Before being cleaned all sharp edges are roughly taken off those plates intended for machine coating by girls, who rub the edges and corners of the plates upon a stone; the plates are then cleaned by any suitable method in use among photographers. The plates, now ready for the coating room, have to be warmed to the temperature of the emulsion, say from 80 deg. F. to 100 deg. F., before they pass to the coating machine, the inventor of which, Mr. Cadett, having come to the conclusion that, if the plates are not of the proper temperature, the coating given will be uneven over various parts of the surface. The plate-warming machine is represented in Fig. 4; it was designed by Mr. A. Cowan, and made by his son, Mr. A. R. Cowan. It consists of a trough 7 ft. long by 3 in. deep, forming a flat tank, through which hot water passes by means of the circulating system shown in the engraving. To facilitate the traveling of the glass plates without friction the top 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.]