T A N 



88 



T \ \ 



the : stance when conden- 







Different tan- ibovf- 



ccsses, a.s wull as in those which 

 follow, and w':: the uctunl tanri 



jielt' into leather. O^k Imrk is 



i ommollly Used III Mlppb. 



coarse 



ami otlu-i 



157. Ill the 



of tanning, which is not vet entirely abandoned, the hides 

 and powdered Imrk WITI> laid in alten: in the 



tan-pit, which was then filled with water to the brim. 

 After some months the pit was emptied and re-filled with 

 fresh bnrk and water, ami this process was repented when- 

 ever the bark wi exhausted. In this way 

 the time hides varied, ac- 

 cording to their thickness and other circumstances, from 

 one to four years. The process has been groat h expc- 

 dited l)_v the improvements introduced in consequence of 

 the experiments of M. Seguin, a French chemist, which 

 arc detailed in Nicholson's Journal,' vol. i., p. 271 

 quarto sciies. published in the year 17!7 . of tanning 

 with concentrated solutions of Lark, formed by pass- 

 ing vwiter through a mass of powdered bark, until, by 

 suocessjvo infiltrations, it is completely deprived of its 

 soluble tanning principle. Scguin expected that, by the 

 use of very strong solutions, hides and skins might be 

 tanned in as many days as, under the old system, they 

 would require months: but these expectations have been 



imperfectly realised in practice, although the new 



11, which has been very extensively adopted, has 

 been productive of an important saving of time. With- 

 out entering into a minute investigation of the objections 

 to the use of concentrated tanning infusions, it may he 

 sufficient to state that, as observed by the late Sir Hum- 

 phry Davy, in hisvaluab!" paper on the operation of astrin- 

 gent vegetables in tau'uiig, published in the 'Philosophi- 

 cal Transactions' tor 1803, experience shows that 

 which are quickly tanned, by the use of strong solutions. 

 prod- of less (Unable quality than that which is 



' formed. Dr. I'rc. in reference to this important 

 point' t. of Arts, &X., p. l'22(i : The older tan- 



. ho prided themselves on producing a substantial 

 article, were so much impressed with the advantages of 4 

 slowly impregnating skin with astringent matter, that 

 they employed no concentrated in; ' in their 



iiatilicd the sKins with abundance of ground 

 bark, and covered them with soft water, knowing thai its 

 active principles a: 'nblc. and that, by being 



gradually extracted, they would penetrate- uniformly the 

 whole of the animal film--, in -lead of acting chiefly Upon 



dace, and making ! Micr, as the strong in- 



fusions never fail to do.' In illustration of these re; 

 he states that KXtlbs. of skin, quickly tanned in a - 

 infusion of bark, will produce l.'tTlbs. "of leather, while the 

 same weight of skin, slowly tanned in a weak soil 

 produce only 117^1 bs. ; the additional 19ilbs. in the for- 

 mer case lending to swell the tanner's bill, although it 

 deteriorates the leather, and causes it to contain I 

 the textile animal solid. Leather so highly charged with 

 tannin is. mop. -, as to allow moisture to 



pores : but the saving of time 

 -irons* temptations to the 



r to adopt tin- s\-teiu of tanning v.illi concent 

 infusions. 



The variations of practice among different tannei- 

 teud to the substance used as an astringent, as well as to 

 Hie manner of applying it. (Ironud oak-bark, which was 

 l\ material in common u-i 'ill the 



1 leather of a light-lawn 

 ' 

 imported forth. 



inclined to 



<ohdity and w 

 ml whi< 



from 



i the 





Xli., p. -I Ij. <ll!ll Is OUglH 



Mor. ' !iu. or terra ja- 



-iis to water. Another substance vvhu ! 

 used of late years is a kind of bonn-pod 



Till sc s!.|.st;inci ,.> imliv id -a'ty Or itl 



In the 



ning Some 



tanin ..i hers hot 



water or steam ; others at. 



ploy ooze,, or tanning liquid, which has been exhausted h\ 

 use. A I'm t her point of diffeiencc is found in ll 

 of the d. which 



the i: 1 -i of the hides v itii 



laying them ilat in the tan-pits, they are : 

 out to renew the solution ; and the skins 

 near the top of one pit arc laid near th- 

 next, so as to equalize the amount of hvd: 

 Sometimes the tannin;: is facilitated In snspendir 

 skins vertically in the liquid, by which 

 penetrated quickly: but the plan rcqui:- 

 room : and. unless the skins are freip 1 - 



sious injurious folds in the leather. Another plan, which 

 answers well for small light skins, that require i 

 time for tanning, is to sew up the skin into t; 

 a bag, to fill it with tan-liquor, and then immerse it in 

 the pit. The great space required is the principal o! 

 lion to this plan. In whichever of the above 

 tanning is effected, the hide is subjected to the "action 

 of solutions increasing PP 111 strength, until it 



is so perfectly penetrated, that when cut i 

 scuts a uniform brown colour: any appearance of n light 

 streak in the middle of its thickness bemoan indicati. 

 imperfect fanning. When the process is complete, the 

 hides are hung up in a shed, and allowed to dry slowly : 

 and. while they are (Irvine, they are compressed !>\ 

 ing or rubbing, or lr. them between rolfc 



irive- them firmness and \ vcl'ow dcpe 



how found upon the Surface of the leather, to which 

 the name of 'bloom' or 'pitching' is technic;. 1 

 and, although this depos:' .jucntly n 



the shoemaker in the operation of buffi:: 

 useless a. 1.1,! ion to the weight and cost of the leather, 

 the prejudice of pun quires that it : 



the si the tanner. According tu the 



tion of the ' Encyclopivdia liritanniea.' this N 



. the finer portion of tin from the interior 



of the skill, dissolved by the 



mains upon the surface by capillary attraction : and the 

 waste and deterioration occasion! .iidd 



be prev ente 1 bv the careful removal, by j if the 



exhausted ooze. 



Although, owing to the many differences in the pra> 

 of tanning, no definite time can be stated for the various 

 operations mentioned above, il may ! i that the 



uMial period required for tanning such h ; 

 for tin i.en's boots is from six to twelve mouths, 



and that from fifteen to eighteen months A d in 



.ng those of the thickest kinds, which a 

 butts It rema: noticing the 



r.g the thinner kin. 'her. 



to advert to some of the methods which h 

 contrived for ell'ecting a greater saving of time than 

 could bo accomplished by any . Men- 



tioned. 



Several schemes have been devised for fun-im; a tanning 

 solution tin. hide by m 



;:iued a patent in Isj 



:ianner : The hides, 

 after i . cleansed, and otlle. 



' manner, were to be . 



to sou: dental hole being then sewed Uj 



a.s to n ' u-hl. Three frames v 



prov ided of similar shape, and of such n form and si/e thai 

 when laid upon each other, with two I . i between 



might lie screwed to. 

 ing tin. eting ears, so that tbi 



a (hit water-tight chamber, circumscribed by t!. 



hen placed m a v ( rtical 



ii-liquor was introduced ' r or 



en the hides through a pipe inserted in the 

 .'.a me : the air being allo .'her 



pipe, which should be 



came filled with the liqu: -up- 



phed fioni an i required degree of 



hydrostatic the chamber; 



