T A N 



39 



TAN 



the effect of which was to distend or swell out the sides, 

 and to force the liquid through the pores of the skins, 

 it making its appearance OH the outer sides like drops of 

 dew or perspiration. When the leather appeared to be 

 sufficiently tanned, the liquor was drawn off by a stop- 

 cock, the frames were unscrewed, and the compressed 

 edges of the hide were cut oft'. Spilsbury's process was 

 soon abandoned ; the reason of its failure being, aecord.- 

 ing to the author before quoted, in the ' Encyclopaedia Bri- 

 tannira,' that a large excess of tannin dissolves gelatin ; so 

 that taunate of gelatin was found on the outer sides of the 

 skins in the form of long masses of slime, while the leather 

 had lost much in weight, was very porous, and unequally 

 tanned, in consequence of the tun-liquor penetrating most 

 readily the thinnest or weakest parts of the hide. The 

 error of the principle of this method not being generally 

 understood, several similar plans were subsequently con- 

 trived by different persons ; but these, or most of them, 

 have been found unsuccessful. Of these, allusion may be 

 made to the process patented by Mr. Drake, which con- 

 i in sewing two skins together (after they had re- 

 ceived a slight tanning in the ordinary way), so as to form 

 a watfr-tight bag, which was filled with tan-liquor. The 

 bag thus formed was compressed between two vertical 

 gridiron-like frames or racks, by which it was prevented 

 from bulging at the sides, and the liquor was confined to a 

 thin vertical stratum. As in the last process, the aqueous 

 portion of the tan-liquor percolated through the hides ; 

 and this penetration of the leather was facilitated by 

 heating the room so as to promote evaporation from the 

 exterior surfaces of the bags or skins. To prevent the 

 bars of the racks or frames from producing permanent in- 

 dentations in the leather, it is necessary to shift the bags 

 a little occasionally during the process. In another some- 

 what similar plan, contrived by Mr. Cox, the hides were 

 to be sewed up in the form of bags, and supported by a 

 casing of canvas ; and in the process of Mr. Chaplin, the 

 bags were laid in an inclined position, and turned periodi- 

 cally to equalize the action of the tan. With every pre- 

 caution however, it is difficult to tan a hide equally by any 

 such process ; and the objection urged against Spilsbury's 

 plan applies to nil the modifications of it. In another 

 plan, which has been tried under several forms, the tan- 

 ning liquid is applied to both sides of the hides, which are 

 E laced in an air-tight vessel, and is forced into their pores 

 y hydrostatic pressure, the air being previously pumped 

 out. The operation may be repeated ;H often &s in d 

 with infu-ions gradually increasing in strength ; air being 

 allowed to fill the pores of the hide between each immer- 

 sion. Another plan which may be alluded to here is that 

 of an American tanner, Osmond Cagswell, described by 

 II 'bert (Engi/i \Ji'i-liiniir'x i./i<-i/rl',],ffdin,^o\.\\., 



p. 04), from the 'Journal' of the Franklin Institute. It 

 consists in laying; the hides upon a quantity of sawdust, 

 contained in shallow boxes, of which any required number 

 may be arranged in a suitable framework, about twelve 

 inches above one another. The hides are not laid fiat, but 

 have their edges a little raised, so that their upper surfaces 

 form shallow troughs capable of holding a layer of the 

 tanning solution, which must be replenished from time to 

 time as it filters through the hide and the sawdust, or 

 other soft, porous substance upon which it is laid. The 

 spent liquor runs off' from the bottom of the box or trough, 

 which is somewhat inclined for that purpose, into :i 

 or channel provided for it. -The improvement consists, 

 according to the specification quoted by Hrbert, ' in ap- 

 plying a solution of oak or other bark to hides or skins in 



i manner as that when the glutinous (gelatinou 

 tides uf the hide have ab-nrheil and become mixed vutl 

 the tanning or astringent principle, the other part of tin 

 solution (i.e. the water) may pass off, and leave the hidi 

 free to receive more of the solution ; and so on till it i*> 

 tanned.' The operation was performed, it is stated, in a 

 very short time ; but as the outer parts or edges of tin 

 hides were not perfectly tanned by it, it was necessary to 

 immerse them in vats in the usual manner for tnret 

 or four weeks, to complete the process. If the principle 

 were iound to be. advantageous, this, which forms ; 

 ' defect in Mr. Cagswell's scheme, might be readily 

 avoided. 



