398 
DR. F. P. BURT AND DR. E. C. EDGAR ON 
second. The tube prepared from forged sponge showed a marked tendency to become 
crystalline and develop cracks, and for this reason was soon discarded. We have to 
express our indebtedness to Messrs. Johnson and Matthey for the great trouble they 
took in preparing tubes that would satisfy our requirements. 
Before admitting hydrogen it was necessary to make certain that both the palladium 
itself and the glass-platinum junction were perfectly gas-tight. The palladium tube 
was evacuated by means of the mercury pump while the drying train was left full of 
air at atmospheric pressure, and the apparatus was allowed to stand overnight. In 
the morning the mercury gauges at D and E indicated no alteration in pressure on the 
two sides of the system, nor could any gas be obtained from the pump. After the 
palladium tube had been strongly heated, the vacuum still held. The drying train 
was now exhausted at the T-piece, F, and the palladium heated to a much higher 
temperature than was ever afterwards reached in the actual determinations. The 
train was then washed out with hydrogen, and this operation was repeated till all air 
was removed, when the T-piece, F, was sealed off. 
Sometimes difficulty was experienced in “ activating ” the palladium. This could be 
effected by heating in vacuo, by heating in hydrogen, or, perhaps most surely, by 
heating in air. Once activated, the palladium remained in this condition throughout 
our experiments. The superficial film of oxide formed by heating in air disappeared 
when hydrogen was admitted. All the tubes used by us were permeable to hydrogen 
even in the cold, but the rate of passage of the gas was exceedingly slow. No move¬ 
ment of mercury in the gauges could be detected by eye, and equilibrium was only 
established after ten or twelve hours when the initial difference of pressure on the two 
sides of the system was as great as half an atmosphere. 
In order to obtain hydrogen in the requisite quantities, the following procedure was 
adopted :—Electrolysis was continued until the pressure of hydrogen in the palladium 
was nearly atmospheric; if the palladium was heated at once, almost all the gas was 
evolved from the surface at which it had entered ; if twenty-four hours were allowed 
to elapse before heating, hydrogen was evolved freely at both sides of the system. By 
keeping the metal at a temperature of 100 C. during charging, the process of diffusion 
was greatly accelerated. The required quantity of gas was obtained by heating to a 
temperature of 180° C. ; after the expulsion of about 300 c.c., the metal was at once 
recharged at a lower temperature. 
When the palladium was allowed to cool, the mercury in the gauge, E, rose 
rapidly to atmospheric height, and then fell very slowly till its level was the same as 
in the gauge, D. The life of the tube was certainly prolonged by keeping the 
palladium fully charged with hydrogen, and by using only a gentle heat to expel the 
gas. In order to obviate waste of gas through the gauge, D, a 2^-litre storage bulb 
was attached to the train immediately after the electrolysis vessel. The palladium 
was protected from the action of mercury vapour by plugs of fine gold wire at G 
and H. 
