C J 59 ] 



from the calx may be promoted by that (mall quan- 

 tity of oil of vitriol, which I am informed is con- 

 tained in chalk, if not in lime-flone alio. But it is 

 an objection to this hypothecs, that the inflammable 

 air produced in this manner burns blue, and not at 

 all like that which is produced from iron, or any other 

 metal, by means of an acid. It has alfo the fmell 

 of that kind of inflammable air which is produced 

 from vegetable fubftances. Befides, oil of vitriol 

 without water, will not difTolveiron ; nor can inflam- 

 mable air be got from it, unlefs the acid be consi- 

 derably diluted ; and when I mixed brimftone with 

 the chalk, neither the quality nor the quantity of the 

 air was changed by it. Indeed no air, or permanently 

 elaftic vapour, can be got from brimftone, or any 

 oil. 



In the method in which I generally made the 

 fixed air, and indeed always, unlefs the contrary be 

 particularly mentioned, viz. by diluted oil of vitriol 

 and chalk, I found by experiment that it was as pure 

 as Mr. Cavendifh made it. For after it had pafTed 

 through a large body of water in fmall bubbles, flill 

 ._l_ or ~ part only was not abforbed by water. In 

 order to try this as expeditioufly as polTible, I kept 

 pouring the air from one glafs veflel- into another, 

 immerled in a quantity of cold water, in which 

 manner I found by experience, that almoft any 

 quantity may be reduced as far as pofiible in little 

 more than a quarter of an hour. 



At the fame time that I was trying the purity of 

 my fixed air, I had the curiofity to endeavour to 

 alcertain whether that part of it which is not mif- 

 fcible in water, be equally diffufed through the whole 



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