192 



Hon. E. J. Strutt. On the Badio-adivity of [Feb. 29, 



The present paper gives the results of an examination of certain 

 radio-active materials by this method. 



No new emanation has been recognised. The results have in all 

 cases been attributable to thorium and radium. 



If any emanation decidedly more permanent than that of radium 

 existed in the evolved gas, the method could not fail to detect it. For 

 in every case the activity of the gas was watched until it became 

 comparable with the very small activity due to the walls of the vessel. 

 If a more durable emanation had been present even in small quanti- 

 ties, the proportion of it present would have increased relatively to the 

 radium emanation, and its presence would have become apparent 

 towards the end, by a diminished rate of decay. 



Small quantities of an emanation less durable than that of radium 

 might have escaped detection. For they would have been masked by 

 the much greater quantity of the latter. 



By measuring the rate of leak due to the accumulated emanation 

 from a weighed amount, the proportion of radium present may be 

 estimated. A comparison with the leak due to the emanation of a 

 known weight of radium must of course be made. For this purpose 

 it would be best to weigh out, say, a milligramme of radium bromide, 

 dissolve it in a litre of water, and evaporate a small measured quantity of 

 the solution in a suitable tube. In this way the effect due to a 

 standard quantity could be determined. 



The method of experimenting was as follows : — 



The powdered mineral was placed in a hard-glass combustion tube,, 

 drawn out and sealed at one end, connected to a mercury gas-holder 

 at the other. The mineral was heated to redness, and the gaseous- 

 products collected in the gas-holder. When the evolution of gas had 

 ceased, the point was broken off, and air drawn into the gas-holder, up 

 to a standard volume. 



For measuring the electrical effects, an electroscope was used. This 

 was exhausted, and the gas extracted from the mineral, together with 

 the air, which had been used to make up its volume to a sufficient 

 amount, was admitted. After a few hours, enough for the deposited 

 activity to attain its full value, the rate of leak was read. The day 

 and hour was noted, and the gas was pumped out into a test-tube and 

 stored over mercury. After a sufficient time had elapsed, it was again 

 introduced into the apparatus by means of a syphon gas pipette* and 

 the rate of leak again measured. In the meantime the apparatus had 

 been available for making measurements with other gases. 



In some cases the emanation was initially so strong that it could 

 not be conveniently investigated. In such cases a portion of the gas 

 Avas diluted with air for measuring the rate of decay at first. The 



* The methods of manipulation used in storing and transferring the gases- 

 without loss were those described in Dr. Traveri' book, ' The S f udy of Grases.' 



