Blood.
—The sources of the collection of blood are from animals slaughtered, viz: cattle, sheep, calves and pigs. In nearly every instance this is collected at a given point near the sticking rails and transferred to the fertilizer department for processing.
It is rather difficult to pump blood, although it can be readily done with a ball valve pump, or a centrifugal pump. The latter is satisfactory if foreign substances can be kept out, and if the reservoir can be situated high enough so that the blood can gravitate to the suction of the pump. Mechanical agitation is a benefit in the receivers. A very satisfactory way to handle blood is by means of a blow tank. This is a tight, heavily constructed cylinder with an admittance valve on the inlet pipe, and a closing valve on the discharge pipe; the latter preferably a quick opening valve. A means for admitting air or steam to the blood is arranged. To operate, the valve on the inlet line as well as the outlet valve is closed, and air or steam pressure is built up as required for the lift. The outlet valve is then quickly opened when the contents of the tank is virtually “shot” to the receiving tanks.
Receiving Tank.
—This is preferably a closed type of tank with an air vent to allow displacement of air when blowing blood. It is preferably situated above the cook tank with an admittance valve between them so that blood can be lowered to the cooking tank at will.
Cooking.
—Blood should be “baked,” not boiled. By this is meant, the steam should be admitted slowly and the heat dispersed through the mass rather than boiled violently, by admitting high pressure steam. The blood, by this method, seems to coagulate in larger grains, and, in pressing, a larger proportion is retained in the cloths, while the serum or white water draining away is of a lighter color, with the net result that the yield of blood is better.
Pressing.
—The pressing is performed in the same manner as described for tankage, except that the material is handled dry. The waters from cooking, as well as from pressing, are saved for evaporation as tank water. Blood when pressed properly is “caked.” It should be broken up before being passed to the dryers.