﻿488 Mr. J. H. J. Poole on the Average 



obtained. It is of course highly improbable that the thorium 

 would be distributed in the way assumed. It is more likely 

 that both the mixture of twelve and of six syenites should 

 have very nearly the same thorium content. It will be seen 

 that the lower result agrees much better with the results 

 obtained for other rocks in the group, and that it also gives 

 a more normal value for the ratio of radium to thorium. 

 It would thus appear that the lower value is the more 

 probable one. 



In order to see whether it was possible that the activity of 

 a solution might go on steadily increasing with time, the 

 following; test was made. A solution containing ten grams 

 of the 23 acid volcanic and intrusive mixture was made up 

 on the 13th of April. This solution was tested on the 20th 

 of April, and again about a fortnight later on the 6th of 

 May. On both occasions it gave a result of 2'2 x 10 ~ 5 . 

 This result would tend to show that the activity o£ a solution 

 becomes constant after the first few days, as one would expect 

 from the rates of decay of the various disintegration pro- 

 ducts involved. To further test the method, the manner of 

 making up the solutions was varied, and the melt from a 

 rock dissolved in its entirety directly in HC], without being- 

 first treated with water. However, the 18 basalts when 

 treated in this way gave nearly the same result as they had 

 given before by the usual method. It was then thought that 

 the limpidity of a solution might possibly affect the ease with 

 which it parts with its emanation. Some of the solutions 

 used in the above experiments were perfectly clear, but a 

 few of them were cloudy owing to the presence of a certain 

 amount of gelatinous silica. One might perhaps suppose 

 that the emanation in the solution might be partially en- 

 trapped in the silica, and so that a cloudy solution would 

 give a lower result than a clear solution. In connexion with 

 this conjecture three solutions each containing five grams of 

 Krakatoa ash were made. One of these solutions was made 

 in the ordinary way, and the resulting solution was rather 

 cloudy. In each of the other two cases two grams of K010 3 

 were added to the fusion mixture. This addition seemed to 

 have a very good effect, as the melt on solution gave a per- 

 fectly limpid solution. In one solution also the amount of 

 HC1 was increased to see if this would affect the result. It 

 will be seen, however, that the three solutions gave practically 

 the same value, indeed the differences are probably within 

 the limits of experimental error for the method. Of the two, 

 the cloudy solution gave the higher result. This may pos- 

 sibly be due to the fact that the presence of a small amount 



