64 PROCEEDINGS OF THE AMERICAN ACADEMY. 



shown in the curves are the values to give the correct change of volume, 

 except at 20°, where O.OjOl was adopted. 



There are a number of measurements of Cp for CS;. Regnault*^ 

 gives 12.68 at -30°, 12.95 at 0°, 13.23 at 30°; Hirn*^ gives 13.13 at 

 30°; Sutherland *7 14.33 at 80°, and 15.22 at 120°; and Forch *» 

 13.34 at 18°. These results are more consistent than usual, lying on a 

 smooth curve within about 1%. Cp increases with rising temperature, 

 the rate of increase also increasing. 



Phosphorus Trichloride. — Two sets of measurements were made 

 on this substance; the first of compressibility and dilatation over the 

 high pressure range, the second over the entire pressure range. Both 

 sets of measurements were made with the smaller high pressure bulb. 

 There was no accident. 



The average discrepancy in the piston displacements for the iso- 

 thermal compressibility at 40° was 0.006 inch on a stroke of about 

 2.0 inches. The discrepancy in the displacement for the dilatation 

 was 0.0011 inch on 0.070 inch, mean. 



The reduction factor from the mathematical formula was 0.9335, 

 showing that PCU is somewhat less compressible than normal. 



The density at 0° and 1 kgm. was taken as 1.612. The three con- 

 stants of the dilatation formula were a = O.O2II39, b = 0.0ol67, and 

 c = O.OsiO.*^ There are also values for the volume of PCI3 by 

 Pierre, who gives for 20°, 40°, and 60°: 1.0231, 1.0477, and 1.0747. 

 The corresponding values computed with the above values for the 

 constants are 1.0234, 1.0485, and 1.0752, rather better agreement than 

 we have come to expect. 



The change of volmne at atmospheric pressure between 1 and 500 

 kgm. was taken from Amagat as 0.0445. Amagat gives for the atmos- 

 pheric volume at 40°, 1.0483, in substantial agreement with 1.0485, 

 given by the formula. At 20° and low pressures, the values found 

 for the change of volume for successive intervals of 500 atmos. were, 

 0.0451, 0.0263, 0.0219, and 0.0187, against the values of Amagat; 

 0.0396, 0.0282, 0.0224, and 0.0186. 



The volume of phosphorus trichloride as a function of pressure and 

 temperature is given in Table XII and in Figure 16. 



There seem to be no other determinations of the initial compressi- 

 bility at atmospheric pressure. Accordingly, the values given in the 



45 Rpgnault, 1. c. (1862). 



46 Hirn, Am. d. chim., 10, 32 (1867). 



47 Sutherland, 1. c. 



48 Forch, Ann. d. Phys., 12, 202 (1903). 



49 Thorpe, Jour. Chem. oc, 63, 273 (1893). 



