976 Mr. Gervaise Le Bas on the 



theory, for a decrease in the pressure of the gas causes an 

 increase in the coefficient of diffusion of the ions into the 

 gas. It seems reasonable to deduce from the above results 



that, with - not less than 40, and for pressures of 2, 3, 4, 

 p 



and 5 mm., no appreciable number of negative ions can 

 diffuse to the electrodes 1 and 3. 



In conclusion it may be said that no great accuracy is 



claimed for the values of — found in this investigation, but 



p ° 



the experiments show directly the production of positive ions 



by collisions for small values of — and for small potential 



differences between the electrodes, and also give some idea 

 of the distribution of the current in a gas between parallel 

 plate electrodes. 



I desire to express my best thanks to Prof. Townseud, at 

 whose suggestion the investigation was undertaken, for 

 valuable advice given during its progress. 



CIV. The Theory of Molecular Volumes. 

 By Gervaise Le Bas, B.Sc* 



Part III. 



Theory of Partial Rings. 



The Effect of Unsaturation. Residual Affinity. 



(A) a., /3, and y straight Chain Compounds. 



TADEL (Ber. xv. p. 2259, 1889) showed that the 



s 



/3 Halogen compounds always possess smaller volumes 

 than the a, and thus we have examples of molecules supposed 

 to be structurally similar possessing different volumes. 



The cause of this constitutive peculiarity, for it is un- 

 doubtedly such, was not further investigated. 



It is a remarkable fact that the a poly substituted com- 

 pounds all possess volumes which are comparable to those 

 of monosubstituted compounds in that they follow the 

 additive rule. They are thus normal. 



* Communicated by Prof. W. J. Pope, F.E.S. 



