158 Moss—On the State in which Helium Exists in Pitchblende. 
cavities. It is well known that many minerals contain vast numbers of minute 
cavities. Zirkel estimates that there are as many as 360,000,000 cavities in a 
cubic millimeter of Hiaiinite from Melfi. It is evident that if such minute cavities 
contain gas, even at high pressure,.the quantity of gas that would be liberated 
by grinding the mineral to a fine powder would necessarily be small; the most 
minute sub-division that can be effected by mechanical means would have the 
effect of opening a comparatively small proportion of the cavities. 
Assuming that the helium is contained in pitchblende in such cavities, the 
question arises whether any notable quantity of the gas escapes from the mineral 
at ordinary temperatures. ‘To throw some light upon this point, I enclosed 14 
grammes of the powdered mineral in a tube, along with some fragments of caustic 
potash, separated from the pitchblende by glass wool. In a prolongation of 
the tube there was some phosphorus pentoxide, and attached to this prolongation 
was a branch leading on one side to a Pliicker tube with magnesium terminals, and 
on the other side to a Sprengel pump. The tube was now exhausted until it 
showed the usual green phosphorescence. The Pliicker tube containing the pitch- 
blende was jacketed with water which was slowly brought to the boiling point. The 
discharge was now of a bluish-violet colour. Its spectrum showed the hydrogen lines 
6562 and 4341, but the most prominent lines were those of mercury. I may observe 
that a few globules of mercury had been accidentally mixed with the pitchblende. 
The tubes were now exhausted until the discharge passed with difficulty. Next 
day the mercury lines were again prominent in the spectrum, but there was also 
a faint banded spectrum of nitrogen. On continuing the current, the mercury and 
nitrogen spectrum faded, and the yellow, green, and blue lines of helium became 
faintly visible; but in a short time the resistance of the tube increased, and the 
green phosphorescence made its appearance. I continued to observe the spectrum 
of the discharge from time to time for nineteen days. Every day the helium lines 
became more prominent, and finally no other spectrum except that of mercury 
accompanied the helium spectrum. On the twentieth day I pumped off the 
helium until the tube ceased to conduct. A small bubble, measuring 0:022 c.c., 
was obtained. Hach gramme of the mineral had yielded in nineteen days 0:00016 
c.c. This is less than one-tenth of the quantity obtained in a few minutes by 
pulverizing the mineral 7 vacuo. It is evident that if any gas diffuses from the 
mineral at the ordinary temperature and pressure, the quantity must be very 
small. 
Another specimen purchased as pitchblende from Joachimsthal was broken into 
fragments of about 2 grammes each, and picked as free as possible from matrix ; its 
specific gravity at 15°°5 C. was 6°83. The fragments, weighing 225 grammes, were 
placed in a desiccator over sulphuric acid, and kept there for twelve days. At the 
