On phlogiston. 471 



obtained, is always in proportion to the coal contained in 

 iron. 



Bar iron contains a fmall quantity of coal, compared to 

 call iron, and by heating caft iron in oxygenous gas, much 

 more carbonic acid may be produced, than from bar iron. 



Dr. Prieftley fays, that the plumbago contained in iron, 

 could not be difengaged from it in this procefs, and if it 

 could, it would not yield the hundredth part of the fixed 

 air that is produced. 



The charcoal contained in plumbago, can certainly be 

 difengaged from it with the greateft eafe, for every par- 

 ticle of it, is expofed to a high degree of heat in oxygen- 

 ous gas. 



Two other arguments ufed by the Dodor, to prove 

 that fixed air may be procured without charcoal, are : 



That a great quantity of this kind of air, may be pro- 

 duced from heating a mixture of iron filings and red pre- 

 cipitate, or iron filings and turbith mineral. 



Five attempts were made to obtain carbonic acid gat:, 

 by expofmg from half an ounce to an ounce of red preci- 

 pitate, mixed with an ounce and two ounces, of the filings 

 of bar iron, filed for the purpofe, to a red heat, in a clean 

 iron tube, without fuccefs. The mercury of the precipi- 

 tate was revived, no air was obtained, and the iron was 

 reduced to a calx. 



Mixing five drachms of the fame kind of filings, and 

 as much turbith mineral, and expoiing the whole to a red 

 heat, the fame refult happened. 



Having then recourfe to caft iron, half an ounce of red 

 precipitate was mixed with an ounce of the borings of: 

 cannon, and thirty-two ounce meafures ot air were obtain- 

 ed, eleven of which were fixed, and twenty-one intiani- 

 mable. 



One ounce of this iron, without any red precipitate, ex- 

 pofed to a red heat, gave forty ounce meafure-. of air, 

 eight of which were fixed and thirty-two inilamniable. 



One 



