=Digesters.=--The “digester” indicated, together with its method of suspension and nesting has been successfully used and was the practice followed by a well known designer for a number of years. The diameter and height of the digester ordinarily used is 6 × 16 feet on the tank body. The writer invariably has specified half-inch thick tank steel for the reason that the increased thickness is of so little additional weight, and the labor being such a considerable factor, that it was thought well to provide this additional thickness to take care of corrosion and acid attack. =Little Neck Rendering Tank.=--Lugs can be placed in any position desirable for support. The little neck for filling needs no comment. It is provided with a six-point security and by the use of ring-bolts with male and female flanged closing and gasket, can readily be made steam tight. =Tank Gate Valve.=--Tank department foremen are divided in ideas as to using sliding steam gate valves, in which the gate is operated by lever for quick opening or the screw type valve. The latter should be the rising stem type. =Surface Box.=--The surface box shown is a jacketed type used for plants where tank water is collected for evaporation. The cost of this is justified as against being annoyed with coils in the tank. =Press and Pump.=--Practically all presses now in use are hydraulic. These are overhead or under types, the latter being mostly used. [Illustration: FIG. 68.--SECTION OF RENDERING TANK.] [Illustration: FIG. 69.--DESIGN OF STEAM JACKETED SURFACE BOX.] The style of pump used is a question of importance. The writer specifies steam operated hydraulic pumps in preference to power driven pumps, since the former can be operated from a governor that automatically keeps full pressure on the pump. With the power pump, when the motive power is stopped, a leak, the size of a pin point, in a valve, will cause a leakage that releases the pressure and makes poor pressing. Be aware of the fact that there is no method of extracting water from the fertilizer so cheap as pressing and the only limit should be the strength of the cloths. Fig. 70 shows how a hydraulic press and pump should be connected. [Illustration: FIG. 70.--DIAGRAM OF HYDRAULIC PRESS WITH PIPING AND PUMP.]