238 ESSAYS anv OBSERVATIONS. | 
able, until the alkali be entirely facurated” 
with the fedative fait. 
THIS phenomenon may be explained by 
confidering the fixed alkalis as not per- 
fectly faturated with air: And the fuppo- 
fition will appear very reafonable, when 
we recollect, that thofe falts are never pro- 
duced without a confiderable degree of 
heat, which may eafily be imagined to’: 
diffipate a {mall portion of fo volatile a 
body as air. Now, if a fmall quantity 
of the fedative falt be thrown into an al- 
kaline liquor, as it is very flowly diflolved 
by water, its particles are very gradually 
mixed with the atoms of the alkali. 
They are moft ftrongly attracted by fuch' 
of thefe atoms as are deftitute of air, and 
therefore join with them without produ- 
cing an effervefcence; or, if they expel a 
fmall quantity of air from fome of the falt, 
this air is at the fame time abforbed by 
fuch of the contiguous particles as are 
deftitute of it, and no eftervefcence ap= 
pears until that part of the alkali, which 
was in a cauftic form or deftitate of air, 
be nearly faturated with the fedative fale. 
But 
