TAiNNING. 



barks of okl trees. (Pliil. Traiif. 1803, p. 264.) From 

 thefe obfervatioiis, founded 011 cxpcrimeiils, Mr. Hatchctt 

 infers that, there is an intimate coinieftion between the form- 

 ation of new wood and the formation of tannin in fuch ve- 

 getables as afford the latter ; and this idea is corroborated 

 by the chemical nature of thofe fubitances. 



It has been fuggcfted that the extraftive matter found 

 in barks, or in lubRances ufed in tanning, affetts t<ic 

 colour, if not the qtiahty of leather. Thus, (kin tanned 

 with gall-nuts is much paler than (kin tanned with oak bark, 

 which contains a brown extraftive matter. Leather made 

 from catechu is of a reddidi tint. 



It is found that the precipitates obtained from infu- 

 fions containing this principle or tannin by ilinglafs, when 

 dried, contain at a medium rate about ^o per cent, of vegetable 

 matter ; and that it is eafy to obtain the comparative value 

 of different fubftances for the ufe of the tanner, by com- 

 paring the quantities of precipitate afforded by infufions of 

 given weights mixed with folutions of glue or ilinglafs. 

 In order to make experiments of this kind, an ounce 

 or 480 grains of the vegetable fubftance in coarfe powder, 

 fhould be a<il:ed upon by half a pint of boiling water : the 

 mixture (liould be frequently ftirred, and fuffered to ftand 

 twenty-four hours ; the fluid fhould then be paffed through 

 a fine linen cloth, and mixed with an equal quantity of folu- 

 tion of gelatine, made by diffolving glue, jelly, or ifmglafs 

 in hot water, in the proportion of a drachm of glue or ifm- 

 glafs, or fix table fpoons full of jelly, to a pint of water. The 

 precipitate is to be collected by pafTmg the mixture of the 

 folution and infufion through folds of blotting paper, and 

 the paper expofed to the air until its contents are quite dry. 

 If pieces of paper of equal weights are ufed, in cafes in 

 which different vegetable fubilances are employed, the dif- 

 ference of the weights of the papers when dried, will indi- 

 cate, with tolerable accuracy, the quantities of tliis principle 

 or tannin contained in the fubftances, and their relative value 

 for the purpofes of manufaflure. 



TANNING, the art of converting the gelatinous part of 

 the (kins of animals into the fubftance c.illed leather, by im- 

 pregnating it with tannin or the tanning principle, in fuch a 

 manner as to render it tenacious, durable, and impermeable 

 to water. 



It is difficult to fay at what period the art of tanning was 

 difcovered. It was doubtlefs known to the ancients in fome 

 degree of perfeftion ; and it is highly probable that the (l<ins 

 of animals were employed by man as a covering long before the 

 art of tanning was known : but they would require in this 

 ftate to be conftantly kept dry, as moilfure would foon 

 bring them into a ftate of putrefaftion. 



The aftringent matter, which converts the fkin into leather, 

 abounds in io many vegetables in every country, that ac- 

 cident w^ould foon lead to fome method of producing the 

 change. Independent, however, of vegetables, many earthy 

 and metallic fubftances have the property of rendering fl<ins 

 incorruptible to a certain extent ; and fome mineral waters 

 containing copper or iron will occafion this change. 

 Hence we may conclude that fome means of giving prefer- 

 vation to the fldns of animals muft have been known at a 

 very early period. 



Though there has been no radical alteration or any great 

 praftical improvements in the art of tanning, yet /or the 

 laft twenty or thirty years it has attrafted the attention of 

 many celebrated chemifts and philofophers in all countries, 

 who have inveftigated the fubjed with great accuracy and 

 precifion. Previous to this period we occafionally find fome 

 experiments and obfervations by men of fcicncc on the ma- 



terials of tanning, as by the Hon. Charles Howard in 1 674, 

 (Phil. Tranf. vol. ix.) by the abbi- Nollct, Gefncr, Glc- 

 ditfch, Buffon, dc la Lande, and others, in Mem. Acad. 

 Sc. Paris and Berlin. 



In the year 1765, the Society of Arts and Sciences in 

 Loudon granted a premium of loc/. for the difcovery of 

 a method of tanning with oak faw-dull ; and in i 795 the 

 Rev. G. Sw.iyne fuggeilcd the ufe of oak leaves. It in 

 unqueftionably true that all thofe fubftances, and indeed 

 every part of almoft every vegetable in nature, poffeffes a 

 certain portion of the tanning principle ; Jjut, exciufive of 

 oak b;u-k and two or three other well-known articles, the 

 quantities of all tlic reft added together would be fo incon- 

 fiderable, and the proportion of tannin contained in them 

 fo inadequate to the purpofes of manufacture, that, except 

 for philofophical curiofity and chemical experiment, tiicy 

 are unworthy of notice. As the theories of fpeculative 

 minds lliey are ingenious and amufing, but they afford very 

 little uieful information on the nature and properties of 

 tannin, and have produced no beneficial refults in practice. ' 

 ■ Deyeux, about 1793, (Annales de Cliimie, vol. xvii. ) 

 appears to be the firfl chemift who fucccfsfully explained 

 the true principles of tanning ; which afterwards, witli more 

 praftical application, were ftill further developed by the 

 labours of M. Seguin in 1795. Before his invelligation of 

 thib fubjeft, the theory of tanning was ftriftly mechanical. 

 The aftringency of vegetables, which produced tlie change 

 in the flcin, was confidered as a refinous body, which had the 

 efteft of giving firmnefs to the fibres of the (kift, and render- 

 ing it infoluble. 



Seguin faw the operation in a chemical point of view : 

 he examined the nature of the procefs fcicntifically, and 

 difcovered that the cliange which the fl<in underwent in 

 the operation of tanning, was the refult of a chemical union 

 between a fubftance funiiihed by the vegetable employed, 

 and the gelatinous part of the ilvin. Thefe principles be 

 confirmed, by combining the vegetable fubftance in queftion 

 with the gelatine of a folution of ifinglafs. 



It will be feen, from our article Tannin, that the com- 

 pound difcovered by Seguin, and which is precipitated when 

 an infufion of nutgalls is added to a folution of ifinglafs, is 

 an infoluble fubftance, having many properties common to 

 leather. See Nicholfon's Journal, vol. i. p. 271. 410. 



The praftice which M. Seguin founded upon his theory 

 was generally admired. He firft extrafted the tannin from 

 the vegetable, which was oak bark, and applied it to the pre- 

 pared ft<in in a more concentrated form, with a view to im- 

 pregnate it as fpeedily as polfible with the tannin. This was 

 laid to be done with great fuccefs in one-third of the ufual 

 time, and to have produced fuperior leather. The lame of 

 this difcovery foon fpread throughout Europe, and Mr. 

 Dcfmond, a man of education and intelligence in this fountry, 

 took out a patent for the exciufive right of ufing M. 

 Seguin's method of tanning. 



Although this procefs of fufpending the hides vertically 

 in a very ftrong folution of bark f'aved much time, yet it 

 was foon found to be adapted only to the thickeft hides 

 ufed for fole leather, and quite unfit for the lighter kind of 

 fl<ins which required flexibility and tenacity. This method, 

 therefore, of Seguin's, however chemical ajid philofophical 

 it might appear, did not anfwer in the refult ; and as it 

 was attended with mucli additional expencc, has never been 

 generally praftifed in England. 



It was not, however, till 1803, when fir Humplirey 

 Davy (a name ever to be recorded in the annals of fcicnce 

 with gratitude and admiration) began to invcftigalc the fub- 



jcdl, 



