Analyfis of the Air. i2i 



not Ihoot into fair cryftals of falt-petre, till 

 it had been long expofed to the open air, 

 whence he fufpected that the air contribut- 

 ed to that artificial produ&ion of falt-petre. 

 And fays, " whatever the air hath to do in 

 a this Experiment, we have known fuch 

 u 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. 30s. and VoL 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 neceffary it is in making 

 falt-petre from the mixture of fait of tartar 

 and fpirit of nitre. For fince by Experiment 

 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 mud 

 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, 



N 3 Ex- 



