ANNALS 



OF 



PHILOSOPHY. 



>' m^ ^DECEMBER, IQ25. - 



' • i n I- ' • J 



Article I; ;, 



0/z ^/ie Means of ascertaining the comparative Tanning Powers of 

 Astringents. By Mr. Edward Bell Stephens, Chemical 

 Assistant to the Royal Dublin Society. 



(To the Editors of the J.w;^««7.s of PMo5o/>Ay.) ' 



GENTLEMEN, f . h ^^^' ^'^^ ^^25. 



Of all the manufactures which depend on chemistry for 

 explanation and improvement, that of Leather, though highly 

 favoured by the attention of scientific men, is still, perhaps, 

 wzos^ in nefed'of th^ir aid.* ■ <^- i^/^- ^--> ^ ^ > ^ ^ ^^ 



Notwithstanding Seguin's happy discovery of t]ae_qhemical 

 affinity between tan and gelatine, which promised to introduce 

 something like analytic certainty into his art, the practical 

 tanner is yet unable to estimate the goodness of any bark 

 (previous to its actual use,) otherwise than by its exteriial 

 characters. He depends wholly on the colour, taste, and the 

 healthy bVittleness which in many cases requires an experienced 

 eye to, distinguish it from the brittleness produced by decay. By 

 the mere appearance he may indeed discriminate between 

 sound and. unsound bark of the same species; but when both are 

 fresh and healthy, or of different kinds (for instance, valonia and 

 cork tree bark), his eye and tongue no longer assist him in 

 determining the proportional worth of either. 



Any method therefore which would enable the tanner to 

 ascertain with speed and certainty the comparative value of 

 astringents (of which the market always affords a striking 

 variety) by the examination of samples, preuzotts to purchalse, 

 would be a great step towards rendering his business safe, 

 consistent, and regularly profitable ;^ and would, no doubt, be 



* A friend assures me that valonia (which is now much in demand amongst tanners 

 at 28?. a ton) was offered to them from Italy, SO years ago, in any quantity, at 4Z. a 

 ton, in vain: they had no means of ascertaining its value experimentally. 



New Series, \0L. X, 2 d 



