46' ON TH * DOCTRINE OF PHLOGISTON. 



in the middle with iron wire. Bladders rilled with this gas 

 were attached, by ftopcocks, to the extremities of the tube. 

 After the middle of the tube, placed in a furnace, had been 

 made red hot, the gas was repeatedly pafled, and very flowly, 

 from one bladder to the other. During this pafTage it was ex- 

 pofed to a very extenlive furface of red-hot iron ; and in one 

 of the laft experiments made in this manner, after forcing the 

 gas through the tube backwards and forwards 30 times, four 

 parts in five of the carbonic acid gas was converted into ga- 

 feous oxide: the gas upon the whole was a little diminifhed. 

 The iron- wires, after the operation, were covered with the 

 fame mining cruft as if the fteam of water had pafled over 

 them ; and in fact they were oxidated or calcined to a certain 

 extent, in confequence of feizing from the carbonic acid a 

 proportion of its oxigen fufficient to convert it into the inter- 

 mediate ftate of an oxide *. 



Dr. P. could not The method by which Dr. Prieftley attempted to decom- 



decompofecar- p f e t b e carbonic acid gas, by heating pieces of iron with a 



bonic acid by the j . ,,^11,^ 



burning glafs * en s placed in it, could not pombly have iucceeded, at leaft to 



with iron, be- anv f en fible degree ; for the heated air when left at liberty to 

 of ignited furface afcend, would not remain in contact with it, nor even near it, 

 was inefficient, for a moment : thus every portion of air, being unconfined, 

 would expand prodigioufly, fo that very little of it could come 

 or remain in contact with the heated metal. In the experiment 

 above related, the gas was computed to pafs feveral times over 

 a furface of red-hot iron of fome extent ; yet, notwithstanding 

 this, a considerable time was required to produce any remark- 

 able decompofition in the acid ; a circumftance which proves 

 that, in the method employed by Dr. Prieftley, no fenfible de- 

 Simpler method compofition could have been produced. There is likewife, 

 of decompofing j n mv fecond Eflay, another method itill Ampler for decom- 

 pofing the carbonic acid in its gafeous ftate f. All the oxid- 

 ible metals are, when raifed to a high temperature, capable of 

 decompofing it more or lefs; but zinc is by far the raoft 

 powerful, owing no doubt to its greater affinity to oxigen. 

 Though mere Dr. Prieftley afks, if, in the experiment with the finery cinder 

 heat does not and charcoal, the oxigen to form the carbonic acid fliould come 

 from finwyVm- ^ rom tne ca * x > now ' s ** to ^ ex P e ^ ec ^* as neat alone will not 



and'the attrac- * ^ or l ^ e particulars of this experiment, and the mode of con- 

 tion of charcoal dueling it, fee this Journal, quarto f. No. 55. p. 209. 

 »»yi t No. 55. p. 209. 



do 



