The extracting vessels, A and B, are charged with bones, all the cocks, with the exception of M and N closed, and the air-pump, L, is set in motion, whereby a vacuum is formed in A. When this is sufficiently large, water is admitted from H through the cock O into the space P. The water-cock is then closed and the steam-cock, Q, opened. The steam entering the space, R, brings the water in P to the boiling-point, and the air-pump sucks off the steam formed after the cock, N, is opened. The air-pump is then stopped and all the cocks closed, except S. The solvent now passes from the vessel, K, into the space P, and after closing the cock S, is evaporated by the admission of steam into R. The water-cock is then opened and cold water admitted into the jacket C, the solvent saturated with fat being thereby condensed in P. The water is then discharged from C and steam introduced into R1, whereby the solvent is evaporated and forced into the extracting vessel B by means of the air-pump, L, after closing the cocks M and V.
The process is then repeated in B, after a vacuum has been created in the same manner as in A.
In the meanwhile the vacuum in A is interrupted by opening the air-cock F and the fat drawn off through P by opening the cock U.
The bones freed from fat are removed through the manhole D, and A is charged with fresh material while the operation is carried on in B. Thus the operation is continuous, the solvent passing without any loss whatever from one extracting vessel to the other.
Fig. 39.
Alfred Leuner’s apparatus. Fig. 39, works on the Soxhlet principle, without pressure, using solvent and steam simultaneously. The bones are placed in A above the perforated false bottom B. D is a steampipe by means of which the bones are steamed as a preliminary, the surplus steam escaping through the outlet pipe E. After steaming, water and benzine are run in from the reservoir F, into the space under the false bottom, and heated by the steam coil P. The vapors evolved are condensed in the worm K, and at first run back over the bones through the cock L, the vapor passing upwards to the worm through R, and the condensed liquid being divided into separate streams by the spreading plate O. After some time the cock G is opened so that the condensed liquid runs into the reservoir F, instead of flowing back into A. When all the solvent has volatilized nothing but water condenses in the worm, which is known by means of a sampling cock attached to A, the draw-off cock E is then opened and the watery gelatinous solution and oily matter run off into a suitable separating receptacle. The bones in A are then discharged through a manhole, and A being refilled, the whole operation is repeated.
Extraction with hydrochloric acid. If the bones are to be chiefly worked for glue, extraction with hydrochloric acid, which has been referred to in Chapter III, under “Bones and Cartilages” may be highly recommended, the bones being thereby freed from their mineral constituents and the glue-yielding substance remaining behind in a pure state. The bones are allowed to remain in contact with the acid till they are flexible and translucent. This may be readily recognized by laying upon the material in the vat a bone split in two. When the latter by the treatment with acid shows the characteristic appearance of swollen cartilage, i. e., has become translucent, extraction may be considered complete.
The solution is then drawn off through a tap immediately above the bottom of the vat into stoneware vessels, and conveyed to the evaporating pans. The tap is then closed and enough water to cover the cartilage is admitted into the vat, and the whole allowed to stand for a few hours in order to extract as much as possible the solution of bone-salts remaining in the cartilage. The fluid is then drawn off. It is a quite concentrated solution of bone-salts and, mixed with an equal volume of hydrochloric acid, may be used for the extraction of fresh quantities of bones, or be mixed with the fluid first drawn off and evaporated.