1904] Mills — Molecular Attraction. 83 



vagaries of a particular molecule cannot of course be followed. 

 But in considering energy relations we commit no error by 

 considering the average molecule as was done. The formula 

 should therefore hold strictly true provided: — 



(a) The molecules are evenly distributed. 



(b) The number of molecules does not change. 



(c) No energy is spent in intramolecular work. 



(d) The attraction does not vary with the temperature. 

 Or, we might sum up a, b, c, and d, by saying that formula 



2 should hold, provided we are dealing with a stable chemical 

 compound whose molecules are not associated. 



The first paper tested the formula so far as the direct 

 measurements of latent heat and the related data permitted. 

 The agreement appeared to be much too close to be the result 

 of accident, but where variations in the data as given by 

 different observers amounted often to five and ten per cent , 

 any close agreement was impossible. It being impracticable 

 to make direct measurements of the latent heat at widely 

 different temperatures, attention was called to the measure- 

 ments of Ramsay and Young and of Dr. Young. These 

 measurements give the vapor pressure and density of liquid 

 and vapor, at corresponding temperatures over a wide range 

 of temperature for thirty-one substances. The present paper 

 deals with twenty-one of these substances, the calculations 

 for the ten esters being not yet completed. 



THE MEASUREMENTS. 



The complete measurements used are given in the appended 

 tables. 



The few exceptions to the following general statements are 

 tioted below. 



(a) The vapor pressure, density of the liquid, and density 

 of the vapor, are from the measurements, references given 

 below, by Professors Ramsay and Young, or Young. 



(b) The vapor pressures from Biot's formula were used in 

 preference to the observed values. 



