possesshig the Properties of Tann'm. \bO 



seems almost evident that this tanning substance is formed 

 in consequence of part of the oxvgeu of the nitric acid be- 

 coming combined with the hydrogen of the original body, 

 so as to form water; and the carbon, being thus in some 

 measure denuded, is rendered capable of being gradually 

 acted upon by the nitric acid in a manner nearly similar to 

 that which takes place when it has been previously converted 

 into coal. 



The colour of the precipitates which this tanning sub- 

 stance yields with gelatine is constantly pale or deep yellow, 

 whilst that of the precipitates formed by the first variety is 

 always brown ; I am therefore induced to believe that the 

 different colours of the precipitates produced by the varieties 

 of tannin depend on the state of their carbon. 



When resin and the other bodies were treated as above 



formation of nev/ wood and the formation of tannin in such vegetables as 

 afibrd jhe latter; and this idea is corroborated when the chemical nature of 

 tlicie substances is considered- 



From experiments made on the ligneous substp.ace of vegetables, or the 

 woody fibre, it appears to be composed of carbon, oxyjjen, hydrog^eu, and 

 cilrogen; but of these its principal and essential ingredient is carbon. 



In like manner carbon is unquestionably the basis and principal ingredient 

 of tannin. Considering, therefore, that both of these substances consist prin- 

 cipally of carbon ; that tannin is secreted in that part of barks where the 

 formation and deposition of new wood take place; and that the quantity of 

 tannin is the most considerable in young trees, and seems thcrefoi e to keep 

 pace with their more vigorous growth, and consequent rapid formation of 

 wood; it appears very probable that those vegetables which contain tanain 

 have the faculty of absorbing more carbon and of the other principles than 

 are immediattly required in the formation of the different proximate vege- 

 table substances, especially the woody fibre: that this excess, by chemical 

 combination, becomes tannin, which is secreted in the wliite interior bark : 

 that in this state it is a principle peculiarly fitted to concur by assimilation to 

 form new wood: that it is therefore subsequently decomposed at the prope* 

 period, and is employed in the formation of the new wood : that there is not 

 a continual accumulation of tannin in the vegetables which afford it, as it is 

 successively formed in and with the white cortical layers, and i> successively 

 decomposed by concurring to form new wood : and, lastly, that as the vege« 

 table approaches more nearly to the full maturity of its growth, when wood 

 ii less rapidly and less plentifully formed, so in like manner less tannin is se- 

 creted; for, the fabric being nearly completed, fewer materials are required. 



Such I am inclined to suspect, from the facts which have been adduced, to 

 he the cause and mode by v.'hich tannin is form'.'d in caks and other vegeta- 

 bles; but I make this statement only as-a probublc cwnjeclure, which may be 

 refuted or coufirmed by future ebgcrvatiuDt. 



described 



