220 Dr. W. A. Tilclen. On the Condition in which [Jan. 23, 



Fjg. 1. 



pump, and exhausted completely at air temperature. Heated to 100° 

 it gave only a tiny bubble of gas, but at 115° evolution of gas com- 

 menced, and continued till the temperature of 150° was reached. The 

 interval of about 20°, between this and the temperature at which the 

 mineral was originally extracted, seemed sufficient to prevent sus- 

 picion that the gas now obtained was due to the natural charge, and 

 had not been re-absorbed. The gas contained hydrogen, helium, and 

 nitrogen, and amounted to about 1/25 of the volume of the mineral. 

 After cooling to the air temperature the bulb was a second time 

 heated to 150°, but no further evolution of gas occurred. The same 

 cleveite in its natural state gives, when heated to 170°, about one- 

 third of its volume of the helium mixture. 



An experiment was now made with a portion of the mineral which 

 had been used to generate the gas in the preceding experiment, and 

 it was found that in contact with the gas at a pressure between 2 and 

 3 atmospheres an amount was taken up about equal (1/24 volume) to 

 that which was absorbed by the mineral which had been heated only 

 to 170°, but while the gas thus removable below the temperature of 

 150° contained helium, it also contained carbon dioxide, which seemed 

 to suggest that helium or one of the other gases by which it is accom- 

 panied is capable of displacing carbon dioxide from cleveite. 



In order to test the effect of greater pressures it was necessary to 



