84 Journal of the Mitchell Society. [Nov. 



(c) Where calculated the density of the vapor was obtained 

 from the formula, 



[3] D = 0.0 4 16016^, 



where P is the pressure in millimeters of mercury, m is the 

 molecular weight, oxygen equal to 16 as the standard, and T is 

 the absolute temperature. The constant 0.0 4 160I6 was 

 obtained by the use of the values 0.0 4 89873 for the density of 

 hydrogen at 0° C, 760 mm. pressure, latitude 45° and sea level, 

 and0° C = 273° absolute. 



(d) The densities of the vapor given are often carried one 

 place further than the accuracy of the measurements would 

 warrant. This was because the density of the vapor was not 

 always given directly in the original paper, and in the neces- 

 sary transposition the additional figure of the calculation 

 was retained. 



(e) Making use of the well-known thermodynamic equation, 



£ P T 

 W L = j£ -j- (V - v), 



the latent heat of vaporization for methyl, ethyl and propyl 

 alcohols, acetic acid, and ether, were calculated and given 

 in the original papers, where the method in detail may be 

 obtained. The latent heat for water, 0° to 230° C, is from 

 Regnault. The latent heat for benzene, 0° to 270° C, is from 

 Tsuruta, 1 using measurements of Young. 



(_/") In all other cases the latent heats were calculated by 

 the author, the following method being used. Biot's general 

 formula for the vapor pressure, 

 '[5] log P = a + bat + c p^ 



has been found with properly chosen constants accurately to 

 represent the vapor pressure, Differentiating and changing 

 base of the logarithms from natural to Naperian we get: 



[6] Tr = l? (Ho§raa ' + cl °SP^) 



iPhys. Rev. 10,2 (1900). 



