194 Hon. E. J. Strutt. On the Radio-activity of [Feb. 29, 



Air drawn over it in the cold possesses strong discharging power. It 

 was not permissible to heat the specimen, which might have injured it, 

 so that the presence or absence of radium emanation in thorite could 

 not be investigated. 



There can be no doubt that the other specimens of monazite 

 contained thorium, for they were given me by the late Mr. W. 

 Shapleigh, who was connected with the thorium industry, and used 

 these varieties of monazite for preparing thoria. They were, moreover, 

 markedly radio-active, while the amount of radium emanation obtained 

 from them was so small that their activity could not be mainly due to 

 radium. They probably contain the thorium in what Eutherford and 

 Soddy call the de-emanated condition. That is, the thorium emana- 

 tion, though formed, is not able to escape. 



It is a remarkable fact that these varieties of monazite, though they 

 contain practically no radium, yield helium in fair quantity. There 

 are several explanations possible. The radium originally present may 

 have almost completely decayed into helium, and any other products 

 which it may yield; or it may be that thorium, as well as radium, 

 yields helium by its decomposition • or, lastly, the helium may not, in 

 this instance, have been generated by radio-active changes at all. 



It is interesting to know whether the minerals retain all the radium 

 emanation which they generate when heat is not used to expel it. Two 

 cases were examined. One hundred and fourteen grammes of powdered 

 samarskite were kept for 3 weeks in a sealed glass tube. The air was 

 pumped out and tested. It was found to contain about yi>~q P a1 ^ °f 

 the emanation, which could have been extracted by heat. 



A similar experiment with malacone showed that about one-fiftieth 

 of its emanation was able to escape in the cold. 



It appears, therefore, that these minerals retain nearly all their 

 emanation. The same is probably true of the helium produced by the 

 emanation. Samarskite which had been heated to redness was found 

 to retain its emanation in the cold about as well as before. 



Part II. 



I happened to possess a small sample of a red deposit, coloured by 

 iron, which is left by the water of the King's Spring, at Bath. It 

 occurred to me that it might be worth while to test this for radio- 

 activity. The result was to show that the deposit was markedly 

 active. On leaving it in the testing vessel (which was closed airtight) 

 for a few days, the activity was found to increase to several times its 

 initial value. This shows that the deposit gives off an emanation 

 freely, even without heat. 



Experiments were then made to test the rate of decay of this 



