62 Ohrrva lions on the Processes of Tannin cr. 



extract of the wood of a species oF the mimosa, which o-rou-^ 



Sc mnn h^"^ •^''''i' ' ^-^ -^^-^-^S on its price, and oa 

 tlic quantiu.c ,a ^1,,,.,, „ ,„,,^. ,,^. p.^eurcd, there is e;reat 

 reason to beucve i\.^i \, „,.,,, i,,. „,*, i i . i • ? . 



'I m.iy be made a valiiab e article of 

 commerce. '^ ^^ 



In a paper published in the I'Iiul.. , . . „ 

 for 1803 *, a statement is given of the Jo'mpL. '/"'^''^'^f'""'^' 

 different astringent substances, oak bark being eoii}';"'* ^, 

 as the standard. 



The attraction of tannin for water is much stronger than 

 that of any otlicr of the principles usually found in astrin- 

 gent vegetables ; and the saturated infusions obtained from 

 substances containing very different proportions of astrin- 

 gent matters, are usually possessed of the same degree of 

 blrentrth with regard to tlieir tanning powers. 



When saturated solutions of the tanning principle are 

 used in the process of manufacture, the leather is tanned in 

 a much shorter time than in the common operation with 

 weaker infusions. The rapid njethod of tanning has been 

 recommended bv Mr. Scguin ; and is ably described in a 

 pamphlet published by Mr. J3csmond. 



It has however been generally observed, that leather too 

 quickly tanned is more rigid, and more liable to crack than 

 leather slowly tanned. And there is every reason to be- 

 lieve that its texture must be less equable, as the exterior 

 strata of skin would be perfectly combined with tannin be- 

 fore the interior strata were materially acted upon ; and the 

 want of colouring or extractive matter in the strongest lixi- 

 vium, in many cases must affect the nature of the leather. 



The substances used for tanning should, in all cases, be 

 preserved in as dry a state as possible before they are used. 

 When they are exposed to moisture and air, the tanning 

 principle by degrees is destroyed in them, and for the most 

 part converted into insoluble matter. 



Tlie process of drying bark by heat, when carefully con- 

 ducted, must, as there is great reason to believe, on the 

 whole be advantageous. The tanning principle is not de- 

 composed at a temperature below 400*^. And in fresh ve- 

 getable substances, tannin appears to be sometimes develop- 

 ed or formed by the long application of a low heat : this 

 fact I observed with niv friend Mr. Poole in Septembcv 

 1802, with regard to acorns; and I have since made the 

 same remark upon the horse chesnut. 



'■' Ste our next articL. 



vni. Ju 



