21* Jlddiiknal Qh/ervatkttt on Hydnearlottaiet. 



tube had cooled were examined, and found covered in feveral places with a beautiful fhlning- 

 crult of grey oxide, which readily crumbled and fell ofFon bending the wire. The car- 

 bonic acid employed in this experiment was procured from carbonate of foda by means o£ 

 the dilute fulphuric acid, and amounted to 64 ounce meafures ; during the procefs very 

 little diminution of increafe of bulk could be perceived, which is readily accounted for» 

 from the very trifling diminution the gafeous oxide undergoes when converted into carbonic 

 acid gas. 



From the various fa£l» w^hich have been now enumerated, added to thofe already 

 known, there can no longer remain any doubt, that the carbonic acid, under certain ele- 

 vations of temperature, may be readily decompofed by any fixed fubftance, having a con- 

 fidcrable affinity for oxigen ; and that with regard to the metals, thofe fuccecd the beft 

 which have the greateft attradlion for acids or oxigen, as is remarkably exemplified in zinc. 

 Upon the whole then I think we may conclude, that ther6 are but two diftindt combina- 

 tions of carbon and oxigen capable of afluming and maintaining the form of gas ; for al- 

 though the gafeous oxide may be obtained in a great variety of ways by. dire£l: compofition, 

 as well as the decompofition of the carbonic acid, yet when pure it is exadly the fame 

 fubftance, having the fame fpecific gravity, requiring the fame quantity of oxigen to fatu- 

 rate it, and producing uniformly the fame proportion of carbonic acid, I remarked Indeed 

 formerly, that the gas obtained from charcoal (however well dried) mixed with the me- 

 tallic oxides, always yielded a little water, when burned in a receiver containing comr 

 mon air or oxigen gas, and this impurity was afcribed to hidrogen contained in the char- 

 coal itfelf. Now that this may really be the cafe, appears to be in fome degree confirmed 

 by the following experiments. 



A quantity of charcoal obtained by diftillation in iron cylinders, was introduced into a 

 retort without being moiftened. A great quantity of gas was in all produced, what came 

 over about the middle of the procefs confifted of carbonic acid and hydrocarbonate in the, 

 proportion of i to 18. * Two meafures of this waflied hydrocarbonate required r.6 mea- 

 fures of oxigen to faturate them, the products being one meafure carbonic acid gas with, 

 water. Another portion of the fame charcoal, which had for fome time been expofed to 

 St red heat in a covered crucible, was introduced into a coated glafs retort, and a ftrong: 

 heat being applied, a confiderable quantity of gas came over. This gas, except at the very, 

 commencement, fcarcely contained a veftige of carbonic acid ; two meafures of it required 

 1.25 of oxigen gas to faturate them, the produfts being water with only .55 parts of a 

 meafure of carbonic acid. Now by comparing thefe experiments together, it would appear 

 that the gas from the charcoal which had been fo completely deprived of it6 xnoifture, con- 

 tained bulk for bulk more hidrogen, and lefs carbon than the gas from that which had not 

 been dried ; this being the cafe, it can hardly be fuppofed that the hidrogen proceeded 

 from the decompofition of water, but muft have fomehow entered into the compofition of 

 the charcoal itfelf. The .total abfence of carbonic acid may be confidered as a further 



* The gas obtained in this way is extremely variable, and towards the beginning of tlie procefs I have 

 fbmetlmes met with traces of the gafeous oxide. ' • ' • 



proof 



