OF GASES UNDEE THE BECQUEEEL BAYS. 
513 
I shall now mention the methods of preparation of the gases emj)loyed. It would 
not have been worth while, in view of the limited accuracy of the electrometer 
measurements, to have taken more than ordinary care to secure purity. 
The gases were in all cases dried by passing them slowly over phosphorus j^ent- 
oxide. 
The hydrogen was prepared from sulphuric acid and zinc, and purified by occlusion 
in palladium foil, from which it was subsequently expelled by heat. 
The oxygen was obtained by heating potassium permanganate. 
The hydrochloric acid was made by the action of joure sulphuric acid on rock 
salt. 
The cyanogen was obtained by heating mercury cyanide. 
The carbon dioxide by the action of pure hydrochloric acid on white marble. 
The sulphur dioxide from the liquefied gas commercially supplied, in a “ syphon.” 
The chloroform, methyl iodide, and carbon tetrctcldoride vapours were from the pure 
liquids commercially procured. 
§ 4. Exp)erimerits on the Penetrating Radiation from the Active Barium 
Compound. 
The vessel used to contain the gas was that with the thin copper l^ottom, 
•007 centim. thick, through wliich tlie radiation had to pass. As any easily absorb¬ 
able radiation had already been filtered out by the copper bottom of the vessel, it was 
not to be expected that the rate of leak would be otherwise than simply proportional 
to the pressure; but it was thought best to test this experimentally, partly as a 
guarantee of the accuracy of the method of measurement. 
The following measuremeiits were obtained :— 
Pressure of air, 
millims. of mercury. 
Time taken for 
electrometer needle to 
pass over 50 scale 
divisions. 
Current 
(arbitrary scale). 
735 
seconds. 
17-7 
565 
591 
22-6 
443 
454 
29-4 
340 
.306 
44-6 
224 
136 
95-6 
105 
The measurements of the rate of leak were in each case the mean of about six 
ohsei'vations. The results are plotted on diagranr No. 1, and it will be seen that the 
rate of leak is closely proj^ortional to the pressure up to atmospheric pressure, as was 
anticipated. It was safe, then, to employ any j^ressure within that range. 
VOL. cxcvi. —A. 3 u 
