Various Gases by the x Particles of Radium. 351 



a particle inversely, and to a quantity k, constant for any one 

 gas, but varying from gas to gas. It is this quantity which 

 is given in the last column of the tables above. 



The velocity of the a. particle might enter into the formula 

 because A is effective in producing B in proportion to 

 the derangement of the atom or molecule consequent on the 

 presence of the particle within it, and therefore to the time 

 during which the intrusion lasts. There is something odd 

 about this conclusion, which suggests a reconsideration of the 

 position. 



At this stage, therefore, it is natural to raise the question 

 whether the effect A really is the cause of the effect B. 

 whether, that is to say, the energy spent by the a particle goes 

 to the production of ions, or the ionization energy comes from 

 some other source and the a particle merely pulls the trigger 

 in its passage through the molecule. The fact that the 

 ionization produced varies as the time of passage is certainly 

 indicative of the truth of the latter hypothesis ; whilst the 

 occurrence of the stopping-power in the expression for the 

 ionization is not necessarily evidence against it ? because the 

 factor k might be taken in conjunction with s, and ks might be 

 found to represent not some derivative of the energy spent by 

 the particle within the molecule, but some inherent property 

 of the molecule which determined the ionization produced in 

 consequence of the pulling of the trigger. 



The quantity ks represents in the first place the specific 

 ionization of the molecule ; that is a relative measure of the 

 ionization produced in a molecule when an a particle passes 

 through it at a given speed. Now, it is an extraordinary 

 thing that the values of Is which I have obtained for different 

 molecules prove to be nearly related to already well-known 

 molecular constants, such as the molecular volumes, molecular 

 refraction constants, and so on. 



In the following table the values of k, s, and ks of a 

 number of substances are given in the first three columns : 

 the fourth contains the values of the molecular volume r, 

 and the fifth the ratio v/ks. The values of the volumes were 

 for the most part taken from the tables in Ostwald's Lehrbuch 

 der Attgemeinen Chemie, 2nd edition, p. 35b*, <fcc, but those 

 of C 2 H 2 and C 2 H 4 were calculated from the general equation 

 for obtaining the molecular volumes of organic compounds, 

 and the values for C0 2 , 2 , and H 2 were adopted on the 

 assumption that they fell into line with the same equation. 

 This is justifiable since my immediate object is to show a 

 relationship between ks and the atomic volume in combination. 

 As a matter of fact, the molecular volume of 2 per se has 

 been found by Dewar to be 27*1 (Chem. News, June 1898). 



