MINERALOGY, 
140 
SECT. CXLIIL 
Observations on Salts. 
The perfecl knowledge of thefe bodies muft be 
had from chemical books and praftical chemiftry, 
being almoft the chief fubjefl of that fcience. 
From thence we like wife learn why the acids are 
coniidered as falts, though a certain figure nei- 
ther is found, nor can reafonably be expedled in 
them. We are farther taught, that the angular 
figure, which is fuppofed to be eflential to falts, 
and by its varieties to mark out their different 
fpecies, depends on an alcali, earth, and metals, 
united with more or lefs water : for elfe, if this 
was not fo, the criftal of alum and vitriol ought 
to be of the fame figure, no nitrum aibicum would 
exift, nor could any criftallifation happen in fuch 
cafes, where the acids necefiarily muft be parted 
(Sed:. xi.). 
Salts are contained in all the three kingdoms of 
nature^ and as it is not yet known how the changes 
happen, and how far the varieties depend on one 
another, we cannot attribute to the mineral 
kingdom any other falts than thofe which are 
found truly changed in the earth. 
The ufe of the falts in medicine and in com- 
mon life is fo great, that it would require a fepa- 
rate treatife, if it were to be fully clifcuffed. Mean 
while, every one who applies himfelt to the ftudy 
of mineralogy, in order to learn the ufe to which 
the mineral bodies can be employed in commmn 
life, I mean in particular mines, muft endeavour 
to difcover where falts may be found, and how 
they muft be prepared, fo as to be beft fit for ufe. 
But the preparation of falts is not the fubjed of 
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