the Nature of Jome Mineral Subjlances. 623 
the oil of tartar is owing to the phlogiftic fixed air 
oi the the minerals; but of this I tfiall treat more 
fully 111 another paper; and will now only add, that 
chalk,, diftilled per fe , with a ftrong fire, makes the oil of 
tartar in the receiver alfo cryftallize. I mult, however, 
own, that no cryftallization is obferved in the upper part 
of the receiver ; nor was it to be expedted, on confiderin^ 
the moilture which the chalk affords in diftillation. ** 
M. le sage fays, that the cryftallizations in the upper 
part of the receivers in his experiments were compofed 
ol cubic ciyftals ; but in all mine they were fpiculine. 
By the foregoing experiments it appears, that filver 
and quickfilver are the only fubftances which are mine- 
ralized by the acid of fait, and that they are alfo com- 
bined with acid of vitriol. 
Though the remit of my experiments has been very 
different from that of the fame fubftances examined by 
M. le sage, yet I have too high an opinion of him, and 
know him too well, to call his veracity in queftion. I am 
rather inclined to fufpedlthat this difference may proceed, 
from his having ufed oil of vitriol that contained acid of 
fait. Mr. holker, w ho prepares this acid in France, owned 
to me, that he had, in his firlf tryals, mixed fea fait in 
the preparing of it, with a view to increafe its quantity. 
Might not M. le s age have made his experiments with 
fuch an acid; and of confequence obtained acid of fait 
from the fubftances he tried. 
PR E- 
