364 Dr. Hales. [Book V. 



ing the quantities both of the air, which was on fomc 

 occafions produced, and on other occafions abforbed, 

 by different fubftances. Thefe experiments deferve 

 the attention of every philofopher, and for accuracy or 

 ingenuity have never been exceeded *. 



Among other circumftances, which were particu- 

 larly remarked by Dr. Hales, was the great quantity of 

 air contained in the acidulated mineral waters, and to 

 this air he fufpected they were indebted for their fpark- 

 ]ing and brightnefs, and fome other of their peculiar 

 qualities. In obferving the abforption of air by bodies 

 in combuftion, he faw that this abforption had its li- 

 mits : he remarked alfo, in fome cafes, the alternate 

 production and abforption of air, as for inftance in re- 

 fpect to the air which he produced from the burning 

 of nitre, which air, he obferved, was very foon di- 

 minifhed in bulk, though he did not perceive that 

 the abforption was owing to the water, which he 

 always ufed in his experiments. The production 

 of an air capable of inflammation from the diftilla- 

 tion of certain fubftances did not efcape his obferva- 

 tionj and he has advanced, that the augmentation 

 of weight in the metallic calces was in fome de- 

 gree owing to the air which they imbibed. That the 

 phofphorus of Homberg diminifhes the air in which 

 it is burned i that nitre cannot explode in vacuo ; and 

 that air is in general neceflary to the cryftallization of 

 falts, are among the fads which are noticed by this 

 philofopher. 



From the uncertainty, however, of Dr. Hales and 

 his predeceftbrs, with rrgard to fcveral material cir- 

 cumftances, of which they appear to have had fome 

 cafual glimpfes, and from their total ignorance of others* 



* See Hales's Vegetable Statics, pajjim. 



the 



