3y3 Properties of Oxygen Gas. [BookV. 



On introducing a lighted candle into pure or dephlo- 

 gifticated air, the flame becomes larger and brighter ; 

 and whenever the air is very pure, the candle burns 

 with a crackling noife, as if the air contained fome 

 combuftible matter, while the tallow or wax wades, 

 or is conformed, incredibly raft. When after this pro- 

 cefs the candle is extinguifhed, it will be found that 

 two-thirds of the bulk of air employed will be con- 

 verted into fixed air. When the fixed air is taken up 

 by lime water or cauftic alkali, the fmall remainder 

 will be as pure as before. 



In common procefles, not more than one-tenth of 

 the air employed is converted into fixed air. It is 

 probable, that in thefe experiments fome diminution in, 

 the volume of air muft take place, from the fuperior 

 gravity of fixed air, and the confequent condenfation 

 of the other, 



If live coals are introduced into a veflel filled with 

 dephlogifticated air, it will be found to be diminifhed 

 one-fourth of its quantity. When this experiment is 

 repeated with fulphur, the flame will become larger 

 and more vivid than in common air, and three-fourths 

 of the quantity will be loft. If a piece of phofphorus, 

 is put into a feven ounce meafure of this kind of air, 

 the mouth of the bottle being corked, and the phof- 

 phorus being fet on fire within it, the phial will break 

 in pieces, as fopn as the flame is extinguiihed., by the 

 prerTure of the external air. 



The purity of vital air is afcertained by its degree 

 of diminution with nitrous air, or gas obtained from 

 nitrous acid, and this proccfs is to be confidered as a. 

 jpecies of combuftion, efpecially as a cpnfiderable de- 

 gree of heat is generated by it. Very great differences, 

 however, are perceived in this refpecl } and according 

 to the quantity of diminution, the air is faid to be two, 



three, 



