Vital Air In the Atmofpherc, 255 



by mcafurlng the refiduum of the quantity of air employed, 

 the quantity which has difappeared, and which can be no- 

 thing but vital air, will be determined. During fume days 

 of the year 1787, in which the con)mon air experienced no 

 variation by the means of nitrous air, fince 100 parts of each 

 were uniformly reduced to 99 or co, I was defirous of 

 making a comparative trial of the fame common air by 

 means of iron and fiil[)hur, and I obferved that of 100 parts 

 of air there remained from 79 to. 81, and that, confecjuently, 

 from 19 to 21 hundredths had difappeared. On fimilar days 

 1 expofed 100 parts of atmofphcric air to liquid fulph'^ret, 

 and found that the air loft between 21 and 23 parts. From 

 this circumflance of always finding the relults of the laft 

 proof higher, I began to fufpedl that fulphuret, and a mix- 

 ture of iron and fulphur, ought not to be employed indifier* 

 cntly, but that the former ought to be preferred. AVhen I 

 recolle6led, indeed, the obfervations of Lavoilieron the fornix 

 ation of the vitriolic acid, and thofe of Dr. Prieftlev, that a 

 paltc of fulphur and fihngs of iron gave inHammable air in 

 certain circumftances; I knew that during the abforption of 

 vital air the latter unites itfelf with the ful]}hur, producing 

 by the combination fulphuric acid, Which, in exercifins; its 

 adlion on the iron, produces a little inflammable air, v\/hich 

 afcends to joi;i itfelf to the azotic gas remaining in the upper 

 part of the veflel after the operation ; and though there really 

 difappeared from 21 to 23 parts of vital air which enier into 

 the compofition of 100 parts of atmofpheric air, it feems that 

 only from 19 to 21 were really wanting; fince, befides the 

 077 or 0*79 of mephitic air, O'l or 02 parts of inflammable 

 gas united themfelves alfo, from which there refulted from 

 o*79 to o*8i. It appeared not only from the experiments of 

 common air, but from thofe alfo of another kind very fupe- 

 rior, fuch as that extra6led from the American agave, .that 

 a very fmall quantity more was diminiflicd by fulphuret than 

 by the mixture of iron and fulphur; fo thaft air, extracted 

 from that plant, with proper precautions, is fo pure that fofne- 

 times it is found free from every other aerial fubftance; and 

 is abforbed by the fulphuret without the refiduiin'. of a hun- 

 dredth part. 



Vrccf 



