Analyfts of the Air. i 8 r 
not (hoot into fair cryftals of falt-petrc, till 
it had been long expofed to the open air, 
whence he fufpeded that the air contribut- 
ed to that artificial produflion of falt-petrc. 
And fays, “ whatever the air hath to do in 
this Experiment, we have known fuch 
changes made in fome faline concretes, 
chiefly by the help of the open air, as 
very few would be apt to imagine/' Vol. 
I. p. 302. andVoL 3 . p. 80. 
We fee from the great quantity of air, 
which is found in falts, of what ufe it is 
in their cryftalization and formation, and 
particularly how necelTary it is in making 
falt-pctre from the mixture of fait of tartar 
and fpirit of nitre. For lince by Experiment 
72 and 73> a great deal of air flics away, in 
the making of 4^/^/ either from nitre 
and tartar, or from tartar alone : It muft 
needs be neceffary, in order to the forming 
of nitre from the mixture of Sal Tartar and 
fpirit of nitre, that more air fhould be in- 
corporated with it, than is contained either 
in the Sal Tartar or fpirit of nitre. 
K 5 
