Radium in Minute Quantities. 709 



has a life o£ more than a thousand years. He also found that 

 the activity o£ radium thinly distributed over a few square 

 centimetres was not proportional to the mass present, hut had 

 an excess of activity very markedly greater, proportionally, 



in the ease of small quantities. Other observers have found 

 that in the ease of the radioactive substances, and their pro- 

 duets the activity of a given mass is independent of the degree 

 of concentration. 



Some test experiments, made by the present writer, do not 

 give results in agreement with those obtained by Voller, but 

 they are in agreement with the generally accepted theory 

 of radioactivity within the probable limits of experimental 

 error. 



The activity as measured by Voller of a small mass of radium, 

 first dissolved in water, and then evaporated over a small area 

 (1*2 cm.), are given in the following table : — 



Amount of Radium Observed, 



in milligrams. Activity. 



10- :; 38-4 



lO" 4 11-6 



10" 5 &2 



10- 6 6-0 



10~ 7 3-0 



10" 8 2-6 



IIP 9 1*6 



It will be seen that on increasing the 1 amount one million- 

 told the activity was increased, not one million time^but only 

 twenty-four times. -, % 



So also for the duration of the effect, the quantities did not 

 last for several hundred years, but disappeared in a few days, 

 thus : — 



Amount of Radium Days to complete 



in milligram-. disappearance. 



ID-' 126 



in-"' 6J 



ln-' ; 26 



in- 7 17 



in-- n; 



LO" 9 L5 



Whatever may be tin- true explanation of the phenomena 



ved by Voller, the experimental method adopted is very 



unsuitable as a test of the two main points under investigation. 



