304 ESSAYS anv OBSERVATIONS 
THERE is indeed another manner of part- 
ing the diffolved body from the folvent, which 
is fometimes, tho” lefs properly called pre- 
cipitation ; when, by drawing off part of 
the folvent liquor by evaporation or diftilla- 
tion, the diffolved body falls down gradual- 
ly in proportion to the quantity of the liquor 
watted. 
I fhall chiefly confider the firft or more 
proper precipitation, in which there is both 
greater variety, and more difficulty to account 
for the change. 
Remark 1. Avv precipitations do not hap- 
pen from the oppofition of an alcali to an acid ; 
but there are different means of precipitating 
different folutions. 
Ir is certain, from experience, that what- 
ever bodies are capable of being diflolved in 
any acid liquor, may be precipitated from it by 
an alcaline falt or liquor. On the other hand, 
any body that is diffolved in an alcaline li- 
quor may be parted from it by the addition 
of an acid. This then is a pretty general 
method of precipitating : however this op- 
pofition of acid and alcali is not the fole 
caufe of precipitation ; for many metals and 
metallic 
