Radium in Minute Quantities. 711 



the writer i> given in the following table, in which the 

 observed activity for 10 -4 milligrams in each case is raised 

 to 100. 



Quantity of Radium 



in milligrams. Activity (Voller). Activity (Eve). 



10- 4 100 100 



10- 5 53-5 10*6 



10~ 6 51-7 1-18 



10- 7 31 -125 



It will be seen that when the quantity of radium is increased 

 one-thousandfold, Voller finds the activity increased between 

 three and four times, whilst in the present experiment the 

 activity is increased 800 times. 



It appears desirable to remove the impression that the 

 activity of radium in minute quantities decays in a few days. 

 The occurrence of radium in pitchblende refutes such a 

 suggestion. 



It is also desirable to point out that the activity is at least 

 approximately, and is probably accurately, proportional to the 

 ma>> present, and that the properties of a given quantity 

 of radioactive matter are independent of the degree of 

 concentration. 



It must be borne in mind, however, that Voller's experi- 

 ments were carried out on plates exposed to the air, and the 

 writer's experiments were entirely made in a closed vessel. 



No disappearance can be detected in a closed vessel, and 

 therefore Voller's effects cannot be due to the decay of the 

 activity of the radium : but they may indicate a dissipation 

 of the radium itself from the plate. 



Note by Professor E. RUTHERFORD. 



The results given by Mr. Eve in tin- paper are supported 

 by experiments which I have made on the radioactivity of 

 weak radium solutions. A year ago I made up a standard 

 solution of radium bromide containing 10~ 6 milligramsperc.c, 

 which was kept in a stoppered bottle. The quantity of radium 

 in a cubic centimetre of the solution, measured by the amount 

 of emanation produced by it, has not sensibly altered in the 

 course of a year. 



A large number of experiments have been made by different 

 observers on the rate of* decay of the radioactive product-, 

 but in no case has the constant of decay of activity been 



