1815,] Ohervatlons on Tanning. 113 



you the results of experiments I have instituted on this branch of 

 our manufactiires. 



Respecting the question whether lime-water or pure river wafer 

 extracts the tannin from oak bark most promptly and in greater 

 quantity, experiment enables me to decide on the latter. 



That 'lime and alkalies ought to be discarded in the process of 

 tamiing (could we find a substitute for the former) will aj)pear 

 evident from immersing a piece of leather in either j the fluid will 

 appear in a few minutes of a hhod-red colour, and the surface of 

 the leather blackened; a proof that the tannin has been absorbed by 

 the alkaline menstruum, or lime-water. 



Heuce tlie justice of the remark, by all possible means gg/rzrf of 

 the lime employed in depilation, previous to irmnersion In the 

 tannin ooze. Lime will always produce with tannin an abundant 

 and difficultly soluble precipitate : and for the same reason alkalies 

 must not be used in raising the pelt, as they, though producing a 

 quick and powerful extract, prevent the union of the tannm with 

 animal gelatine by virtue of superior affinity. 



The excrement of the pigeon and hen were tried with respect to 

 their superiority over that of other animals. By sulphuric acid, a 

 powerful elTervcscence takes place ; and as lime had been proved to 

 exist by the previous application of fluate and oxalate of ammonia, 

 the CQr/w;ic ffci^ was inferred to be in combination, and not the 

 phosphoric, as the precipitate by barytes did effervesce by muriatic 



acid. 



Nitro-77inriaie of tin and gelatine threw down an abundant pre- 

 cipitate. Hence I presume that it is to this peculiar substance, and 

 not to any of the salts wliich i. contains, we are to attribute its 

 action on the pelt. The gelatine must be rendered less pliant by, 

 the lime used in depilation. The substance in question haying an 

 affinity for lime, would necessarily render the fibre of the hide less 

 rigid than before, by removing the cause. 



I have long suspected that handling did more for the beauty and 

 value of the leather than was suspected. I endeavoured to ascertain 

 to what this effect was owing. For this purpose a piece of leather 

 was suspended in a vessel filled in water over the shelf of a pneu- 

 matic cistern, while the water was displaced by a stream of oxygen. 

 The leather was in consequence beautifully bloomed, and this elicct 

 penetrated quite through the piece. 



Diluted Jiitric acid stains the leather of a Hood-red. 



Sulphuric acid acts in an inferior degree, and makes thekather 



Muriatic, oxymuriatic, citric, phosphoric, acetic, and fluonc 

 •cids, communicate each a bloom. Of these the oxymuriatic and 

 muriatic niidi arc by far \hc pnjeraUe. 



Oxymuriatic acid and whcatcn flour communicate a very fine 

 light bloom. 



It was therefore of considerable moment to ascertain whether the 

 effect was owing to the fecula or gluten of the flour e^nployed. 



Vol. V. N<^ ll. H 



