Chap. 2.] Hbw Oxygen Gas may be obtained. 373 



acids upon a variety of mineral and metallic fub- 

 ftances. 



In a fmall phial AB (Plate XXIX. Fig. i.) to 

 the mouth of which is fixed a bent tube C D, put an 

 ounce of the oxid of mercury, or hydrargyrus calci- 

 natm ; put it to heat over the chaffing difli R; and 

 after the atmofpheric air, which rilled the phial, is etf- 

 haufted, place the extremity D of the bent tube under 

 a long narrow glafs verTd (Fig. 2.) filled with the- 

 fluid in. the pneumatic apparatus or tub (Fig. 3.) and 

 place this w-Tel upon the board E F above the aper- 

 ture c or d *. 



As the mercury revives and becomes liquid, a com* 

 preflible, elaftic, tranfparent fluid may be obferved 

 to difengage itfclf, and pafs into that narrow glafs vef- 

 fel ; this is air of the pureft kind that we are able to 

 procure, namely, vital air or oxygen gas. 



This kind of air may alfo be obtained by the fame 

 procefs, from the native oxid or calx of manganefe, or 

 from minium or red lead, which, it is well known, is an 

 oxid of lead, or lead united with oxygen. 



The better to underftand thefe effects it mud be 

 recollected, as was obferved in the beginning of this 

 chapter, that this fluid is not found in thefe fubftances 

 in an entire Hate; they only contain the bafis of ir a 

 which is the oxygen \ for metals neither calcine nor 

 burn but in confequence of their combination with 

 oxygen, which by that means becomes folid, and joins 

 its weight with theirs. This oxygen is then expelled 

 by the heat or caloric, which, combining with it, caufes 

 it to pafs into the ftate of an elaftic fluid during this 

 procefs, the metal, lofmg the oxygen which had re- 

 duced it to the ftate of an oxid or calx, aflurfies its 



Traite Elem. de Phyf. torn, ii. p. 2 j., 



B b 3 metallic 



