394 General Properties of [Book V. 



fhaft of the mine to the afh-pit of a furnace, when 

 the infiammablc vapour will be conftantly attracted to 

 feed the fire. 



Dr. Prieftley has fufftciently proved by experi- 

 ments, that there is no acid contained in inflammable 

 air. He alfo afierts that charcoal, by the heat of a 

 burning lens, may be almoft totally converted into 

 this .kind of air, but that fomc moifture is neceflary 

 in the procefs. The neceflity of moifture, how- 

 ever, to the fuccefs of this experiment, iufficiently 

 evinces the fallacy of the conclufion which has been 

 drawn from it. Perfectly pure charcoal, abftradted 

 from every other body, is indeftrudtible by heat. 

 Where, however, there is moifture there is water. 

 In this cafe the oxygen of the water is attracted by 

 the carbon, forming with it carbonic acid, and the 

 hydrogen, the other constituent part of water, rifes 

 to the top of the receiver. Pure hydrogen gas 

 is the lighted of all elailic fluids, its fpecific gravity 

 is to that of common air as 8,04 is to 100,00*. 



The moft remarkable properties of this gas are, 

 ift. Its great inflammability, which ariles from its 

 propenfity to unite with oxygen and form water, 

 adly. Its extraordinary levity, as already noticed. 

 3clly. Metals are very eafily revived or reduced from 

 a calx or oxyd to the metalic ftate when heated in 

 a receiver filled with this air. This alfo arifes from 

 its attraction for oxygen, which in this cafe is ex- 

 pelled from the calx, and, uniting with the hydrogen 

 in the receiver, leaves the metal pure, and in its na- 

 tural ftate. 4thly. Plants vegetate in this fluid with- 

 out impairing its inflammability, fthly. Water will 

 imbibe about one-thirteenth of its bulk of this gas,, 



* See Briffor, torn, ii, p. 77. 



which 



