K. J. FREDERICK AND j.H. HILDEBRAND
252')
Vol. 60
summary should be negligibly small as long as the co~ice~itration of the water is not great enough to affect 1. Thermodynamic ionization constants of a the properties of the solvent appreciably. From number of indicators atid of acids have been dca large number of experimeiits, a few examples tennined in methanol, aiid the effect of ionic of whch are listed in 'Table ILr, it is seen that the strength studied. presence of 15,; water iii a buffer solution hardl!. 2 . The behavior of the sulfonphthaleins and affects the indicator--buffer equilibrium. tliymolbeiizein is in agreement with modern views 111'Table V is giver1 a sumniary of the values of of their structures. the negative logarithms of the ioiiization C O I I ;;. Iri agreement with Baggesgaard-Rasmusstaiits of iiidicators, pKi, at ail ioiiic strength sei1 and Keimers, it was found that the behavior of of zero. 'l'hc values, iiaturally, arc' i i o more methyl red is best explained on the basis of the reliable than the pK.i values from which they existence of the free amino acid form, and iiot of were calculated. 'l'he ;bKr of 'rropeoliiie 00 has the hybrid form, although the salt effect is not been obtained from expcrimeiits iii dilute hydro- eiitirely accounted for by this interpretation. chloric acid solutioiis i i i niethanol, which will 4. The behavior of other indicators is in agreereported i i i a subsequent puhlicatioii . ment with present concepts. At very small ionic In Table VI is givcii a list of the / J K Avalues strerigths, the salt effect caii be accounted for o f various acids a t ,u := 0, which were calculated quantitatively by t hc limiting Debye-Huckcl from the estrapolatetl pK' \.aluc.s aiid the ~ K Iexpressioi1. values of 'I'ablc V. .\I ISSI?API !l,lS, L I I N S . I 1 ~ r n v ~60, r , , 143li (l!l38). I
melting point was 28-1.I". 'The purified material was enclosed in small Pyrex glass capsules, evacuated before sealing. The capsules had a11 cstcrnal diameter of 12 mm., an internal diameter o f 10 mm., and a length of approximately (icni. 'l'he ratio of weight of tellurium tetrachloride ti 1 weight of glass was about 1.4. 'I'wo differeii( c.apsules were prepared and each oiie was used iri it coiisiderabk iiumher of the runs. The averapr. free space in the capsules was 1.7 cc. Calcula t iotis indicate that the tellurium tetrachloridc \'apor iu the capsules was a negligible factor. Method. -The apparatus aiid method used i i r these determinations were the same as described i i i the account of the work with iodine. Thc higher melting point of the tellurium tetrachloride necessitated further calibration of the thermocouple in the furnace and the melting point of t i i i WSLS used for this purpose. Results and Discussion.-The value of the heat capacity of the calorimeter was 11.3 * 0.4 cal. per degree. Runs on the Pyrex glass used i i i making the capsules showed that its specific heat for tht: interval 2.5-250" cmulrl 1 ) ~ .
Oct., 1938
SPECIFIC HEATSAND
expressed within equation c, = 0.186
f
+ 5.5 X lO-'(t
HEATO F FUSION OF TELLURIUM TETRACHLORIDE2523
0.3% by the
14
+
12 -
- 25)
1.15 X 10-6(t
- 25)*
3
t
The results of the runs made on solid 10 and liquid tellurium tetrachloride are ?given in Table I. The column headed 2 8 H-HZQ8.1 represents the number of calo- X ries evolved in cooling one mole from 3 6 the temperature in the other column down to 25'. The data listed in the 8 4 tables are plotted in Fig. 1. 2 The two values obtained for the solid just below the melting point are ab0 normally high due to some pre-melting. If these two are neglected, the rest of 50 100 150 200 250 Temperature, "C. the results for the solid range follow a Fig. 1. linear relationship within experimental error. The slope of this line is the molal heat ca- tellurium tetrachloride of 55.0 * 0.5 cal. per pacity of solid tellurium tetrachloride in the inter- mole for the interval 224.1-265'. val 25-224.1' and is 33.1 * 0.3 cal. per mole. A The heat of fusion of tellurium tetrachloride at straight line was also found to fit the data for the melting point is 4510 * 30 cal. per mole. liquid tellurium tetrachloride within experimental The entropy of fusion is 9.07 cal. per degree. This error. This gives a molal heat capacity of liquid agrees excellently with the entropies of fusion of silicon tetrachloride, 9.08; titanium tetrachloride, TABLE I 9.00; tin tetrachloride, 9.11; obtained by Latimer.3 H-H298.1 H-Hz98. I , Temp., OC.
cal./moie Solid
Temp.,
OC.
cal./mole Liquid
51.06 71.10 84.32 97.91 116.94 126.72 148.36 168.10 184.63 190.65 204.82 216.10 221'. 60
847.3 1491.3 1920.6 2331.3 3010.3 3399.8 4110.5 4705.5 5263.8 5466.3 5980.5 6410.3 6720.0
226.20 227.80 229.03 233.28 238.63 244.40 249.36 256.85 263.10
11,204.7 11,312.9 11,366.3 11,604.4 11,879.1 12,224.1 12,510.4 12,964.7 13,169.2
Summary Employing the method of mixtures, the heat of fusion of tellurium tetrachloride a t the melting point was found to be 4510 * 30 cal. per mole, the molal heat capacity of solid tellurium tetrachloride in the interval 25-224.1°, 33.1 * 0.3 tal. per mole, and the molal heat capacity of liquid tellurium tetrachloride in the interval 224.1265O, 55.0 =t0.5 cal. per mole. BERKELEY, CALIF.
RECEIVED MAY31, 1938
(3) W. M. Latimer, THISJOURNAL, 44, 90 (1922).
