ATMOSPHERICAL AIR. 3 



period of greateft diminution, an increafe of the quanti- 

 ty, and that it is then found to contain a mixture ot in- 

 flammable air. 



That fomething is really emitted from the iron filings 

 and fulphur, when it is in a llate of diminilhing air is 

 evident from the ftrong and o'Scu'CiYe.fmell which at that 

 time this mixture has. Flowers alio, and efpecially 

 thofe which have the ftrongeft fmell, I have obfcrved 

 to phlogifticate air. Moreover, the iron filings and 

 fulphur when nearly dry, emit a vifible denfe vapour, 

 which appears by its fmell to be vitriolic acid air, which 

 I have obferved to have the power of diminifliing and 

 phlogifticating air ; owing no doubt, in part to its im- 

 bibing the dephlogifticated part of it, and with it form- 

 ing common vitriolic acid ; but at the fame time part of 

 its phlogifton may unite with another part of the dephlo- 

 gifticated air, and with it form phlogifticated air. 



Iron filings and fulphur, as well as phofphorus, and 

 moft of the other fubftances which have been gene- 

 rally ufed for the purpofe of phlogifticating atmofpherical 

 air, do likewife imbibe the dephlogifticated air contained 

 in it, and thereby gain an addition of as much weight as 

 the air has loft. JBut this is not the cafe with black bones 

 heated in air, which by this means become white ; 

 and as nothing in them is volatile, except that which 

 conftitutes their blacknefs, I thought they would be a 

 very convenient fubftance with which to make thefe ex- 

 periments. 



Thefe bones gained no addition of weight in the pro- 

 cefs, and when they are ufed, the diminution of the air 

 is by no means fo great as in the other cafes, though the 

 air that is left is completely phlogifticated. This is pro- 

 bably in confequence of the fixed air (formed by the 

 union of the dephlogifticated air with the phlogifton 

 emitted from the bones) not being readily imbibed by 

 A 2 the 



