ACTION OF WATER-TO-CARBIDE GENERATORS.--Having by one or other of the means described obtained a supply of water intermittent in character, it remains to be considered how that supply may be made to approach the carbide in the generator. Actual acetylene apparatus are so various in kind, and merge from one type to another by such small differences, that it is somewhat difficult to classify them in a simple and intelligible fashion. However, it may be said that water-to-carbide generators, _i.e._, such as employ water as the moving material, may be divided into four categories: (F^1) water is allowed to fall as single drops or as a fine stream upon a mass of carbide--this being the "drip" generator; (F^2) a mass of water is made to rise round and then recede from a stationary vessel containing carbide--this being essentially identical in all respects save the mechanical one with the "dip" or "dipping" generator shown in A^2, Fig. 1; (F^3) a supply of water is permitted to rise round, or to flow upon, a stationary mass of carbide without ever receding from the position it has once assumed--this being the "contact" generator; and (F^4) a supply of water is admitted to a subdivided charge of carbide in such proportion that each quantity admitted is in chemical excess of the carbide it attacks. With the exception of F^2, which has already been illustrated as A^2 Fig. 1, or as B^1 in Fig. 2, these methods of decomposing carbide are represented in Figs. 4 and 5. It will be observed that whereas in both F^1 and F^3 the liberated acetylene passes off at the top of the apparatus, or rather from the top of the non-subdivided charge of carbide, in F^1 the water enters at the top, and in F^3 it enters at the bottom. Thus it happens that the mixture of acetylene and steam, which is produced at the spot where the primary chemical reaction is taking place, has to travel through the entire mass of carbide present in a generator belonging to type F^3, while in F^1 the damp gas flows directly to the exit pipe without having to penetrate the lumps of solid. Both F^1 and F^3 exhibit after-generation caused by a reaction between the liquid water mechanically clinging to the mass of spent lime and the excess of carbide to an approximately equal extent; but for the reason just mentioned, after-generation due to a reaction between the vaporised water accompanying the acetylene first evolved and the excess of carbide is more noticeable in F^3 than in F^1; and it is precisely this latter description of after-generation which leads to overheating of the most ungovernable kind. Naturally both F^1 and F^3 can be fitted with water jackets, as is indicated by the dotted lines in the second sketch; but unless the generating chamber in quite small and the evolution of gas quite slow, the cooling action of the jacket will not prove sufficient. As the water in F^1 and F^3 is not capable of backward motion, the decomposing chambers cannot be employed as displacement