296 Mr. Hatchett’s additional Experiments 
Lastly, when dissolved isinglass was added to the yellow 
solution of indigo, it immediately became very turbid, and a 
bright yellow substance was gradually deposited, and coated 
the sides of the glass jar with a tough elastic film, which was 
insoluble in boiling water, and possessed the characters of 
gelatine combined with tanning matter. 
By this experiment I therefore ascertained, that a variety 
of the artificial tanning substance could be formed without 
previously converting the vegetable body into coal ; and I have 
since discovered, that although indigo more readily yields this 
substance than most of the other vegetable bodies, yet in fact, 
very few of these can be regarded as exceptions, when sub- 
jected to repeated digestion and distillation with nitric acid. 
2. — A. In my former Paper I have stated, that common 
resin, when treated with nitric acid, yielded a pale yellow so- 
lution with water, which did not precipitate gelatine, and that 
it was requisite to develope part of the carbon in the state of 
coal by sulphuric acid, before any of the tanning substance 
could be produced ; but having again made some of these 
experiments, I repeated the abstraction of nitric acid several 
times, and then observed, that the solution of resin in water 
acted upon gelatine similar to the solution of indigo which has 
been described, and formed a tough yellow precipitate, which 
was insoluble in boiling water. 
With other reagents the effects were as follows. 
Sulphate of iron, after 12 hours, formed a slight yellow 
precipitate. 
Nitrate of lime did not produce any effect. 
Muriate of tin, after 12 hours, afforded a pale brown preci- 
pitate. 
