164 Proceedings of the Royal Society of Edinburgh. [Sess. 
The volume of the charcoal was known from its density and weight after 
complete evacuation. 
The complete evacuation of the charcoal bulb took six days. The initial 
evacuation was accomplished by the water pump, the final by the mercury 
pump when the bulb was immersed in a bath of the vapour of boiling- 
sulphur. At the end the last traces of adsorbed gas were removed by 
means of the second evacuated charcoal bulb immersed in liquid air. The 
evacuation was a very tedious process. The condition of the charcoal in 
Fig 2 
a state of fine powder added to the difficulty, as it was borne upwards by 
the air leaving it. To prevent it going through all the tubes and connec- 
tions a tiny plug of cotton-wool was placed in the head of the ground-glass 
join. The fine powder occasionally stuck in the capillary tube, and had to be 
brought back to the bulb by repeated tapping, or even, after disconnection 
at the join, by vigorous knocking on the bench. Though the volume of the 
bulb was 17 c.cm., it was “filled ” by 4‘5 gm. charcoal (density T63). 
Sulphur dioxide to be adsorbed was kept in the bulb /, immersed in a 
freezing mixture of alcohol and carbon dioxide snow. When freshly made 
up this mixture froze the sulphur dioxide. The air was removed by 
freezing the dioxide in liquid air and evacuating the bulb, the solubility 
of the gas evolved being then 99'99 per cent. When the gas was required 
