21 6 Mr. Hatchett on an artificial tanning Substance . 
to these solutions only deepened the colour, but, after some 
hours, rendered them turbid. 
g. Glue or isinglass was immediately precipitated by these 
solutions from water, and the precipitates were more or less 
brown according to the strength of the solutions. The pre- 
cipitates were also insoluble in cold and in boiling water, so 
that in their essential properties they proved similar to those 
formed by the varieties of tannin hitherto known, with the 
difference, that this factitious substance appeared to be exempt 
from gallic acid, and mucilage, which commonly accompany 
the varieties of tannin, and which occasion modifications in the 
colour and appearance of some of their precipitates. 
Having thus had the satisfaction to discover that a product 
resembling tannin could be formed by such a simple method, 
not only from vegetable but also from mineral coal, I was 
induced to examine how far the same might be extended to 
animal coal, and I therefore reduced a portion of isinglass 
to that state in a close vessel, and having rubbed it into fine 
powder, I digested it with nitric acid in the manner which 
has been described. At first the acid did not appear to act 
upon it, but at length it was slowly dissolved excepting a small 
quantity, which however was in every respect unchanged; 
and here we may remark, that as animal coal is incinerated 
with much more difficulty than vegetable coal or charcoal, so 
was the same difference to be observed, when oxygen was 
presented to these bodies in the humid way. 
The solution resembled those which have been described, 
excepting, that the brown colour was more intense. It was 
evaporated to dryness, and was then dissolved in distilled 
