are given in table 1, nhere densities ale given as a function of temperatuie. The column marlied t gi\ the temperatures in degrees Centigrade. Column -1gives the densities observed in a series of experinients immediately follon ing the purification. These data, plotted on graph paper, are given in figure 1. I n the course of 10 days which folloned, a number of similar ciirves 11 ere obtained. I t should be mentioned that accutate timing of these elperiments is haidlj- possible, and in any caw selves no purpose, becaiice these measurements are subject to fluctuations of densities \\ hich niay occur a t the time of nieawrement, or may not. 111 the same, the results nere .nbstantiall>- of the *ame character a- thow in figme 1. For the =.&e of an e v m p l e , in column I3 figiueq for one of these series 316 given. The diffetenceq betneen the figuies of coliinin; -1and R are tabulated in colunin c'. These data are plotted in figure 3, cuive -1, I? is wen that the figures in coinmn B are all a little highel. than those of colutiin -1,and the difference betu een thein slightly exceed9 the limits of espeiimental error. Rut the general character of this curve is the saine as that in figure 1. The same applies t o all other curves of this period and for this reason only one curve, that of figure 1, is given here. The came liquid, n hich stood about siu months under the condition. described above, 11 as taken for a new serie5 of eaperiments. -4s before, tu o pycnometers
82
GEORGE A S T O S O F F
ThBLE 1 Densities of p r o p y l alcohol
I
t
~
_
"C
25 30 35 40 45 50 55
1
I I
60
65 70 75 80 85
~
0 . SO23 0 7963 0 7922 0 7880 0 7839 o 7797 0 7i55 0 7712 0 657O 0 7624 0 7579 0 7536 0 7487
%
I
_
I
C (column 4 column B)
I D
~
_____ ~
0 7966 0 7924 0.7884 0 7841 0 7802 0 7756 0 7715 0 7672 0 7628 0 7579
E
,
-0 0003 -0.0002 -0 0004 -0.0002 -0.0005 -0 0001 -0.0003 -0.0002 -0 0004 0 .oooo
1
I
0 8022 0.7973 0 7932 0 7887 0 7841 0 7798 0.7750 0 7700 0 7651 0.7599 0.7549 0.7492 0.7440
I
(column A column D)
-0.0001 -0.0010 -0.0010 -0 0007 -0.0003 +o 0001 I-0 0003 $0.0012 +o 0019 +o ,0025 +O ,0030 +O .0044 +O 0047
The figures in columns .1and D were obtained by starting a t low temperatures and going gradually upwards. The figures in column B nere obtained in the reversed order, i e., starting a t higher temperatures and going downwards.
SO
40
50 60 70 TEMPERATURE
80
90
FIG.1. Variation of density of propyl alcohol with temperature when measured immediately after purification
DENSITIES O F LIQCIDS I S D THEIR TEJIPERATURE CHASGES
83
were wed within the snnie range of temperatures as above. The deiisities were calculated t o fire decimal places, but there was obserred a small systematic difference between the result? olitained in the tn-o pycnometers, one of them shov-ing
30
40
50
60
70
80
90
TEMPERATURE
FIG.2 . Variation of density of propyl alcohol rrith temperature after sis months
0
+ 00040\
30
40
50 60 70 T E M P E RAT URE
80
FIG.3. Plot of the differences in density changes against temperature. The curve of figure 1, based on data given in column-4 of table 1,is taken as a standard and is represented by the dotted line. The distance between it and corresponding points on curves A and B indicates the actual anioiint of chmge.
