When extraction is finished, the cocks H and H1 are closed, and the cock H2, which is connected with a cooling worm, is opened. The solvent is then evaporated, and regained by condensation. The oil is discharged, from the still through a pipe in the bottom provided with the cock H3.
The apparatus may also be so arranged that the still B is connected with two extracting vessels which are used alternately, while the contents of one are being extracted the other is emptied and refilled.
Fig. 14.
For working on a very large scale, Heyl's extracting apparatus, shown in Fig. 14, is very suitable. It consists of a battery of four or more cast iron or sheet iron cylinders, A1 to A4, communicating with each other and surrounded by steam jackets. The extracting vessels are so arranged that they can be emptied by tilting, which is rather inconvenient, as all the pipes have to be unscrewed. In each cylinder close above the bottom is a perforated plate covered with fine wire-gauze, upon which the material to be extracted is placed. The cylinder is filled to the top, and, after placing a similar plate upon it, the upper opening is closed by a lid suspended to a crane. The cylinder, as well as the lid, is provided with a broad flange, between which is placed a hemp tissue firmly pressed together by 12 clamps to serve for packing. After filling the cylinders with the material to be extracted and arranging the packing, the solvent (bisulphide of carbon) is conducted from a reservoir through the principal pipe, B, to the extracting vessels, and is introduced into A2 by opening the cock C2, which communicates with the pipe B. The bisulphide of carbon passes through the bent pipe D1, enters through the cock E2, below the false bottom of the cylinder A2, and, after penetrating the mass and filling the cylinder, runs through the cock C2 of the bent pipe D2, and the cock E3 into the cylinder A3, reaching the fourth cylinder in the same manner through the cock C3, the pipe D3, and the cock E4. From the last cylinder it passes as a thoroughly saturated oil solution into a reservoir, in which a vacuum has been created to promote the circulation of the fluid in the entire apparatus. After a quantity of oil solution corresponding to the contents of the cylinder A4 has arrived, the cock G4 is closed and the cock C4 opened, whereby the cylinder A4 is connected with A1 by the bent pipe D4 and the cock E1.
After the exhaustion of the contents of the cylinder A2, which is recognized by means of the glass tube H2 placed on D2 by the fluid running off being colorless, the cocks C1 and E2 are closed, and C2 and E3 opened, whereby the solvent runs into A3, and from there to A4 and A1; A2 being omitted. To effect this omission, and at the same time not to prevent the introduction of bisulphide of carbon, C1, C2, C3, and C4, are so-called two-way cocks, which, when placed in one position, connect the principal pipe B with the branch pipes D, but interrupt a further flow through the principal pipe B; while in the other position they close the pipes D and open the principal pipe B.
The cylinder A2 is, however, still filled with the solvent and material saturated with it. To remove the solvent, the discharge cock K2 on the bottom of the cylinder is opened, which communicates with the discharge pipe J, through which the bisulphide of carbon is conducted into a reservoir. The discharge is promoted by opening the cock M2, connected with the pipe L, and the admittance of compressed air, which displaces the liquid solvent. After the flow of the latter has ceased, the steam cocks on the jacket O2 and the cylinder P2 are opened under constant admission of air and simultaneous introduction of steam through the pipe N into the upper part of the cylinder.
The solvent (bisulphide of carbon) converted into vapor by the heat, is conducted together with the aqueous vapor, by the admission of air through the cock K2, the pipe J, and a cooling pipe placed between the extracting vessels and the reservoir, and collected in a reservoir to be re-used.
On account of the great volatility of bisulphide of carbon, considerable loss would, however, be incurred by the above-mentioned admission of air. To avoid this, the reservoir serving for the reception of the condensed bisulphide of carbon and aqueous vapor is closed, and connected by a pipe with a long, narrow, horizontal cylinder half filled with oil, and provided with a fan-shaft. The vapors of bisulphide of carbon entering the cylinder from the reservoir are absorbed, together with the air by the oil, the surface of which is constantly agitated by the fan-shaft, while the air, rendered entirely inodorous, passes out at the other end. The bisulphide of carbon is finally separated from the oil by distillation and again used.