184 Latent Heat and Surface Energy — Cohesion. 



and if Hammick's chain of deductions from Bakker's rule 

 is sound, Mills's formula must presumably be abandoned. 

 Has Bakker's formula been thoroughly supported by 

 experimental results ? 



S^From Hammick's values for a, I deduce a new modi- 

 fication of the Van der Waals' molecular pressure coefficient 

 for temperatures below the critical if not also above it : 



where a c is the value at critical temperature T c . 

 This is based on two approximations 



— ^- =1'4 (Hammick, loc. cit.), 



a c 



t~ ==1*5 (see Young's tables in ' Stoichiometry '), 



■*-b.p 



whence a c , diminishing linearly, vanishes at T = 2T C . 



and <^abs. zero = - ( 2c' 



Incidentally this leads to a molecular pressure per unit 

 molecular area ^d? cc d~ n , where n is more than 4 (and 

 apparently less than 7), which compares interestingly with 

 "central force" approximations to electron doublet mutual 



attractions. The Clausius-Berthelot form for a, ™-, makes 



a and n = co at absolute zero, which seems absurd. 



In my article (Phil. Mag. ser. 6, vol. xl. No. 236, August 

 1920) on "Cohesion," p. 216, line 15, "three" should of 

 course read " five." 



I take this opportunity of remarking that the principal 

 objection to my formula for molecular attraction is its 

 quantitative deficiency in the vapour state, which I have 

 attempted to explain by cumulative impulses [Proc. Phys. 

 Soc. Lond. vol. xxx. pt. 3, April 15, 1918— " Cohesion " 

 (Fourth Paper)]. 



The anomaly of a temperature function being included 

 in the molecular pressure term in the equation of state may 

 perhaps be explained by the fact that the equation corre- 

 sponds to isothermal changes, and the absorption of energy 

 suggests that additional repulsion may be produced as distinct 

 from diminished attraction. 



This may be absent in adiabatic change and the molecular 

 pressure term would then be in Van der Waals' original form. 



Yours faithfully, 

 Harbour Investigation Office, HERBERT ChATLEY. 



Huangpu Conservancy Board. 

 Shanghai. 

 16.xii.1920, 



