jiddittonal Ohfervat'wns on Hydrocarhonatei. 209 



partly diffufed through the chalk in fmall metallic globules. The decompofition of the acid 

 in this experiment was very imperfeft, when compared with that in the former, owing no 

 doubt to the different affinities of the metals for oxigen. 



Although there could be no doubt, that in all thefe procefles with the carbonate of lime 

 and the metals, the carbonic acid muft have been dccompofed in its nafcent ftate, yet I 

 conceived that it might give ftill an additional fatisfaition to (liew, that the fame fubllancc 

 may be readily decompofed even when in the ftate of gas. This was accompliflied in two 

 ways. 



Into a ftralght iron retort with a cylindrical belly, a quantity of dry and very pure fand 

 was introduced, and above this a ftratum of chalk- which had been very carefully dried ; 

 more fand was then introduced, and rammed down, until it filled up no lefs than three 

 inches of the cavity above the chalk, and upon this was placed a quantity of very clean iron 

 filings, the whole occupying about two thirds of the belly* The retort was then fixed in 

 a furnace, and made red hot as foon as poffible ; the firft gas which came over was chiefly 

 carbonic acid ; the fecond portion amounting to a gallon, confifted of carbonic acid gas 

 one part, and gafeous oxide three parts ; the third portion being upwards of two gallons by 

 meafure, confifted of carbonic acid two parts, and gafeous oxide feven parts ; andthelaft" 

 portions examined, contained a fomewhat greater proportion of carbonic acid gas. The 

 gafeous oxide was found to be of the pureft kind. In this experiment the carbonic acid 

 was not brought into contaft with the iron In its nafcent ftate, but after it had aflumed its, 

 gafeous form, and pafled through a quantity of fand. The iron filings too being unmixed 

 with the chalk, fhewed evident marks of oxidation, a confidcrable portion of them being 

 converted into the ftate of grey oxide. 



The other method by which I decompofed this acid in its gafeous form, was by making 

 it pafs through a red hot iron tube filled with iron wires. In this experiment, a bladder, 

 mounted with a ftop cock, and containing a quantity of carbonic acid gas, was attached 

 to one end of the tube, fo as to be air tight at the joining ; the tube was then pafled through 

 a portable furnace, and an empty bladder mounted in the fame manner fixed to its other 

 extremity ; heat was then applied, to the middle of the tube until it became red, taking- 

 care at the fame time to keep its extremities cold, by means of wet cloths wrapped round 

 them. When the tube was fufficiently hot, the gas was made to pafs flowly through it 

 from the full bladder to the empty one, and then back again from the latter to the former. 

 This was repeated ten times, when a little of the gas left in one of the bladders was exa- 

 mined, which by means of the ftop cocks could be managed at pleafure. This gas was 

 found to confift of one part inflammable gas, and two parts carbonic acid ; the bladder 

 ■was then re-applied, and the gas forced backwards and. forwards ten times as before ; on 

 re-examination it was now found to confift of inflammable gas, and carbonic acid gas in the 

 proportion of 1 1 to 5 ; but by continuing the procefs a little longer, no lefs than three 

 fourths of the original carbonic acid gas was converted into an inflammable gas, and which 

 on examination was found to be the true gafeous oxide of carbon; the wires after tha 



Vol. V.-»September i8oi. Ec tube 



