366 Dr. Prufty. [Book ^ 



iron or zinc, afforded a particular fpecies of air, which 

 loft its clafticity by coming in contact with water. 



Dr. Prieftley commenced his philofophical career 

 byjbfne experiments upon fixable air; and the firft of 

 his communications to the public related to the im- 

 pregnating of water with this air, by means of chalk 

 and oil of vitriol, a method firft hinted by Dr. Brown- 

 riggof Whitehaven, and now commonly practifed irt 

 the imitations of the acidulated mineral waters* The 

 Doctor tried the power of fixnble air upon animal and 

 vegetable life, and found it fatal to both; and he made 

 fever.il other valuable experiments, the fubftance of 

 which will be related in the chapter on fixed air* 



The indefatigable mind of Dr. Prieftley was hot> 

 however, to be fatisfied with the inveftigation of a fmglc 

 object. He next turned his attention to the nature of 

 atmofpheric air. He obfcrved, after Dr. Hales, its 

 diminution by different procefTes, as. by combuftion, 

 &c. but differed as to the caufe. Dr. Hales fuppofed 

 the fpecific gravity of the air to be increafed ; but Dr* 

 Prieftley judged, that the denfer part of the air is pre* 

 cipitated, and that the remainder is actually made 

 lighter. The difcovery that the atmofpheric air is 

 purified by vegetation is alfo Dr. Prieftlcy's. 



On purfuing the experiments of Mr. Cavendifli on 

 inflammable air, the Doctor found that it was not only 

 producible from iron and zinc, but from every inflam- 

 mable iubftancc whatever. 



Dr. Prieftley difcovered the caufe that air, which 

 has been refpired, is fatal to animal life, to be, that it 

 becomes impregnated with fomething ftimulating to 

 the lungs, for they are affected in the fame manner ai 

 when expofcd to any other kind of noxious air. His 

 experiments on the means of reftoring falubrity to air 

 are highly interefting and entertaining, and afford a 



pleafing 



