of the tank is a sheet of plate glass bedded on a
sand bath. An assistant at one end places the glasses one after the
other on the warm glass slab, and by means of a movable slide pushes
them one at a time under the cover, which cover is represented raised
in the engraving to show the interior of the machine. After having put
one glass plate on the slide, another cannot be added until the man in
the dark room at the other end of the slide has taken off the farthest
warmed plate, because the slide has a reciprocating movement. This
heating apparatus is built at right angles to the coating machine in
the next room, in order to be conveniently placed in the present
building; but it is intended in future to use it as a part of the
coating machine itself, and to drive it at the same speed and with the
same gearing, so that the cold plates will be put on by hand at one
end, get warmed as they pass into the dark room, at the other end of
which they will be delivered by the machine in coated condition.
Underneath the heating table is a copper boiler, with its Bunsen's
burner of three concentric rings to get up the temperature quickly and
to give the power of keeping the water under the heating slab at a
definite temperature, as indicated by a thermometer. The cold water
tank of the system is represented against the wall in the cut.

[Illustration: Fig. 6.]

Fig. 5 represents the hot water circulating system outside the coating
rooms for keeping the gelatine emulsions in these dimly lighted
regions at a given temperature, without liberating the products of
combustion where the emulsion is manipulated. The temperature is
regulated automatically. It will be noticed where the pipes enter the
two coating rooms, and Fig. 6 shows the copper inside one of them
heated by the apparatus just described. The emulsion vessel in the
copper is surrounded by warm water, and the copper itself is jacketed
and connected with the hot water pipes, so forming part of the
circulating system.

[Illustration: Fig. 7.]

Fig. 7 is a general view of the coating machine recently invented by
Mr. Cadett, of the Greville Works, Ashtead, Surrey. The plates warmed
in the light room, as already described, are delivered near the end of
the coating table, where they are picked off a gridiron-like platform,
represented on the right hand side of the cut, and are placed by an
assistant one by one upon the parallel gauges shown at the beginning
of the machine prop