1 *7* J 
was at the dime time feparated from the acid ; but, as 
the earth was not able to abforb the whole of the 
fixed air, the remainder flew off in an elaffic form, 
and thereby produced an effervescence. 
Experiment XIII. 
The fame folution of volatile fal ammoniac made 
no precipitate, when mixed with a folution of Epfom 
fait ; though a mixture thereof with a little fpirit of 
fal ammoniac, made with lime, immediately precipi- 
tated the magnefia from the fame folution of Epfom 
fait; as it ought to do according to Dr. Black’s account 
of the affinity of magnefia and volatile alcalies to 
acids. This experiment is not fo eafily accounted for 
as the lafi; but I imagine, that the magnefia is really 
feparated from the acid by the volatile alcali; but that 
it is foluble in water, when united to fo great a pro- 
portion of fixed air, as is contained in a portion of 
volatile fal ammoniac, Sufficient to Saturate the fame 
quantity of acid. The reafon, why the mixture of 
the folution of volatile fal ammoniac, with the fpirits 
of fal ammoniac made with lime, precipitates the 
magnefia from the Epfom fait, is that, as the fpirits 
made with lime contain no fixed air, the mixture of 
thefe fpirits with the folution of volatile fal ammoniac 
contains lefs air in proportion to the quantity of acid 
which it can faturate, than the folution of volatile fal 
ammoniac by itfelf does. 
Volatile fal ammoniac requires a great deal of 
water to diffolve it, and the folution has not near fo 
ftrong a fmell as the fpirits of fid ammoniac mads 
with fixed alcali; the reafon of which is, that the 
latter contain much lefs fixed air. But volatile fal 
Z 2 ammo- 
