486 Mr. C. G. Darwin on the Collisions of 



Similar ratios are obtained for the solubilities of oxygen 

 in glucose solutions. 



It is quite clear in the first place, on osmotic grounds 

 alone, that the activity of the hydrogen ion should be 

 practically unaffected by the inversion of the sucrose to 

 glucose and lsevulose ; and in the second place, that the 

 velocity-constant of the inversion will not be influenced by 

 the change in environment which occurs. 



The increase in the activity of the hydrogen ion may be 

 ascribed to a virtual increase in the concentration of the 

 sulphuric acid, due to the inactivating effect of sucrose 

 molecules upon water molecules. This effect may consist 

 in hydration of the sucrose, and in this case there would 

 be an actual increase in the hydrion concentration in the 

 free water. The water which is thus fixed by the sugar 

 (changing from 10H 2 O to 5 H 2 per sucrose-molecule in 

 the foregoing- series) is not available as a solvent for the 

 hydrogen ion or for gases, nor is it osmotically active. 

 From the data of Jones and Lewis it appears that this 

 water is nevertneless chemically active, since the rate of 

 inversion is proportional to the total water present and not 

 merely to the free water — a fact which is difficult to explain 

 on any supposition other than the above. 



We communicated these results to Professor Lewis, who 

 very kindly suggested that they might be published. 



University College, London. 



XLIV. The Collisions of ct-P articles with Hydrogen JSuclei. 

 By 0. Gr. Darwin, M.A., Fellow and Lecturer of Christ's 

 ?, Cambridge * . 



I. Introduction and Summary. 



IN a series of four papers entitled " On the Collisions o£ 

 a-particles with Light Atoms " in the Philosophical 

 Magazine of June 1919, Sir Ernest Rutherford treated of a 

 long course of experiments he carried out on this subject. 

 The first of these papers f dealt with hydrogen, and he drew 

 several interesting conclusions, the most striking of which 

 was that in these collisions the a-particle and the hydrogen 

 nucleus could not both be regarded as simple point charges. 

 He roughly explained his observations by imagining that 



* Communicated bv the Author. 



t Rutherford, Phil" Mag. xxxvii. p. 538 (1919). 



