190 An Analysis of two Mineral 
to it been black. Very little can be deduced with 
certainty from these trials, except the presence of a 
little sulphuric acid. It seemed of consequence to 
determine, whether this is generated in the process ; 
or is accidental, from the sulphuric acid which was 
used to extricate the gas. 
2. To determine this point, I repeated the expe- 
riment, using the muriatic acid to generate the gas, 
instead of the sulphuric. In this case, the liquor (as 
Bergman has said) is not at all rendered turbid by 
ptussiat of potash; neither does the muriat of barytes 
precipitate any thing; the precipitate by pure potash 
is now white, but as minute as before; nitrat of sil- 
ver makes a yellow cloud both before and after boil- 
ing; infusion of galls strikes a yellow tinge. Hence 
it is clear, that hepatic gas, when produced by sul- 
phuric acid, carries with it a little of the acid which 
cannot be separated by passing it through water. It 
seems probable also, that a little muriatic acid is car- 
ried up in like manner, when this is used to extricate 
the hepatic gas. We may farther conclude that though 
the remark of Bergman (on the effect of the prussiat 
of potash) is true; the remark which accompanies it 
(on the colour produced by infusion of galls) is er- 
roneous. A purple colour is always, I believe, oc- 
casioned by extraneous acid; in which case, the. 
prussiat of potash is also precipitated. From the 
same facts, we are enabled to detect another error 
also, into which the same great man has been be- 
