DRYING BOX OR CUPBOARD (Pr., Etuve, Armoire ; Ger., Trockenofen) A light-tight box or cupboard used in drying gelatine plates after coating, and for othcr photo graphic purposes. The chief requirement is the circulation of a current of dry air, in order that the internal air may be continuously drawn away, carrying with it by degrees the moisture from the plates. The temperature of the drying cupboard requires to be raised, but perfect ventilation is of greater importance. A pattern recommended by W. K. Burton consists of a box with a closely fitting light-tight door, and having light-trapped air openings at top and bottom. Beginning near the bottom, a bent channel or flue runs up against one side of the box, a gas burner being inserted in it near the top. When the burner is lit it draws a current of air through the flue from below, and consequently ensures a con stant circulation of air in the box. Another kind of drying cupboard is warmed from beneath by a gas-ring or oil stove, a sheet-iron bottom being fitted. Light-trapped openings at the lower portion of the sides and a cowled ventilator at top furnish the necessary air current.
In process work, the arrangement for drying collotype plates is usually in the form of a box or trunk supported about 12 in. from the floor on four legs. The bottom consists of an inverted sheet-iron box, under which is placed a gas-ring or pipes. Holes are punched in the side of the box to prevent the gas becoming choked. The wooden part of the box is about 18 in. deep. About 6 in. from the top are two iron bars, resting on ledges at the sides of the box. These bars are provided with screws placed at suitable distances with their points upwards. The plates rest on these screws, and
by adjustment of the latter can be levelled up, so that the gelatine solution on the plates will not run off. The bottom of the box is usually covered with sand to equalise the heat. The lid of the box is covered with gauze or an open textured cloth, so that the moist air can pass through. A thermometer is inserted into the box through a hole in the lid.
Process workers find a drying cupboard necessary for quite a number of purposes; in one convenient form the bottom takes the form of an inverted sheet-iron box, and there are holes in the sides to allow the gas fumes to escape, or a flue pipe can be led out from the back. In the sides of the wooden part, just above the sheet-iron bottom, are holes for drawing in a current of air ; these holes are covered with a baffle-board sloping towards the bottom. Shelves or racks can be placed in the cupboard. On the top a metal cowl ventilator is placed. For heating, an ordinary gas-ring burner is placed underneath the bottom. The cupboard can be elaborated by placing an electric radiator inside and an electric fan on top to draw out the air. The incoming-air can also be made to pass through an opening packed with damp cotton wool, so as to stop any dust entering. For colour-sensitising dry plates the cupboard must, of course, be made perfectly light-tight. Such a cupboard is very convenient for drying photo lithographic paper and carbon tissue, and will be found generally useful.