The form of digester employed by Proctor and Ryland, of Birmingham, for extracting both fat and gelatine from bones, is shown Fig. 1027. It consists of a (duplicate) egg-shaped iron vessel a, capable of holding 6-7 tons of bones ; at the upper end, is a short neck b, surrounding the charging hole, which is closed by a tight-fitting cover ; here enters the steam-pipe a, which descends to the bottom of the digester, here also the waste-steam pipe has its exit. At the bottom of the digester, is a wooden false bottom e for supporting the bones, and on one side is a man-hole f for reaching the false bottom and removing the boiled bones. Cold water can be introduced by the pipe g. The liquid matters are withdrawn by the pipe h, separating into two branches, with appropriate taps the one i leading to a drain, the other k to a tank. The bones are first boiled in water by the admis sion of free steam ; when sufficiently boiled, steam is turned off, and time is allowed for the fat to separate ; cold water is then let in by g to raise the fat to the level of the pipe 1, when it escapes into a reeeptaele. The water is next run off from the digester by the pipes k i into a drain, the top cover is fastened down again, and the bones are steamed at a pressure of about 50 lb. for the extraction of the gelatine ; the gelatine is drawn off by the pipes b 4, and the bones are finally removed by the man-hole f. The bones are in a less friable condition than when the form shown in Fig. 1023 is used, and they require to heat somewhat before being ground.
(For a further and desirable process of purification, see Refining, p. 1460.) The calcining of bones has been described under the article Blacks—Bone-blaek, p. 453. One of the best arrangements for separating bone-oil from the other products of the distillation is shown in Fig. 1028. The pipes leaving the retorts first ascend, then bend downwards into a wide iron pipe, running horizontally about 1 ft. above the retorts, and containing water. Here the first con densation takes place. The vapours next pass by the pipes a to a continuous condenser b, such as is used in gas-works, and exposed to the enter air. Passing hence, the vapour, still containing condensable matters, is conducted through two coke scrubbers c, fed by a pipe q'with trickling streams either of water; or of ammoniaeal liquor, raised by the pump j from the well which receives it from the scrubbers, the liquor being thus made to circulate till it is sufficiently strong. The washed gas escapes at d for further treatment elsewhere. The liquors from the condenser c are received in f, where the first 'rough separation of bone-oil and ammonia-liquor takes place, the former floating while the latter sinks. The oil flows away at the surface by the 1-in. pipe w to a barrel v sunk in the ground ; the liquor escapes by the larger pipe g, which is bent siphon-like, and dips into the liquor below the oil, the top of the siphon being at the same level as the pipe that carries off the oil. The liquor is conveyed to the receiver h. it still contains much oil, which
is more completely separated by pumping the whole through the pipe i into a subsiding-vessel m, provided with taps as at y for drawing off the oil at intervals into v, while the liquor is pumped out through the pipe x (reaching to the very bottom of the tack) and pipe 1 into the still n. Its further treatment does not come within the scope of this artiole (see p. 232). The oil in v contains some ammonia worth recovering, It is therefore raised by the pump j into a tank a (Fig. 1029) above b, and the ammonia is washed out by injecting steam through the perforated pipe b; the liquor collects at the bottom, and is drawn off by c into a barrel d for conveyance to n or h.
The oil is variously dealt with. At some works, it is barreled and sold ; at others, it is mixed up with manures, or used as fuel. In the last case, it is pumped into a (Fig. 1029) and conducted by the pipe e, as wanted, to the boiler fire, into which it is showered by a steam jet issuing from f at g, at right angles to the opening of e, at the furnace-mouth. This seems to answer the desired eud very well. As the oil resembles mineral oil in some of its characteristics, it does not saponify readily, if at all, and is chiefly valuable as a coarse lubricant.
Vegetable Fixed Oils and Fats. —A detailed account of oil-mill machinery will be found in Spons' Dictionary of Engineering, p. 2482. It is here proposed to supplement it by the addition of such modern improvements as have since come into use. The class of machinery there shown in Figs. 5907 and 5908 is being rapidly replaced by the system introduced by Rose, Downs, and Thompson, of Hull, in 1874. Indebtedness is acknowledged to this well-known firm for the subjoined descriptions and illustrations of improved apparatus for extracting the oil from various oleaginous seeds and nuts, and converting the pulp into cake for feeding cattle.
The arrangement of the mill is shown in plan in Fig. 1030, and in elevation in Fig. 1031. The seed or other material passes through the following course :—It runs from an upper floor through the roll-frame A, by which it is crushed 3 or 4 times ; it is then taken by the elevators B to the kettle C, where it is heated and damped.
From beneath the kettle, it is drawn, in quantities sufficient to make a cake, by a box which conveys it to the moulding-ma chine E. Here it under goes preliminary com pression, the objects of which are (1) to increase the number of cakes which may be inserted in the presses at one time, enabling 18 12-lb.