1 5 8 Albert P. Mathews 



As already mentioned there is an uncertainty whether 

 the coefficient should be // 3 , as found by Young, or 3 / 20 , as 

 found by Rayleigh. As I was unable to decide which of the 

 values of the coefficient was preferable, I tried them both, 

 and Young's value gives a consistent result. Rayleigh 's 

 gives an impossible result, the cohesive pressure computed 

 by it being more than double what it ought to be, so that 

 if it be substituted in van der Waals' equation, b c must be 

 taken very large and at what are impossible values. For 

 example, b c must be o.748V c , or nearly three-fourths of the 

 critical volume, if the coefficient 3/20 is used. Such a value 

 for "b" is impossible if the atoms retain their uniform size in 

 the molecules, or if they change very little, since the intra- 

 molecular cohesion is so much greater than the intermolecular 

 that the greater part of the gain in volume in coming from 

 zero to the critical temperature must be in the spaces between 

 the molecules, rather than within them. If the atoms are 

 incompressible and make up one-fourth of the total volume, 

 then three-fourths of the critical volume will be free space. 

 If b c = o.75V c and the atomic volume is o.2$V c , then free 

 space within the molecule will be o. 5\ r c , leaving only a total 

 of o.25V c for the inter-molecular space. In other words, the 

 space within the molecules would have enlarged more in pass- 

 ing from zero to the critical temperature than the space be- 

 tween the molecules. Such a result is impossible. With 

 Young's formula, however, b c == o.5V c approximately; if the 

 atomic volume is o.2^V c , then the free space within the mole- 

 cules would be o.25V c and between the molecules, o.5V c , 

 which is a more probable result. 



The following values of M 2 K were obtained by the for- 

 mula, M 2 K = v c X 9-045 X io~ 16 (T c - - 6)/4: 



Substance 



log 10 M'K 



Pentane 



35-7I9I9 



Isopentane 35 . 70663 



Methyl acetate 35 .61791 



Ether -35-67593 



