FIG. 70.—DIAGRAM OF HYDRAULIC PRESS WITH PIPING AND PUMP.
Cooking Killing Stock.
—The tank should be clean; draw in about two hogsheads of water for a 6 × 16 foot tank, or a proportionate amount for tanks of other sizes; turn on the steam to boil the water, and then begin filling the tank. Allow sufficient steam to enter to keep the tank boiling slowly. When the tank is two-thirds full, shut off the steam, draw off the water and refill with water; turn on the steam, bringing the contents to a boil the second time. Do not fill the tank to exceed three-fourths full, as the cooking is better done if sufficient room is left. After cooking for a half hour, draw off the water a second time. It will be found, especially in cooking product from the killing department, that the water drawn off is dark colored, from the blood and dirt that has accumulated on the tissue. If this is not withdrawn it has the effect of darkening the lard or tallow materially.
After the water has been drawn the second time, put on the tank head and turn on the steam, the condensation from the steam is sufficient to cook the material; no more water is needed. See that the blow-off and escape pipes are shut and the pet-cock is open. Continue cooking in this manner until a moderate pressure is built up, then admit steam to full pressure of forty-five pounds, open the escape valve just enough so that you may know the gas is escaping. At the completion of this operation the cooking begins. A tank of tallow should cook thoroughly in from nine to ten hours with forty pounds pressure.
Cold Spots.
—Oftentimes freshly killed material will lie closely together and a “cold spot” will occur—a spot where the material has become partially solidified and the steam has not penetrated. In such case, shut off the steam, draw off the water, and then turn on the steam, the cold spots will disappear. “Cold spot” has the effect of souring lard and tallow; in other words before the heat has penetrated into the solid mass, the heat surrounding it will have caused it to sour. This point should be watched closely, especially in cooking lard.
Tankmen should try the pet-cock on the tank each half hour to find out if the tank is “flush.” If the tank is “flush” or foaming, the foam will come out instead of steam. In this case, shut off the tank ten minutes, then draw off the water, but see that no grease is drawn off with it. The cause of the flushing, or foaming, is that the tank is too full, or that there is too much water in it, consequently it is necessary that the tankman should try his pet-cock very often during the operation of cooking to see that the contents are being properly cooked.
Cutting Tanks.
—Cuttings and cold products of like character are usually carried in cold water while filling, and are not parboiled as described for “killing” tanks.