=Animal Feeding.=--Experiment has also shown that nitrogenous products have a very high value as a nutritive food for growing and fattening animals, so much so in fact, that in many agricultural districts the entire output of tankage from local packing houses is now sold in the immediate neighborhood for stock foods. Under various names evaporated tank water is an ingredient of these. =Tank Water.=--Invisible but in considerable quantity, nitrogenous solids were formerly lost in the various waters from cooking, but they are now collected and reduced to a semi-solid, or solid form. These are classified under the one broad name of tank water, but they include almost any water in which animal matter is cooked unless the water be of such character that it can be used for edible purposes. The chief sources of supply are rendering tank water, blood water, bone house cooking water, ham and tripe boiling water, etc. It is estimated that any water showing density of ¹⁄₂° Beaume scale is worthy of concentration. _Keeping Water Concentrated._--Evidently the more dilute the water, the more water it is necessary to evaporate, and hence more costly to concentrate. In raising the tanks so as to flow the oil from the tank cocks, it is necessary at times to admit fresh water. To avoid this the water from one tank is usually transferred to another of the same character by use of a pump. _Collection of Waters._--After the tankage has been dumped into the skimming box and all grease skimmed off, the tank water should be drawn into a separate vat. The “press water,” which is the water from the pressing of the tankage, should also be collected. The floor drainage except from the tank filling floor, and practically all water produced in the tank house, should be collected; in fact, some operators go to the extreme of not connecting the tank house sewer system to the city sewer so as to intentionally preclude the wasting of water. =Preparation of Solids.=--The tank water is collected in large vats for processing. The solids or sludge is undesirable to handle, consequently in draining the tank water from the surface vats into the storage, it is necessary to have the holes of the screens in the surface vats reduced to about one-quarter of an inch in size in order that all of the solids will be retained in the surface vats and not be permitted to go into the tank water catch basins.