the carbide impurities from acetylene, so far as that removal is desirable or necessary; it should not be called upon to extract the generator impurities, because the proper way of dealing with them is, to the utmost possible extent, to prevent their formation. The sole exception to this rule is that of water-vapour, which invariably accompanies the best acetylene, and must be partially removed as soon as convenient. Vapour of water almost always accompanies acetylene from the generator, even when the apparatus does not belong to those systems of working where liquid water is in excess, this being due to the fact that in a generator where the carbide is in excess the temperature tends to rise until part of the water is vapourised and carried out of the decomposing chamber before it has an opportunity of reacting with the excess of carbide. The issuing gas is therefore more or less hot, and it usually comes from the generating chamber saturated with vapour, the quantity needed so to saturate it rising as the temperature of the gas increases. Practically speaking, there is little objection to the presence of water-vapour in acetylene beyond the fear of deposition of liquid in the pipes, which may accumulate till they are partially or completely choked, and may even freeze and burst them in very severe weather. Where the chemical purifiers, too, contain a solid material which accidentally or intentionally acts as a drier by removing moisture from the acetylene, it is a waste of such comparatively expensive material to allow gas to enter the purifier wetter than need be.