=Tank House Design.=--Almost any arrangement of tank, surface box and press can be made to serve the purpose of rendering. The method and arrangement shown herein are those practiced by one of the revisors of this work and embodies principles as described. The requisite apparatus for a rendering or tank house consists of but few articles, viz: the rendering tank or digester, the surface or skimming box, and a press, but the design and operation is of such consequence that the same will be described in detail. =Isolation and Ventilation.=--The rendering building from its character should be isolated and arranged for ventilation on at least three sides. The United States sanitary requirements compel the complete separation of the edible from the inedible section by the use of separate buildings or a parting wall. [Illustration: FIG. 65.--SECTION THROUGH TANK HOUSE.] =Separation of Press Room.=--If the business is large the owner is fully justified in extending the parting wall through and dividing the press room. This arrangement requires the double investment in presses, cloths and all equipment, but gives the advantage that the pressings can be collected from edible tankage and used for edible purposes, provided always that the equipment is kept in proper shape. Whereas, if the parting wall is not extended through the press room, the oils are considered contaminated and are usable only for inedible purposes. [Illustration: FIG. 66.--LITTLE NECK RENDERING TANK.] The section shown indicates that type of house where the press room is single, and the house above the press floor is divided. [Illustration: FIG. 67.--TANK HOUSE, SHOWING NESTING OF TANKS.] =Tank House Hazards.=--The tank house, from the nature of the business being hazardous, is best to be of fire-proof construction. Tanks constructed as shown in Fig. 66, with the little neck head can be nested four in a bay and be made fully accessible on all floors. The nesting of tanks six feet in diameter in a sixteen-foot square bay provides sufficient strength to make it possible to suspend the tanks from the floor beams above, suitably arranged, it further avoids the necessity of supports near to the tanks, which greatly facilitate cleanliness. =Situation of Surface Boxes.=--The grease content in the fertilizer is a matter of dollars and cents. When the oil is withdrawn from the tanks it cannot be seen and no matter how closely watched considerable oil will pass through to the surface box where it can be collected. Consequently the second story of the tank house is a high story with the surface boxes placed convenient to the second floor so as to be readily worked. Further reference to this is made later. =Press Room.=--The press room is arranged so that the press can be built directly beneath the surface boxes, from whence the car is passed to the press for pressing out the moisture.