82 ROYAL SOCIETY OF CANADA 



radiation of the alpha type, but no evidence of the presence of such rays 

 was obtained from the form of the experimental absorption-ionisation 

 curves, and the conclusion was drawn that if any such radiation was 

 present, it must have been emitted with a velocity considerably less than 

 that possessed by the alpha rays from other well known radioactive sub- 

 stances. 



More recently E. Henriot ^ made an examination of the rays 

 emitted by potassium salts, and while the results of his experiments agree 

 in the main with those of the earlier investigators, they differ from them 

 in that they point to a complete homogeneity in the radiation. For on 

 measuring the ionisation produced by the rays after passing through 

 various layers of tinfoil, he found on plotting the logarithms of the 

 ionisation current for the rays from potassium sulphate and potassium 

 chloride against the thicknesses of tinfoil used that the points all lay on 

 a straight line. 



Henriot, in his paper on the subject, also claims that in the course 

 of his measurements he found some slight evidence of the presence of 

 feebly penetrating rays of the alpha type in the radiation from the 

 potassium salts examined. 



Quite recently an examination was made by Strutt 2 of the amount 

 of helium present in a number of saline minerals, and the results of 

 this examination which are given in Table T 



TABLE I. 



make it clear that the potassium bearing minerals and especially sylvine 

 are rather remarkable for the comparatively great amount of helium 

 which they have been shown to contain. In discussing the origin of the 

 gas Strutt considered that it was altogether improbable that the minute 

 traces of uranium and radium present in sylvine could account for so 

 îrajuch helium, and in view of Campbell and "Wood's discovery of the 

 radioactivity of potassium salts he was led to regard potassium itself as 

 the source of the helium in the saline minerals examined. 



1 Henriot, Comptes Rendus, 148, pp. 910-912, 1909. 



2 Strutt, Proc. Roy. Soc, Series A, Vol. 87, No. A 547, p. 278. 



