Mr. Hatchett on an artificial tanning Substance. 221 
The effects produced by sulphuric acid upon turpentine and 
resin are manifestly caused by the union of the two constituent 
principles of the latter ( namely, hydrogen and carbon ) with 
part of the oxygen of the former, so that sulphureous acid, 
water, and coal are produced. I therefore availed myself of 
this process, by which coal could be progressively formed 
whilst the original substance was gradually decomposed, to 
make the following experiment. 
A quantity of common turpentine was treated with sulphuric 
acid in the way which has been described, and different por- 
tions of the solution being poured at different periods into 
water whilst the remainder was digested during several days, 
I thus obtained from the same original substance, yellow 
resin, brown resin, black resin, and coal. I then digested 
a portion of each of these, as well as some of the turpentine, in 
separate vessels with nitric acid until they were completely 
dissolved, and afterwards reduced them to dryness. The 
different residua varied in colour from yellow to dark brown, 
corresponding to the substances which had been employed. 
These were then dissolved in distilled water, and were exa- 
mined by solution of isinglass and other reagents. 
1. The solution of the residuum of turpentine was pale 
straw colour, and did not precipitate gelatine. 
2. That of yellow resin resembled the former in every respect. 
3. That of the brown resin was of a deeper yellow, but in 
other particulars resembled the above. 
4. That of the black resin on the contrary yielded a consi- 
derable portion of the tanning substance, — and 
distillation in a small glass retort placed over an open charcoal fire, the residuum of 
coal only amounted to | of a grain. 
