104 Mr. A. L. Fletcher on the 



of felspathic substances, and is thus o£ quite secondary 

 origin. 



The main object of the determinations given below was to 

 ascertain if any considerable variations in radioactivity were 

 present in the mass of the Leinster granite. The experi- 

 ments, as may be seen, do indeed show a fairly wide range in 

 the quantities detected : from 0*41 gr. per gr. in a specimen 

 of granite taken from the north side of Grlenmalure, 

 Co. Wicklow, to 4*36 x 10~ 12 gr. per gr. in a specimen of 

 granite also from Grlenmalure. 



The fact that the two specimens of highest and lowest 

 radioactivity measured come from the same locality serves to 

 illustrate the sporadic distribution of the radioactive matter. 

 This is borne out by other results. For example, the deter- 

 minations 3*62 x 10~ 12 and 1'76 xl0~ 12 gr. per gr. were 

 made upon specimens taken from points on Killiney Hill 

 within a distance of half a mile of one another. 



Much difficulty has been experienced throughout in pre- 

 paring solutions which are perfectly clear, or such as will 

 retain their limpidity during their period of storage. In 

 some cases the solutions, while showing no visible precipitate, 

 lacked the sparkling appearance, characteristic of perfect 

 solution. 



It did not appear that those determinations made upon 

 solutions containing precipitate fell short of the general mean 

 obtained. In the case of the granite from Aughrim, the acid 

 solution, after a preliminary estimation, was filtered, the 

 precipitate re-fu?ed, and added to the original acid solution, 

 the whole being then reclosed for a further period of storage. 

 A second determination, however, corroborated the first by 

 yielding for the radioactivity nearly the same figure as before. 

 The preparation and estimation of the solutions was carried 

 out in the same manner as before described (Phil. Mag. July 

 1910, p. 36). The same electroscopes were used and the 

 same constants employed. 



In the majority of cases there was no appreciable quantity 

 of radium in the alkaline solutions. As a precaution, however, 

 the alkaline solutions of No. 24 — a mica showing a radio- 

 activity of 4*48 gr. per gr. from its acid solution alone — and 

 of Nos. 1 and 5 in the table, having been treated in the 

 electroscope used exclusively for alkaline solutions, were 

 acidified with hydrochloric acid, reclosed and retested as acid 

 solutions. This confirmed the original result by failing to 

 show any increase in the rate of collapse of the gold-leaf. 



For purposes of accuracy, and to determine whether there 

 were any tendency to a general falling off in the quantity 





