322 PROCEEDINGS OF THE AMERICAN ACADEMY 



Thus it is seen that thej internal pressures (Ifv) decrease from a 

 value of nearly 4,000 atm. at zero Centigrade, indefinitely. The same 

 is true of jtt'r', but in neither case are the observations sharp enough 

 to indicate the nature of this variation. Indeed, to co-ordinate all the 

 results, I used the smoothing process fi/v = const. Hence I shall have 

 to sketch the mere trend of the data here involved, by grouping the 

 values fi/v"^ along some mean straight line like .29 (560 — 7^ r^ g) (7^), 

 wherein preference is given to low temperatures. Thus the volume 

 equation takes the form 



_ 2^9(0^^ 



When p :=^ — p', the liquid will boil, and consequently, since v — x 

 remains finite, 7*= 560. This number stands not unreasonably for 

 the absolute boiling point of thymol at the external pressure p', 

 which in the last table is 20 atmospheres. 



12. The question now arises how the result (8) compares with the 

 calorimetric equation 



q + \ pdv = X, 



where X = 25 is at the outset considered constant as to temperature. 



Availing myself of equation (8), expressing pressures in degrees 

 per square centimeter instead of in atmospheres, and remembering 

 that Joule's equivalent is 4.2 X 10'', I find 



/ 



^^ 2 9 F — X 



pdv = ^ X (5Q0- T)X In ^ ... (9) 



Table IV. shows that throughout the interval 0° to 50° 



hi ( V— x) / (v — x) = 1.18 nearly. 



Hence the values of the dissociation energy q are in gram calories, 



0° pdv 



20° 

 40° 



Thus the dissociation energy is small as compared with the expansion 

 energy ; but q increases with temperature which is unreasonable. To 

 explain this discrepancy it is necessary to revert to Table II., supposing 



