468 Mr. Henry on the Natural Hiftory , i£c. 
It is very probable that the Magnefia, ufed 
in the experiments of Meffrs. Bergman and 
Morveau, was pure, as the former recommends, 
and the latter actually employed, the Volatile 
Alkali, to effeCt the precipitation of the earth. 
The difference, therefore, between their experi¬ 
ments and that of M. Macquer, mod probably 
depended on the communication of fome portion 
of Siliceous or Argillaceous liarth, from the 
crucible in which they were made. Whereas 
M. Macquer’s experiments, being made in a 
metallic box, and the heat directed immediately 
to the Magnefia, no tendency to vitrification 
would appear. 
In regard to the difference between the 
Magnefia, which was firft expofed to Mr. 
Parker’s lens, and my own, I can only fpeak 
from conjecture. I have been particularly care¬ 
ful to have my Alkaline Lixivium, which is, 
a folution of the ftneft pot afh, perfectly purified : 
and have frequently obferved, that after it has 
been freed from all Neutral Salts, and from all 
the earthy matter, that the filter could feparate, 
the folution, on long {landing, has become 
again turbid, and depofited a copious white 
fediment. Bergman, who deferibes a fimilar 
fediment declares it to be Siliceous Larth, 
that had been held in folution by the Alkali, 
and is precipitated by the fixed air, attracted by 
the fait. This faCt is adduced by him, as a 
proof 
