In operating Pocket kilns, woods of different texture and thickness should be separated and placed in different drying rooms, and each kiln adjusted and operated to accommodate the peculiarities of the species and thickness of the material to be dried. [Illustration: Fig. 37. Exterior View of Five Pocket Dry Kilns, built in Two Batteries with the Front of each Set facing the other, and a Transfer System between. They are also equipped with the asbestos doors.] Naturally, the more complex the conditions of manufacturing wood products in any industry, the more difficult will be the proper drying of same. Pocket kilns, are, therefore, recommended for factories having several different kinds and thicknesses of material to dry in small quantities of each, such as: Planing mills; Chair factories; Furniture factories; Sash and door factories; etc. The "Tower" Dry Kiln The so-called "Tower" dry kiln (see Fig. 38) is designed for the rapid drying of small stuff in quantities. Although the general form of construction and the capacity of the individual bins or drying rooms may vary, the same essential method of operation is common to all. That is, the material itself, such as wooden novelties, loose staves, and heading for tubs, kits, and pails, for box stuff, kindling wood, etc., is dumped directly into the drying rooms from above, or through the roof, in such quantities as effectually to fill the bin, from which it is finally removed when dry, through the doors at the bottom. These dry kilns are usually operated as "Blower" kilns, the heating apparatus is generally located in a separate room or building adjacent to the main structure or drying rooms, and arranged so that the hot air discharged through the inlet duct (see illustration) is thoroughly distributed beneath a lattice floor upon which rests the material to be dried. Through this floor the air passes directly upward, between and around the stock, and finally returns to the fan or heating room. This return air duct is so arranged that by means of dampers, leading from each drying room, the air may be returned in any quantity to the fan room where it is mixed with fresh air and again used. This is one of the main features of economy of the blower system of drying, as by the employment of this return air system, considerable saving may be made in the amount of steam required for drying. [Illustration: Fig. 38. Exterior and Sectional View of a Battery of Tower Dry Kilns. This is a "Blower" or "Hot Blast" type, and shows the arrangement of the fan blower, engine, etc. This type of dry kin is used principally for the seasoning of small, loose material.] The lattice floors in this type of dry kiln are built on an incline, which arrangement materially lessens the cost, and increases the convenience with which the dried stock may be removed from the bins or drying rooms.