In 1827, Messrs. Knowlys and Duesbury obtained a patent for improvements in tanning, having a similar object in view, and, as it appears to us, with an arrangement better calculated to succeed. The skins were to be suspended vertically in a large air-tight vat, which, as well as the skins, were to be com pletely exhausted of air, previous to saturating them with the tan liquor, which the skins will, in consequence, more readily imbibe. A large aperture, or man hole, is made in the to of the vat, for a workman to descend and hang up the skins, which are stretched from side to side upon hooks, at a regular distance apart, and kept in vertical and parallel positions by leaden weights, at their lower edges. This being done, a weak infusion of tan is admitted, until it covers the hides ; the workman then closes the man-hole by the cover, which is rendered air-tight by a proper packing upon its rebated edges; the air is next exhausted by the air-pump as far as may be deemed necessary ; in this state the vessel is to remain for a day or two, when the air may be re-admitted by a stop-cock, and the liquor pumped out through a pipe at the bottom of the vessel. The hides are then to remain to drain, and in contact with the air for a few hours, after which a second infusion of tan, stronger than that first used, is let in to cover the hides, and the process repeated as often as may be found necessary to completely tan the hides, increasing the strength of the liquors at every successive operation.
Our transatlantic brethren are not behind us in attempts to improve the old system of tanning. In the Journal of the Franklin Instants, we find the lowing specification of an American patent, granted to Ormond Cagswell, in 1831, which seems to be well deserving of the attention of the British tanner :— " The improvement consists in applying a solution of oak or other bark to hides or skins, in such manner, as that when the glutinous particles of the hide have absorbed and become mixed with the tanning or astringent principle, the other part of the solution (viz. the water) may pass off; and leave the hide free to receive more of the solution, and so on till it is tanned. The object is to expedite the process of tanning, and, consequently, to diminish the amount of capital necessary to be employed in the business. The apparatus, and mode is as follows : Make a frame of timber, of a square form; the width to e made as great as the width of the hides, parts of hides, or skins, that are to be tanned; the height and length to suit convenience. Near the bottom, or ground of said frame, a light floor is to be formed of the length and breadth of the frame; said floor to incline to one side, so as to carry off the liquor after it has passed through the hide ; the sides and ends to be raised from two to four inches above the floor, by fastening strips of plank on the inside of the frame; this will appear like a box,—say four feet wide, two inches high on one side, and four on the other, and twenty feet long ; (these boxes may be fixed one above another, about twelve inches apart, to the top of the frame ;) said boxes to be filled with sawdust, or any other soft porous substance that will not prevent the solution from running through the hide, and, at the same time, absorb and carry it off after it has passed through. On this surface (of sawdust) the hides, sides, or skins, (after having been prepared in the usual mode for tanning, except that the flesh is to be taken off clean,) are to be smoothly spread out, and, in order to keep on them a sufficient quantity of the solution, make sacks of coarse cotton or other cloth, an inch or more in diameter; fill them with the same material that the boxes are filled with, and place them around under the edges of the hides, which will raise said edges equal to the diameter of the sacks. After this is done, pour on
the hides as much of the solution as the hollow surface which they will then present will hold, and continue to fill them up as it runs off through the pores of the hide for the space of from three to fifteen days (the time in proportion to the thickness of the hide or skin), in which time they will be tanned, except the extreme parts or edges, which cannot be brought so fully under the process as the other parts of the hides; and in order perfectly to tan them it is necessary to lay them in vats after the common mode, for three or four weeks." In 1832 Mr. William Drake, of Bedminster, near Bristol, specified a patent "for an improvement in tanning hides and skins," the novelty of which consists in applying the tanning liquor on one side only of the skin, and causing it to ooze through the skin to the other side, whence the aqueous portion of the liquor is abstracted by cooperages; the results of which process are stated to be, that the skins are more thoroughly and uniformly tanned, and that the operation is completed with cold liquor in ten days instead of ten months. The specification states that the skins are to undergo the usual primary process of they are then to be immersed and well handled in a vessel containing backward (a weak solution of tan) until thoroughly saturated, which removes the lime and pre pares them for a stronger impregnation. Thus prepared, the skins (excepting such as are intended for butts and middlings) are to be rounded ; then two of them are to be laid face to face, and be carefully sewn together with waxed thread at their edges, so as to form a kind of bag impervious at the junction, leaving a small opening at the shoulder for the insertion of the neck of a funnel shaped vessel ; but the patentee observes, it would be better to sew between the skins a collar adapted to receive the end of the funnel. As bags so formed would bulge out when filled, they are to be confined between two gridiron like frames of parallel bars, adapted to compress the bag in such a manner as to produce internally a vertical stratum of liquid of about an inch in thickness between the two skins ; and as the skins are thickest towards their middles, this variation is compensated for by cutting away a portion of the vertical wooden bars from a straight into a hollow curved line. The skins are suspended by loops to the bags, which traverse the upper horizontal bars of the frames, and the two frames are duly drawn together by four screw bolts passing through the extremities of the top and bottom bars. The funnel being inserted into the aperture between the skins, it is charged with strong tan liquor sufficient to distend the bag, and leave a surplus quantity to supply the loss by evaporation after the moisture has penetrated to the outside of the bags ; a small gutter at the bottom of and between the frames receives whatever liquors may drop from the skins, and conducts it into a vessel, by which it is returned whenever neces sary into the funnel reservoir above. To prevent the compression of the ver tical bars from forming permanent indentations and ridges in the skins, the patentee directs that the bags be occasionally shifted a little laterally.