A PHOTOGRAPHIC PA PER FACTORY.
Fig. 30S shows the actual plan used in the construction of one of the largest photo graphic factories in the world. It consists of a large building divided into two parts, both of which, although not absolutely dark, are illuminated only by a minimum of non-actinic light, so little as to leave not the slightest chance of fog during the brief period of exposure. As manufacture paper in ten hours. Several exhaust air ducts may be provided, as shown in end elevation at u, Fig. 310. Slight modifica tions exist in certain cases arising from local conditions ; but this description is sufficient to make the general principle understood.
under the latest conditions goes on almost automatically, the room may remain in complete darkness, except when it is ne cessary to ascertain that things are pro ceeding satisfactorily. The small room is the actual coating room, and contains the coating machine ; the large room in which the paper is dried and reeled is divided into compartments, so that the temperature of the different parts may be under separate control. This division into compartments is absolutely necessary, for were it attempted to dry the paper straight away in warm air, it would simply melt and run. Cold air is first of all pumped in at A, by means of a motor B, after passing through a refrigerator. By this means, the emulsion is well set on the surface before reaching the hot-air cham ber. The hot air passes into this room, as shown, at the air intake, and through a suitable heating apparatus ; so that a stream of perfectly dry hot air is blown in at c, through a filter of cotton-wool to exclude all dust, and passed along pipes at D. Connecting these two pipes, per forated cross pipes are fixed at intervals, through which the hot air escapes up wards. and finds its way out through the
exhaust air duct, which is controlled by a second fan at c (see elevation. Fig. 309). In this way it is possible to dry 9,000 ft. of How THE PAPER IS COATED The method by which the paper is covered by a thin film of emulsion and rapidly carried away into the drying room will now be described. Fig. 311 represents the machine employed for this purpose. Very fine hard paper, coated with baryta, is used. The paper is placed upon a spool or reel at A, whence it passes under two small wheels (not shown), which put a slight drag upon the paper and keep it taut and even. It next passes between the two rollers B and c, up to the aperture in the coating room. The roller B is of nickel silver, and revolves in a silver pan, which rests in a hot-water jacket, kept so supplied that the emulsion always remains at the same temperature. The roller c is filled with ice-water. The emulsion is poured into the pan, and the roller B volves through it, picking up a certain raising or lowering can be made to give a coating of any desired thickness. As the coating is applied, it is instantaneously set quantity on its surface and depositing it on the surface of the paper above as it passes along. The roller can be regulated by means of the ice-water cylinder c, which is just a little longer each way than the roller B. The latter does not quite cover with extreme nicety, so that it just brushes off the emulsion on to the paper, and by the entire width of the paper ; thus leaving a " safe-edge " on each side for the wheels n n, which keep the paper firmly in posi tion.