156 Moss—On the Stale in which Helium Exists in Pitehblende. 
[ next proceeded to ascertain the quantity of helium and carbon dioxide in 
this powder by decomposing it chemically. For this purpose 25 grammes of the 
powder was mixed with 65 grammes of hydrogen potassium sulphate. The 
mixture was placed in a capacious glass tube, which was attached by a mercury- 
jacketed rubber jomt to a combustion tube 50 cm. in length and 1°5 em. 
diameter, containing granulated copper oxide which had been heated to redness, 
and cooled in an atmosphere of oxygen. This tube was attached by anothey 
mercury-jacketed rubber joint to a tube 25 em. long, and 7 mm. in diameter, 
packed with phosphorus pentoxide, and leading to the Tépler pump. The copper 
oxide was heated to low redness, and the tubes were thoroughly exhausted. The 
next day, having ascertained that no leakage had taken place, the copper oxide 
was heated to redness, and the hydrogen potassium sulphate was fused, and kept 
in that state for three hours. The pump was kept working during the whole 
operation, and while the fused mixture was cooling. The gases evolved were 
collected in four lots. ‘These were free from sulphur dioxide, except the last lot, 
which contained some of that gas which was removed by moist manganese dioxide. 
The total volume of gas thus obtained was 73°797 c.c. (reduced to 0°C. and 760 
mm. pressure). 
On absorbing carbon dioxide, the volume was reduced to 4:911 ¢.c.; alkaline 
pyrogalol caused a further contraction to 4:°799 cc. This gas was now mixed 
with an equal volume of pure oxygen, and sparked in an eudiometer; there was 
no alteration in volume, as might be expected, nor was carbon dioxide produced. 
The volume was now made up to about 26 ¢.c. by the further addition of pure 
oxygen, and the mixture was sparked in the usual way over a solution of caustic 
alkali for three hours, when contraction seemed to have ceased. ‘To ensure as 
complete a removal of nitrogen as possible, the sparking was continued for two 
hours more. On removing the excess of oxygen by combustion with phosphorus, 
the residual gas was found to measure 1°596 ¢.c. ‘This was introduced into a 
Pliicker tube with magnesium terminals, and with a phosphorus pentoxide tube 
attached. ‘hese tubes had been previously exhausted until the Pliicker tube 
showed green phosphorescence, and the current passed with difficulty. Notwith- 
standing the long-continued sparking with oxygen over alkali, the spectrum at first 
observed was that of nitrogen, with the green line of mercury prominent. On 
introducing a Leyden jar and spark-gap into the secondary circuit, and passing 
the current for a few minutes, the nitrogen was absorbed, and the spectrum 
now obtained showed only the helium and mercury lines. By circulating the gas 
through the Pliicker, tube as already described, while the current was passing, 
the nitrogen was removed from the gas in all parts of the apparatus. ‘The gas, 
now consisting of helium alone, was pumped off and found to measure 1-560 c.c. 
