U4 Mr. Hatchett’s Experiments on a Substance, 
at length total destruction. These effects are produced at 
different periods, according to the substance which may be 
the subject of the experiment, and therefore it is impossible 
at present to state the utmost quantity of the tanning sub- 
stance which, under equal circumstances, may be obtained 
from each of the resins, balsams, &c. 
The tanning substance appears to be always the same, 
whether obtained from turpentine, or common resin, or from 
the balsams, or from asa foetida, or camphor, or indeed from 
any of the bodies which have been enumerated ; its effects on 
the different reagents are similar ; by the addition of a small 
portion of nitric acid, and subsequent evaporation, it is con- 
verted into that which I have called the first variety ; or if 
digested with sulphuric acid, it is speedily destroyed, and 
becomes mere coal. In the latter case, therefore, the same 
agent which at first produced it becomes at length the cause 
of its destruction, and thus we find, that although a taming 
substance may be obtained from resinous and other bodies by 
means of sulphuric and by nitric acid, yet in the former case 
the product is variable, and is formed at or about the mean 
period of the operation, whilst the latter is an ultimate and 
invariable effect, beyond which, no apparent change can be 
produced by any continuation of the process.* 
§ III- 
I have already stated, that caoutchouc,, and elastic bitumen, 
were only superficially acted upon when digested for a very 
* In the former Papers upon this subject I have observed, that the tanning sub- 
stance produced by sulphuric acid, is very inferior in energy tq that, which is formed 
by nitric acid. 