Still more recent than any of the above-mentioned plan 

 . Herepath and ( 'ox, of Bristol . 

 which, an far as present experience can show, appears to 



fleet the desired object very completely. Their process, 

 which was patented November 16, 1837, is founded upon 

 he principle of washing a sponge, by alternately allowing 

 t to imbibe water, and then forcibly expressing it. In the 

 )ld system of tanning, the hide may be compared to a 

 ponge, which, after being saturated in a weak solution, is 

 emoved to a stronger, without the fluid contained in its 

 >ores being squeezed out ; while in the new plan the weak 

 illusion, or ooze, is forced out of the pores of the hide be- 

 bre it is subjected to a stronger, so that the fresh ooze 

 may be able to act more efficiently. This is effected by 

 connecting a number of hides together by strings, so as to 

 'brm a continuous belt, and passing them between rollers 

 .urned by steam or other power, while they are being re- 

 moved from one solution to another. In order to produce 

 a tolerably uniform belt or continuous sheet of hides, they 

 are either placed alternately head to head and tail to tail ; 

 or, if laid across the belt, with the heads and tails towards 

 each side alternately. In one of the arrangements de- 

 scribed in the specification, the hides are united into an 

 endless band, and are always passed between the rollers 

 of which a pair is erected over each pit) in one direction ; 

 Kit in another plan the ends of the belt are not connected 

 :ogether, and the motion of the rollers is reversed when 

 necessary, so that the belt of hides may be delivered into 

 .he tan-liquor alternately on each side of the apparatus. 

 The latter arrangement is that described in the recently 

 published article in the ' Encyclopaedia Britaunica,' from 

 ffhich the following details are derived. The lower roller 

 s about thirty inches in diameter, and is covered with 

 Horsehair cloth ; and the upper roller, which is pressed 

 igainst the lower one with any determinate degree of force 

 by means of weighted levers, is only about eighteen inches 

 in diameter, and is covered with woollen cloth. By this 

 process a strong hide may, it is stated, be tanned through 

 in from one to two months, and calf-skins and hips (the 

 hides of young cattle) in from twenty to thirty days. 

 Double the usual quantity of work is performed ; one-half 

 of the capital required in the common process is rendered 

 unnecessary ; the saving on bark, labour, and general cost 

 of manufacture is about 1J'/. per Ib. ; and the increase in 

 the weight of butt leather, as compared with that made in 

 the usual way, is as 34 Ibs. to 28 Ibs. The very thick hides, 

 known as ' butts,' when prepared by the patent process, 

 are sent to market within four months from the time of 

 their delivery in the tanner's yard ; and the profits arising 

 from quick returns, great weight of leather produced, and 

 reduced cost of production, are stated to be eight times as 

 great as upon the old plan, the prices of hides, bark, and 

 leather being the same. It should be further observed that 

 the leather made in this way is more elastic and imper- 

 vious to water than any other. 



Although the general principles involved in the prepa- 

 ration of all kinds of leather are the same, and some of 

 the processes above described are performed with little 

 variation upon the skins of smaller animals as well as upon 

 the thick hides of various kinds of oxen, the precise course 

 of operations requires many modifications which cannot 

 be here described. Of the preparation of several of the 

 lighter and more ornamental kinds of leather, a familiar 

 account is given in No. 652 of the ' Penny Magazine.' 

 which is devoted to a sketch of the processes followed at 

 one of the great leather-manufactories of Bermondsey. 

 \Ve have- hitherto alluded chiefly to the preparation of the 

 thick hides used for sole-leather, among which several 

 varieties may be found, each distinguished by a different 

 technical name, by which its thickness, quality, or mode 

 of preparation is known ; but the thinnest and weakest, 

 hides, as well as the skins of calves and other animals, are 

 aUo prepared for use as upper-leathers, in which case it is 

 itary to reduce their thickness by shaving or paring 

 them down upon the flesh or inner side, before they are 

 subjected to the action of the tanning infusions. Such 

 hides or skins also require, after leaving the hands of the 

 tanner, to be nibbed, softened, and dressed by the currier, 

 in order to bring them to the necessary degree of flexibility 

 and smoothness. The currier also has recourse to shaving 

 or paring with a peculiarly formed knife, to bring the skin 

 to the requisite tenuity; and it is his office to blacken 

 tin- surface, which, for common shoe-leather, is done on 

 the flesh side, although for some purposes leather is 

 blackened upon the outer or grain side. Horse-hides, 

 which are comparatively weak and thin, are sometime* 