84
GEORGE AXTOSOFF
always higher values by approximately one unit in the fourth decimal place, and the fifth figure JYas therefore suppressed. The results given in column D are the average of the two determinations, and thus they are certain within 0.0001. These figures are illustrated by the curve in figure 2, \\-hich is substantially different from the ccrve in figure 1, although there is no change in the initial value a t 25°C. I n column E differences are given betneen the d u e s of columns A and D, and the corresponding curve is given in figure 3, curve B. It is seen that considerable changes took place within the liquid by the time it got into equilibriuni. The curve is more or l e s smooth up to about i5"C., after n-hich there is either a change of curvatwe, or there is an error. Hoxever, each figure is a result of two experiments and neither of them indicated probability of an error. The last tn-o points will be taken up in another series of experiments performed in different conditions more suitable for this range of temperatures. DISCUSSIOS O F RESULTS
The above results s l i o ~ in ! the first place, that bringing of the liquid t o the same temperature does not necessarily lead t o the same result. Complete reproducibility cannot be guaranteed, because the piel-ious history is never exactly the same. Therefore one sometimes observes differences nhich are n-ell above the limits of experimental errors, and ~hilolioften affect, the third decimal place. The accurate timing of these experiments is not possible at, the present stat,e of the subject'. If a Pysteni is not in a state of equilibrium, like tlie freshly distilled liquid, one can wttch the variation of (lensit,>-in a given pycnometer a t a given temperature until the sl-stem gets into equilibrium. Then these fliictuations stop, as was s1ion.n before (3). In these experiments, \\-here densities are nieasurecl against temperatures> differences between similar experiments are t o be expected. I n spite of individual differences these curves all shon- one feature in coninion, viz., they all exhibit a kink in the vicinity of CO'C., just \\-here one can shon- the existence of the kink in the figures of Sydney Toung. This 11-as pointed out hy t.he author long ago (1). There can be no doubt that these kinks, sitiiated a t more or less regular intervals, are not' imsginary. The experimental data are generally given n-ith four decimal places. These effects, hon-ever, need only three places t o be apparent. In this count1.y the general tendency is t o attribute these phenomena to experiniental errors rather than t o correlate them n-ith any intrinsic cause: this is not surprising, as the cwrrent theories do not' take cognizance of these facts. The experiments described v-ere performed a t lox- teniperaturw. Experimental work of this kind becomes more dificult at higher temperatures, not only because it is more dificult t o control the temperature, but also because measurements of vapor densities are involved. -%t!o~>vtemperatures, vhere the vapor is negligible, it is very much easier t o observe the kinks. Thus, for example, benzene s h o w a marked kink a t 45"C'., and everyone can observe it without any elaborate apparatus.
T H E SYSTEM p-TOLUIDIKE-ACETIC
ACID
85
CONCLUSION
The effects described are obviously of the same nature as those observed with isoamyl alcohol (3), Qxceptthat there they were observed in the presence of water. I n such a case the variation of properties of the system lyith time may be due to some tautomeric change within the molecule of alcohol, or to differences in the degree of association between its molecules, or t o some interaction between the two ingredients. The impurities also have t o be considered. I n some cases purification does away with some effects observable in the system. I n the case of isoamyl alcohol these effects are observed only if the sample is chemically pure, because the impurities bring the system t o a state of equilibrium rapidly, exercising a catalytic effect. I n the case of propyl alcohol only two things are possible: viz., either there is tautomerism within the molecule, or molecules react n-ith one another. To the moisture content only a catalytic effect can be attributed. The facts described apparently give the clue to the understanding of the phenomenon of excessive drying. The pre3ence of kinks in the curve n-ould indicate a change in degree of polymerization n i t h the change of temperature. REFEREKCES (1) ANTOYOFF,G . : Phil. X a g . 60, 278 (1925). (2) ASTOSOFF, G., CHANIS,AI., A K D HECHT,A I . : J. Phys. Chem. 46, 487 (1942). (3) ASTOXOFF, G., CHASIS,A I . , ASD HECHT,bI.: J. Phys. Chem. 46, 493 (1942). (4) YOUSG, S.: Sci. Proc. Roy. Dublin SOC.12, 374-443 (1910).
T H E SOLID-LIQL-ID PH-ISE EQL-ILIBRIA O F T H E SYSTElI p-TOLUIDISE-dCETIC *4C'ID WALTER W. LVCASSC, ROBERT P. KOOB,
JOHK G. RlILLER Department of Chemistry and Chemical Engineerzng, University of P e n n s y h a n i a , Philadelphia, Pennsylvania ASD
Receiued December 15, 19.45
Some years ago, following B >tudy (3) of the system aniline-acetic acid in Tvhicli it TI as found that t n o conipoundq TT ere formed, one of them metastable throughout the entire range, O'Connor (4)carried out a qiniilar investigation n i t h acetic acid and the homologues of aniline. The systcm. itiidied uere the 0 - , nj-, and p-toluidines, mesidine, and diniethylaniline, each TI ith acetic acid, and conclusions TT ere dran n relating the nature of the compounds formed t o the -.tructure of the primary aromatic amines. I n the present paper, results are given of a redetermination of the system p-toluidine-acetic acid obtained from observation of the temperature of phase change in contrast T\ ith the analytical method nsed by O'Conno;. of determination of the acid in the equilibrium liquid.
