train of clockwork, sometimes from a separate supply of water under high pressure. The clockwork or the water power is used either to drive a piston travelling through the vessel containing the carbide so that the proper quantity of material is dropped over the open mouth of a shoot, or to upset one after another a series of carbide receptacles, or to perform some analogous operation. In these cases the pin or other device fitted to the acetylene apparatus itself has nothing to do beyond releasing the mechanism in question, and therefore the work required from the bell is but small. The propriety of employing a generator belonging to these latter types must depend upon local conditions, _e.g._, whether the owner of the installation has hydraulic power on a small scale (a constant supply of water under sufficient pressure) at disposal, or whether he does not object to the extra labour involved in the periodical winding up of a train of clockwork. It must be clear that all these carbide-feed arrangements have the defect in a more or less serious degree of leaving the carbide in the main storage vessel exposed to the attack of water vapour rising from the decomposing chamber, for none of the valves or operating mechanism can be made quite air-tight. Evolution of gas produced in this way does not matter in the least, because it is easy to return the gas so liberated into the generator or into the holder; while the extent of the action, and the consequent production of overheating, will tend to be less than in generators such as those shown in G and H of Figs. 4 and 5, inasmuch as the large excess of water in the carbide-feed apparatus prevents the liquid arriving at a temperature at which it volatilises rapidly. The main objection to the evolution of gas in the carbide vessel of a carbide-to-water generator depends on the danger that the smooth working of the feed-gear may be interfered with by the formation of dust or by the aggregation of the carbide lumps.