DRYING MACHINERY. Drying ma chines and processes have become very com mon ih the industries. Time is always a valuable clement in every factory, and artificial dryers supply methods of hastening production. One of the simpler methods of drying is by gravity, as practised in the recovery of metals from slimes, by settling tanks and vacuum filters. Absorption by temporary mixture or contact with a dry, absorbent substance, as sawdust, is accomplished on the blotting paper principle in some trades. The chemist often employs a desiccating substance, as quicklime, placing it in the same vessel, below the sub stance which is to be dried; large clay articles, as toilet fixtures, are dried on this principle. Condensation by refrigeration is another drying process, illustrated in Gayley's air-drying ap paratus for blast furnaces. (See BLAST FUR NACE ) . A familiar form of dryer is termed the hydro-extractor or centrifugal machine. A wet substance, as laundry, is rotated in a basket at high speed, and the water thrown out by centri fugal force. Many sorts of drying mechanisms depend on natural evaporation, mechanically assisted. The atmosphere is capable of taking up moisture to the point of saturation. The more dry air can be placed in contact with a thing in a given time, the quicker will it take up the moisture so that it disappears. Therefore blowers and exhaust fans are utilized to dry wet and moist goods in a great number of manufacturing operations, on the same prin ciple that the old-time washerwoman hung her clothes on a line in the wind. Another method is to move the goods through the air, and con veyor dryers are especially economical when the goods have to be transported to another part of a factory for a following operation.
Pressure is in many cases a satisfactory means of drying. It is used in garbage utilization works to expel the moisture, as for making a fertilizer from kitchen refuse.
The application of heat is of course the most natural process of drying, and is made use of in countless ways. The steelmaker heats air in great checkered stoves to assist the operations of the blast furnace with a hot blast; boilers, radiators, stoves and heaters of practically end less forms are used in the majority of trades for drying purposes. Kilns and roasting fur naces are made with rotating cylinders through which material is passed until the last vestige of moisture is removed. Hot ovens and long heated tunnels are other devices for the same purpose. In both brickmaking and soap manu facture the hot tunnel is serviceable. The papermaker runs the continuous strip of paper from the fourdriner machine 'between hot calendar rolls to dry thoroughly his product in a few seconds. The lumber dealer is satisfied with storing his lumber in specially constructed buildings where the drying up of the sap can be accomplished in a few weeks or months. Manufacturers of cotton and woolen cloths, bleachers, dryers and practically all handlers of textiles have to resort to dryers to hasten their production. The printer has to put dryer in his inks, and keep his pressroom hot and his paper dry. The brickmaker, cement manufacturer, tiletnaker, etc., all depend on kilns of some sort to rid their material of moisture. It would re quire a complete encyclopaedic account of all the manufacturing processes in use to exhaust the details of methods and mechanisms for drying.