the Nature offome Mineral Subjtances. 6 > ; 
the three forts of horn 
were as colourlefs as w 
copper. 
iilver in fpirit of liart’s-horn 
ater; a proof they contain no 
To give a proof of the exiftence of the acid of fait in 
the horn iilver, I took four grains of the cubical cry Hals 
obtained in the leventh, eighth, and ninth experiments, 
and having put them into feparate wine-glades, poured 
a little oil of vitriol on each, which made them all boil up, 
effervefce, and fend forth copious fumes of acid of fait, 
juft as the like quantity of fea-falt would have done. 
In order to give alfo a convincing proof, that the horn 
Iilver contained acid of vitriol, I availed myfelf of M. 
margraf’s difcovery, who fays, that a folution of cal- 
careous earth in acid of nitre is precipitated by a folution 
of tartar of vitriol; for the acid of vitriol forfakes its 
alkaly to unite, and form a felenite with the calcareous 
earth. I therefore diilolved twelve grains of tartar of 
vitriol in diftilled water, and having filtered the folution,. 
I added to it a fufficient quantity of a folution of chalk 
in acid of nitre, which caufed a precipitation ; this pre- 
cipitate, being edulcorated and dried, weighed feven 
grains : this ferved as a comparative experiment. It is- 
probable, from the fmall quantity of this precipitate, that 
the whole of the tartar of vitriol was not decornpofed.. 
It fhews, however, that feven grains of this precipitate 
require twelve grains of tartar of vitriol to their for- 
mation. 
The neutral fait of the feventh experiment, treated in 
:he like manner, produced eight grains of felenite; that 
of 
