222 



still continued to yield the tanning substance, our author thinks it 

 probable the process might be repeated until the whole of the bark 

 became converted into the above substance. 



From the foregoing experiments, and many others made by him, 

 Mr. Hatchett thinks that the method of treating roasted vegetable 

 substances here described is the most speedy and economical for 

 obtaining the artificial tanning matter ; and, as all refuse vegetables 

 may be thus converted into that matter by simple and unexpensive 

 means, he hopes the discovery may eventually be productive of some 

 real public advantage. 



In a former paper Mr. Hatchett observed, that he suspected the 

 tannin found in some peat-moors was produced during the imperfect 

 carbonization of the original vegetable substances : whether that is 

 really the case, or whether it has been afforded by heath or other 

 vegetables growing upon and near the peat, is, he says, still uncer- 

 tain, as he has never been able to detect any tanning substance in 

 peat, although he has examined a considerable number of varieties 

 of it. The great facility with which tannin is dissolved by water 

 causes it to be speedily extracted and drained from the substances 

 which, at first contained it : and that this facility of extraction ex- 

 tends to the most solid vegetable bodies, is shown by an experiment 

 made by our author on a piece of oak from the submerged forest at 

 Sutton, on the coast of Lincolnshire, described in the Phil. Trans, 

 for the year 1799. This oak, by decoction, afforded extractive matter, 

 but no traces of tannin could be perceived ; yet, by incineration, it 

 even afforded potash. 



Peat, however, although it does not contain tannin, is, by the im- 

 perfect carbonization it has undergone, rendered capable of being 

 converted, by treatment with nitric acid, into the artificial tanning 

 substance, in the manner already mentioned with respect to roasted 

 ligneous bodies. 



In the following section of his paper, Mr. Hatchett compares the 

 effect of the acetic, sulphuric, and nitric acids, upon resinous sub- 

 stances. The first of these he considers as the solvent of such sub- 

 stances, as it dissolves them speedily, without producing any apparent 

 subsequent change in their natural properties ; so that, by proper 

 precipitants, they may be separated from that acid in an unaltered 

 state. Sulphuric acid immediately dissolves resinous substances ; 

 but the moment the solution is complete, progressive alterations ap- 

 pear to take place in the dissolved substance, coal being the ultimate 

 product. 



The effects of nitric acid seem to be the reverse of those of 

 the sulphuric ; for by nitric acid the resins are converted into a 

 brittle porous substance, then into a soluble product intermediate 

 between extractive matter and resin, which product is converted 

 into the first variety of the tanning substance ; beyond which our 

 author has not been able to effect any change. A table of the quan- 

 tity of coal remaining after the treatment of various resinous sub- 

 stances with sulphuric acid is now given; respecting which we shall 



