DIGESTER. A name originally applied to a strong boiler. with 41 closely fitting eover, in which bones or other animal substances, placed in water.eould be raised to :1 troperntur above the boiling point. or 212° F. The word is now given a wider meaning: the material may be placed in some liquid other than water, and chemical action instead of heat may be used to effect the disintegrating process. The digester. in its -Mildest form, was invented in by Denis Papin (q.v.), a French scientist. It is of iron or other metal. and has an airtight cover. provided with a from which steam may be allowed to escape when the pres• sure becomes too great. The increased pressure to which the Of the boiler are exposed rais•s them to a much higher temperature than could be secured in all Open reaching at time- 400' F. .\1 such a temperature bones will dissok•. In it modern forin• the lapin digester is put to lunch Wider t11111 the Mere prep• aration of soup and extraction of gelatin from hones, for which it was originally intended. One application of the ion the lard IIr grease tank. whirls is all es•enlial feature of a large modern "la ilgillet-bou,c. tutu cm+ tanks the carea•ses of animals too poor for the regular market and the entrails and grease•yielding offal of other animals are thrown. Steam is applied, which resolves the content, of the tank into fit; water, which contains much soluble matter in solution; and mud, containing earthy and solid particles, the contents arranging theIllSelVe. in
layer., top to hott0111, in the order named, according to their specific gravity. The tank is usually a vertical cylinder, with a perforated false bottom, which holds the charge and at the saint. time allows the water of condensation to percolate into the lower chamber. There is a discharge hole at the bottom for removing the l'esid1111111, and a 11111111mq' of try•eoeks a re a r ra nged along the sides, by Means of which the level of the fats and water may be ascertained. There may be two discharge cocks; through the higher one the limiting fat may be decanted and through the lower one the water may he drawn till, as the t011iellts and state of the process require. In some forms of digesters, like those for treating garbage, the water and grease may be drawn oil' together, and separated afterwards. The solid matter, called tankage. may be pressed or dried, or both, and is oftentimes utilized for yigiohs pin-loses.
A familiar example of a chemical digester is the apparatus for t•stra•ting tannin from nut galls by means of ether. The nut-galls are placed in a vessel saturated with ether; the volatile extract falls into a closed vessel placed below and connected by means of a pipe with the top mf the other vessel, to prevent the escape of the ether.