TAN'NING MATTER, <ScC. 27 



6 



The whole of the artificial tanning substance was ex- Experiments, 



tr.icted by diifcrent portions o^ water, and the remainder f,ci*ai substance 



of the bark thus exhausted, was again treated in the man- having t he cha- 



aer above* described, and asrain alForded a considerable ''peters of tan- 



' ° nmg matter. 



quantity of the tanning substance, so that these processes 



evidently might have been continued until the whole of 



the bark had been converted into it. 



This might also have been accomplished, if in the first 

 instance, the exhausted bark had been converted into 

 charcoal, and digested in nitric acid, as described in my 

 first Paper ; but then, the effects would have been more 

 slowly produced, and much more nitric acid would have 

 been consumed. I am now therefore fully convinced, 

 not only by the results of the experiments related in this 

 Paper ; but also by many others which it would have 

 been superfluous to have stated, that the most speedy and 

 most economical of^all the processes which 1 have des- 

 cribed, is that of treating roasted vegetable substances in 

 the way which has been mentioned, and considering that 

 all refuse vegetable matter maybe thus converted into a 

 tanning substance by means the most simple, and without 

 any expensive apparatus, I cannot help entertaining much 

 hope, that eventually this discovery will be productive of 

 some real public advantage. 



§ V. 



In my first Paper I have remarked, that I suspected 

 the tannin of the peat moors to have been produced du- 

 ring the imperfect carbonization of the original vegetable 

 substances. Whether this has been the case, or whether 

 the tannin has at times been afforded by heath and other 

 vegetables growing upon or near the peat, still appears to 

 me to be uncertain ; but whatever may be the origin, I 

 never have yet been able to detect any tanning substance 

 in peat, although I have examined a considerable number 

 of varieties, some from Berkshire, and many from Lanca- 

 shire, which were obligingly sent to me for this purpose 

 by my friend John Walker, Esq. F. R. S. Mr. Jame- 

 son has also made the same observation,* so that there 



* An Outline of the Mineralogy of the Shetland Islands, &c. 

 8vo. edition, p. 174. 



^ 2 cannot 



