Adams — Absence of Helium from Carnotite. 321 



Art. XXXIIL— On the Absence of Helium from Carnotite ; 

 by E. P. Adams. 



The experiments of Sir William Ramsay and Soddy on the 

 formation of helium from the radium emanation account very 

 readily for the well-known fact that the minerals which con- 

 tain helium in appreciable quantity contain as well one or more 

 of the radio-active elements. It might therefore be expected 

 that all radio-active minerals should contain helium. 



I have recently been testing various specimens of carnotite 

 to determine whether or not helium is present in them. Car- 

 notite promises to become an important source of radium ; cer- 

 tain specimens have been found which have a radio-activity 

 1*6 times that of metallic uranium, although it appears to be 

 difficult to obtain large quantities of mineral of such high 

 activity. On heating in vacuo several grams of this carnotite, 

 considerable quantities of carbon dioxide and water were driven 

 off, and when these were absorbed by caustic potash and phos- 

 phorus pentoxide respectively, only the nitrogen spectrum 

 could be observed when an electric discharge was sent through 

 a vacuum tube connected to the pump ; no difficulty was found 

 in obtaining the helium spectrum when only a tenth as much 

 pitchblende, monazite sand, or thorianite* was used. 



The quantity of gas which was obtained from this amount of 

 carnotite was so small that it was thought worth while to work 

 with a larger quantity of the mineral. For this purpose, 300 

 grams of carnotite of activity 0*8 times metallic uranium was 

 heated at a red heat in vacuo for three hours, and after absorb- 

 ing the carbon dioxide by caustic potash, about 10 cc of a gas 

 remained. On sparking this, after adding oxygen, in order to 

 absorb the nitrogen present, a rapid decrease in volume took 

 place, and when finally the excess of oxygen was absorbed by 

 means of phosphorus, only about 0-l cc of a gas remained. 

 This when introduced into a spectrum tube showed the char- 

 acteristic red spectrum of argon. It was observed that the 

 greater part of the gas, aside from the carbon dioxide, was 

 given off on the first gentle heating, and it is therefore prob- 

 able that the argon was associated with the air held in the 

 powdered mineral, which was completely driven off only on 

 heating it. 



It therefore appears that if helium is contained in carnotite 

 at all, it exists in far smaller amount than would be expected 

 from the quantity of radium present. But it is probable that 



* The recently discovered mineral from Ceylon, containing about 75 per cent 

 of thorium, kindly supplied by Dr. George F. Kunz for this purpose. 



