222 Mr. Hatchett on an artificial tanning Substance. 
5. That of the coal afforded it in great abundance. 
Hence it appears, that these different modifications of tur- 
pentine yielded the tanning substance only in proportion to 
the quantity of their original carbon, which, by oxidizement, 
had been progressively converted into coal.* 
Other substances, when reduced into coal in the humid way, 
were in like manner formed into the tanning substance by nitric 
acid. In fact I found this to be the constant result, and amongst 
the many substances which were examined, I shall mention 
various kinds of wood, copal, amber, and wax, all of which, 
when reduced to coal by sulphuric acid, yielded similar pro- 
ducts, by subsequent treatment with nitric acid. 
But this substance may likewise be artificially produced 
without the help of nitric acid, although in a less proportion, 
as well as with some slight variations in its characteristic pro- 
perties ; for, as I have already observed, when any of the resins 
or gum resins (such as common resin, elemi, asa foetida, &c. ) 
have been long digested with sulphuric acid so as to assume 
the appearance and general characters of coal, if afterwards 
they are digested with alcohol, a portion is dissolved, and a dark 
brown solution is formed which by evaporation yields a mass 
soluble in water as well as in alcohol, and which precipitates 
gelatine, acetite of lead, and muriate of tin, but produces only 
a very slight effect on oxysulphate of iron. This substance, 
therefore, which may thus be separated by alcohol from the 
coal formed from resinous bodies by sulphuric acid, evidently 
contains some of the tanning matter, which has been produced 
during the carbonization of those substances. 
* Some late experiments have however convinced me that carbon need not be abso- 
lutely converted into coal in order to produce the artificial tanning substance; but this 
will be more fully explained in a subsequent Paper. 
