a 
PHYSICAL ann LITERARY. 237 
air, which muft proceed from its being 
incapable of union with fixed air and 
with the fedative falt at the fame time: . 
Whence it follows, that, were we to mix 
the fedative falt with an alkali faturated 
with air, the air would immediately be 
expelled, or the two falts in joining would 
produce anveffervefcence. This I found 
to be really the cafe upon making thetrial, 
by mixing a fmall quantity of the feda- 
tive falt with an equal quantity of each 
of the three alkalis, rubbing the mixtures 
wellin a mortar, and adding a little wa- 
ter. It is however proper in this place to 
obferve, that, if the experiments be made 
in a different manner, they are attended 
with a fingular circumftance. Ifa fmall 
quantity of the fedative falt be thrown 
into a large proportion of a diflolved fix- 
ed alkali, the fedative falt gradually dif 
appears, and is united to the alkali with- 
out any effervefcence; but, if the addition 
be repeated feveral times, it will at laft be 
accompanied with a brifk effervefcence, 
which will become more and more remark- 
able, 
