133 
means of a short length of pressure tubing, a T piece of glass 
tubing with two stopcocks was connected to the mouth of the 
bottle. The unstoppered leg of the T-piece to the side was closed 
by a short length of rubber tubing with a glass stopper. The up- 
per part of the T tube was graduated to tenths of a c.c. The 
side tube of the bottle was connected to a two bulb reduction 
tube to act as a balance. The mineral being placed in the bottle 
with a little water, it was heated to boiling to expel any air 
within the pores of it. The apparatus was then fitted together 
and filled completely with cold recently-boiled acid, the top stop- 
cock closed and the bottle placed on the water bath for several 
hours. The helium was determined in both un crushed and finely 
crushed mineral. Since Moss * has shown that helium escapes 
on grinding a radio-active mineral and since the generally accepted 
theory is that helium is only mechanically imprisoned in the 
mineral, f it was to be expected that more helium would be ob- 
tained from the uncrushed than from the crushed mineral. The 
actual results obtained were — 
Mineral taken gms. 2.5 2.5 2.5 2.5 
Condition Crushed Crushed Uncrushed Uncrushed 
scraped unscraped 
Acid 5E HC1 5E H 2 S 0 4 5E HC 1 5E HC 1 
Helium, c.c. at N.T.P. 0.55 0.65 0.96 0.97 
Helium per gin. of mi- 
neral 0.22 0.26 0.38 0.39 
Sulphuric acid was found to be the best for the liberation of 
helium from the powdered mineral, hydrochloric being so rapid 
in action that the apparatus could not be filled and stoppered 
without loss of gas. In the case of the uncrushed mineral, which 
was in masses of about 0.5 gm. each, sulphuric acid was found 
to be useless, as it failed even after two days to penetrate to the 
centre of the mineral, which became protected by a coating of 
insoluble sulphate of lead and thorium. Hydrochloric acid of 
5E strength on the contrary was found to be conveniently slow 
in action in the cold and very energetic on heating, lead uranium 
and thorium rapidly dissolving and leaving a flocculent mass of 
silica. The greater part of the helium was obtained in this way 
in half an hour, the whole of it at the end of about eight hours. 
By occasionally compressing the short rubber tube on the side 
limb of the T piece the whole of the helium was made to collect 
in the upper graduated part of the apparatus. After replacing 
the acid in the T piece by freshly boiled water the gas was measured 
at atmospheric pressure and its volume reduced to normal tem- 
perature and pressure. 
* Trans. Roy. Soc. of Dublin, 1904. 
f Rutherford, Radioactivity, 2nd Edition, p. 485. 
