332
A.
w. DAVIDSOK,
K. J. LRGERSINGCR, JR., .WD
c'.
I. MICHAELIS
THE CRYOSCOPIC BEHAVIOR OF CARBOX TETRACHLORIDE' AKTHI-R lv. i j i \ I I M I Y , I\. ,J. = ~ K C ; E A ~ I L \ ( ; EJR I, ,~
C L ~ I1., m ( - r I k m w
1 ) e p u t t ) n w i f o f C ' h m n i s f i i i . 1 n i i r i s i t i l of liniicnn, Lnir/cnrt!. Kon,ws
1ZecLLctd
,/illy
24, 1947
In the course of a series of investigations, now in progress in this laboratory, of phase equilibria in systems consisting of pairs of organic compounds (4, 22), our attention has been attracted to the distinctly unusual course of those portions of the temperature-concentration curves in which the solid phase is crystalline carbon tetrachloride. These are notem-orthy not only for their steep slopes and for their complete lack of the downward concavity usually observed in freezingpoint curves, but also for the strikingly sharp break, or change in slope, which they exhibit at a temperature in the neighborhood of -48°C. Both of these peciiliarities have, it is true, been observed previously. Carbon tetrachloride has been conspicuous, among the common solvents, for its unusually high cryoscopic constant, while the break in its freezing-point curves has been commented on especially by Wyatt (23), who has correctly attributed it to a transition between the tn-o crystalline modifications of carbon tetrachloride. Since, hoIvever, up to the present scarcely more than qualitative explanations (20) have been offered for these facts, it appeared n-orth while to attempt a quantitative interpretation of the freezing-point data jn terms of the theory of the ideal solution. Such an interpretation is indeed scarcely possible in the case of the system carbon tetrachloride-acetone as described by Wyatt, since his data are presented in graphical form only. But for the systems carbon tetrachloride-chloroform (figure 1) as reported by Kanolt (9) and by Sameshima and Hiramatsu (Is),carbon tetrachloride-carbon disulfide as reported by Timmermans (ZO), and carbon tetrachloride-2,6 lutidine (figure 2 ) as studied in this laboratory ( 2 2 ) , application of solution theory brings out an interesting concordance between the experimental data and the temperature-concentration curve as calculated from the Schrbder-LeChatelier equation, as will be shown below. The existence of tn-o solid modifications of carbon tetrachloride was first suggested by Tarnmann ac, early as 1898 (19) and was again pointed out by Goldschmidt (6). McCullough and Phipps (11) characterize the high- and lowtemperature forms as cubic and monoclinic, respectively, and even suggest, as do ,Johnston and Long (8),the possible usefulness of the transition temperature as a fixed point in thermometry. Severthelesq this transition point was overlooked, curiously exiough, in h t h of the studies cited above of the carbon tetrachloridechloroform system.
'
- 24.2"C. .Among there the most dependahlc vtilue, from the ~ t a r i t l p o i n tboth of purity oi material and of aocw acy of tempei ature mw;.urement, appears to be the recent one of H i c k , Hoolcy, and Stephenson ( T ) , -22.0"('. OY 250.3"Ii.; which we shall use in thir discussion. 'The re
