254 Mr. Hatchett’s additional Experiments 
experiments, by which I obtained a variety of the artificial tan- 
ning substance in a way different from that which has been 
related, and with which I was unacquainted when my former 
paper was written. 
§ iv. 
.1 made several unsuccessful attempts to form the artificial 
substance by means of oxymuriatic acid, and it therefore ap- 
peared certain, that although a variety of the tanning matter 
could be produced by the action of sulphuric acid on resinous 
substances, yet the most effective agent was nitric acid, which 
readily formed it when applied to any sort of coal. 
But I nevertheless suspected, that possibly this substance, or 
something similar to it, might be produced without absolutely 
converting vegetable bodies into coal ; for it seemed, as I have 
observed in my former paper, that this only served to separate 
the carbon in a great measure from the other elementary prin- 
ciples ( excepting oxygen ) which were combined with it in the 
original substance, and thus to expose it more completely to the 
effects of the nitric acid, as well as to prevent the formation of 
the various acid products, which are so constantly afforded by 
the organized substances when thus treated. At first I had 
some thoughts of employing touchwood in this experiment, but 
not being able immediately to procure any, it occurred to me, 
that indigo might probably answer the purpose ; for from some 
experiments made by myself, as well as from those described 
by Bergman,* I well knew that the proportion of carbon in 
this substance is very considerable. The following experiment 
was therefore made. 
* Analysis Cbemica Pigmenti Indici. Opuscula Be sg, Tom. V. p. 36. 
