286 Mr Campbell, 



(3) By precipitation with sodium carbonate and conversion 

 into sulphate as in (2). 



In the case of tin the three methods were : — 



(1) Direct precipitation of tin chloride with hydrogen 

 sulphide. 



(2) Precipitation with potash : solution in hydrochloric acid 

 and precipitation with hydrogen sulphide. 



(8) Precipitation with sodium carbonate and subsequent 

 treatment as in (2). 



As far as is known the solutions from which the salts were 

 derived were not made from the same samples of the metals as 

 those used in testing the activities of the metals. The identity of 

 the properties of samples prepared by different methods seems to 

 be as conclusive a proof as could be given that the activity of the 

 metals is not due to a contained impurity but to an intrinsic 

 activity of the metals themselves. There is only one suggestion 

 that could be made for avoiding this conclusion. It might be that 

 the very small quantity of radio-active impurity that would be 

 required to account for the observed effects might not behave like 

 a true chemical substance but might be dragged down by any 

 precipitate that was formed in the solution. Something of this 

 kind has been observed in the case of the disintegration products 

 of thorium. To ascertain whether such an explanation were 

 possible additional experiments were made. In the case of lead, 

 about one ounce of the sulphate was precipitated from a solution 

 containing four pounds of the acetate : if the activity were due to 

 impurity the whole activity of the solution ought to have been 

 concentrated in the small precipitate. Measurements showed that 

 this was not the case. In the case of tin, calcium chloride was 

 dissolved in the tin solution and sodium sulphate added. The 

 precipitated sulphate showed no abnormal activity. 



10. If similar measurements had been made of the activity of 

 thorium prepared in different ways the activities of the samples 

 might not have been the same, for some of them would have con- 

 tained the thorium X and some would have been free from it. 

 Hence the agreement of the samples in these experiments shows 

 that if there is such a thing as lead X having an activit}^ different 

 from that of lead, it is present in quantities too small to be sepa- 

 rated and detected by this method. This might have been ex- 

 pected, for it is probable that the change of lead is so slow that no 

 sample of it existing on the earth has attained, or nearly attained, 

 radio-active equilibrium *. 



* See Jahrbuch der Radioactivitat, n. 4, p. 459. 



