158 Journal of the Mitchell Society. [Dec. 



ing upon the theory see Jour. Phys. Chem., April, 1902, p. 

 219 and Proc. Chem. Soc, Vol. 17, 233, 1901. 



It appears that at low temperatures, where the vapor pres- 

 sure is small, the results are invariably, and usually very con- 

 siderably, too large. But at the highest temperatures examined 

 for each substance the agreement is good, the divergence at 

 this temperature being- greater than one calorie only in the 

 cases of ether, normal octane, stannic chloride, and four of 

 the five associated substances. 



The results therefore merit detailed study, Of the twenty- 

 one substances, twelve, viz.: ether, di-isopropyl, isopentane, 

 normal pentane, normal hexane, benzene, hexamethylene, 

 fluo-benzene, chlor-benzene, brom-benzene, iodo-benzene, and 

 carbon tetrachloride, give results that are in all respects sim- 

 ilar. With them at the lower temperatures Crompton's 

 theory gives too high results, but as the temperature is raised 

 the results grow in the main continually closer to those given 

 by the thermodynamical equation. For these substances 

 after a vapor pressure of 7000 mms. has been reached, it may 

 be said that Crompton's theory gives a very fair approxima- 

 tion, usually within one calorie, to the results obtained ther- 

 modynamically. 



Di-isobutyl, normal heptane, and normal octane, each show 

 a good agreement at the lowest temperature for which the 

 vapor pressure was measured, viz.; 100°, 80°, and 120°. 

 Then with increasing temperature Crompton's equation gives 

 results lower than those obtained thermodynamically. 



Stannic chloride is similar to the above in showing- better 

 agreement at the lower temperatures than at the hig-her, but 

 in this case Crompton's results are uniformly the larg-er. 



In the case of water the results of Crompton are always the 

 larger, but had the observations been -continued nearer the 

 critical temperature it is quite possible that good agreement 

 would have been reached. 



With the three alcohols, Crompton's equation gives entirely 

 too high results at the lower temperatures. Then with rise 



