452 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



limit, as we should expect them to do, near the critical temperature, 

 which is about 194° C. But in explanation it is to be noted that the 

 difference between the bracketed and the unbracketed a-columns is much 

 greater in the 198° part of Table XI than it is elsewhere. Indeed, it now 

 seems quite possible that in the unbracketed a-column at 198° the 

 appearance of a maximum value for a in the neighborhood of 700 atmo- 

 spheres external pressure is really significant. If the Ama^at data 

 enabled us to calculate the value of « at 198° through descending stages 

 of pressure to 50 atmospheres, we might find a rapid fall to a value not 

 very different from that which the Ramsay and Young data give for a! 

 near the critical temperature. On the other hand, Table XII seems to 

 indicate a minimum value of a' near 185° C. with a rise from that point 

 on as the critical temperature is approached ; but it is doubtful if the 

 data from which the values of a' have been calculated have sufficient 

 accuracy in the neighborhood of the critical temperature and pressure 

 to allow any importance to be attached to the minimum here suggested. 



The Value of & in Alcohol. 



The values of a given in Table XIII were calculated in the usual 

 way from my data on the compressibility and the expansibility of 

 alcohol. Of these values the first two are for pressures slightly greater 

 than the vapor-pressure, and the last is obtained by using a value of 

 the coefficient of compressibility in the superheated state with a 

 value of the coefficient of expansion in the unsuperheated state. As 

 I have shown that neither of these coefficients is much changed in 

 passing from unsuperheated to superheated state, the above method 

 of getting the value of a at 78° C. causes no serious error. 



TABLE XIII. 



Alcohol. 



The alcohol examined by me contained 0.5 per cent water. So far as 

 the writer is aware, Amagat does not state tlie purity of the alcohol 

 which he used, though it is fair to assume that it contained little water. 



