18%.] Helium and the associated Gases exist in Minerals. 219 



given off. From 130° to 140° gas was obtained which for the first 

 time showed the D 3 line, indicating the presence of helium. About 

 nine-tenths of this was, however, absorbed by potash. At 160°, 

 200°, and 235° additional but smaller supplies of gas were obtained, 

 consisting of carbon dioxide with about one-fourth of its volume of 

 gas rich in helium. At higher temperatures, up to 446°, smaller 

 volumes of the same mixture were extracted, a definite and limited 

 amount of gas being evolved at each point. 



Cleveite behaved in a similar manner. A single well-formed crystal 

 was used, having only a small flake of mica attached to one side. The 

 whole weighed 3'7 grams. Gas was first evolved rather suddenly at 

 110°, and at successive intervals of about 25° it gave off successive 

 portions of gas containing helium. 



In order to ascertain if the mineral from which the gas had been 

 removed was capable of re-absorbing it, some massive Swedish 

 cleveite was powdered and divided about equally between two bulbs, 

 A and B, sealed to a small tube filled with soda-lime, and attached to 

 the Sprengel pump. Both bulbs were first heated to 100° and 

 exhausted ; A was then heated to 160°, and the gas completely 

 pumped out. The bulbs were then shut off from the pump by a tap, 

 aud B was heated to low redness so as to generate gas within the 

 apparatus. This gas, from which carbon dioxide was absorbed by 

 the soda-lime, was left in contact with the mineral in A for about 

 nine weeks at summer temperature. On heating A by an oil bath 

 and working the pump no gas could be collected below 160°, the 

 temperature to which the mineral had been previously heated. This 

 result seemed to show that cleveite does not re-absorb the helium mix- 

 ture at the pressure employed in this experiment, which was prob- 

 ably somewhat less than one atmosphere. The pressure could only 

 be guessed at in this form of experiment from observation of the 

 capacity of the apparatus and the amount of gas given off by the 

 same mineral when heated to redness. 



9 5 grams or 1'8 c.c. of this sample of cleveite gave at a red heat 

 15'6 c.c. of crude gas, which after contact with potash was reduced 

 to 6'3 c.c. The mineral therefore gives 3"5 times its volume of gas 

 free from carbon dioxide. 



A second experiment, conducted on a similar principle, but with a 

 greater pressure of gas, gave a different result. Two bulbs were used 

 as before, but while 10 grams were placed in A as the absorbent, 

 40 grams were used in B as the generator. B was heated by means 

 of an air bath to about 400°, and a mercury-air gauge attached 

 then showed a pressure of about 2| atmospheres. A was first heated 

 to 165° and the gas removed, and the gas having been generated in 

 B, A was heated to 100° and cooled several times in contact with 

 the gas. The bulb A was then cut off, sealed on to the Sprengel 



H 2 



