Analyfis of the Air. 187 
of vegetables are fee to cryftallize, it is 
needful to take off the skin or Pellicle, 
which covers the liquor, before the falts 
will fhoot well. 
We fee from the great quantity of air, 
which is found in falts, of what ufe it is 
j in their cryftallization and formation 5 and 
particularly how needfary it is in making 
falt-petre from the mixture of fait of tartar 
i and fpiritof nitre. Forlince by Experiment 
I 72 and 73, a great deal of air flies away, in 
the making of Sal Tartar, either from nitre 
and tartar, or from tartar alone ; it muft 
needs be necefiary, in order to the forming 
of nitre from the mixture of Sal Tartar and 
fpirit of nitre, that more air Ihould be in- 
corporated with it, than is contained either 
in the Sal Tartar or fpirit of nitre. 
Experiment LXXV. 
Near half a cubick inch of compound A- 
qua-fortis, which bubbled and made a con- 
fiderable expanfion in diftillation was foon 
diftilled off : as it cooled the expanfion a- 
bated very fail, and a little air was abforb- 
ed. Whence it is evident that the air ge- 
nerated by the diftillation of nitre, did not 
arife from the volatUe fpirituous particles. 
2 Hence 
