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.
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