220 Mr. Hatchett on an artificial tanning Substance. 
general, and may be referred to those attendant on etherifica- 
tion, for my intention here is only to notice, in a concise 
manner, such as immediately tend to elucidate the subject of 
this Paper. 
When concentrated sulphuric acid is poured on the common 
turpentine of the shops, it almost immediately dissolves it like 
the solid resins ; and if a portion of this solution be poured into 
cold water, the turpentine is precipitated in the solid brittle 
state of common yellow resin. But if a second portion of the 
same solution, after the lapse of an hour or more, be in like 
manner poured into cold water, the resin thus formed is not 
yellow but dark brown ; and if four or five hours are suffered 
to elapse before a third portion is poured into water, the resin 
is found to be completely black. After this, supposing the 
digestion to be carried on during several days, or until there 
is no longer any production of sulphureous gas, the turpentine 
or resin will be found converted into a black porous coal, 
which, if the operation has been properly conducted, does not 
contain any resin, although a substance may frequently be 
separated by digestion in alcohol, which I shall soon have 
occasion to notice. 
When common resin was thus treated, I obtained about 43 
per cent, of the coal, which, after being exposed to a red heat 
in a loosely covered platina crucible, still amounted to 30 per 
cent, and by the slowness of its combustion and other circum- 
stances which need not here be related, approached very 
nearly to the characters of some of the mineral coals.* 
9 The difference of the quantity of carbon, which may be obtained in the state of 
coal from resinous substances by the humid and by the dry way, is very considerable! 
we may take common resin as an example, for when 100 grains were exposed to simple 
