THE COMBINING VOLUMES OF HYDROGEN AND OXYGEN. 
395 
gases through the taps, G and H, to the drying trains. Before one of the manometers 
was sealed on, a hot saturated solution of Kahlbaum’s barium hydroxide, which had 
been four times re-crystallised by us, was filtered through glass wool into the U-tube ; 
the manometer was immediately sealed on, and electrolysis started, and then the 
vessel was exhausted by a water pump until the solution boiled. Finally, both 
hydrogen and oxygen were allowed to run to waste through the gauges for a 
considerable time, so as to complete the elimination of air. A large proportion of 
the hydroxide crystallised out on cooling, and partially dissolved again when the 
temperature rose owing to passage of the current. No partition or diaphragm was 
employed in the U-tube, as the subsequent treatment of both hydrogen and oxygen 
was designed to remove traces of the other gas. A current of about 1'5 amperes was 
used for electrolysis, and the solution was not allowed to get very hot. 
Purification of Hydrogen : First Method. 
The hydrogen from the electrolysis vessel, after passing through two drying tubes 
filled with calcium chloride, J, J, and two filled with Merck’s phosphoric oxide, K, K, 
entered the 2^-litre storage bulb, L, which was fitted with a 3-way tap. This bulb, after 
exhaustion by a water pump and a mercury pump, had had the last ti’aces of air 
3 h 2 
