2o8 ~ jfddiiioftal Ohfervatlont en H^drocarbonates, 



with the reparation of much charcoal, and only a fmall proportion of carbonic acid ge- , 

 nerated; the remaining gas, which is inflammable, and in fmall quantity, appears to be 

 gafeous oxidci Thus then we find, that by combining the fame inflammable gas with 

 equal quantities of oxigen under different circumftances or combinations, very different 

 eflfefts may be produced. 



On a former occafion I remarked, that from the great facility with which the carbonic 

 acid was decompofed, when a mixture of clear iron filings and chalk were heated together 

 In a retort, it would appear that this acid at a high temperature might be decompofed, at 

 leafl partially, by any fubftance which had a confiderahle affinity for oxigen ; and that this 

 was the only method of obtaining the gafeous oxide in a flate of purity. As this is a 

 circumftance of confiderahle importance, the following experiments are given in further 

 confirmation of it : 



About an ounce of chalk, which had been previoufly expofed for about ten minutes to 

 a low red heat, was mixed with an ounce of very bright zinc filings, thefe were introduced 

 into a coated glafs retort, and expofed to a heat gradually incrcafed. A little carbonic acid 

 came over at firfl, but this was foon mixed with a large proportion of the gafeous oxide, 

 and by the time the contents of the retort were thoroughly red, nothing but pure inflam- 

 mable gas was difengaged, and in prodigious quantity. It would have been troublefome, 

 and in faft unnecefTary, to have collefted the whole, but portions of it were examined at 

 different periods of the procefs, and found to continue perfectly pure, and without any 

 fenfible mixture of carbonic acid gas. Indeed, before I made this experiment, I hardly 

 conceived it poffible, thai fo complete a decompofition could be obtained in fo fimple a 

 way. Before the gas had intirely ceafed to come over, the retort was removed, and its 

 contents examined. In the neck of the retort there was found a quantity of the oxide of 

 zinc in the form of flowers, lining its furface to a confiderahle extent : a little below this, 

 and clofe to the belly of the retort, there adhered a little metallic zinc which had fublimed, 

 but was very much tarnifhed ; what remained in the belly confifled of the zinc deftitute of 

 all metallic luftre, and mixed with an imperfeft lime. The pieces of zinc, or rather oxide, 

 crumbled between the fingers into a greyifh powder, and feemed to have intirely loft their 

 tenacity. It is unnecefTary to add, that the gas obtained was found when fired with 

 oxigen, &c. to have all the properties of the pureft gafeous oxide of carbon. The above 

 experiment fhews in the moft fatisfaftory manner, how the oxigen abflrafted from the 

 carbonic acid is difpofed of, for in the procefTes with the iron filings this was not fo manifeft 

 as might have been expedled. 



A mixture of very dry chalk and clean filings of tin were next expofed to heat in 

 a coated glafs retort ; the firfl produdis coUefted confifled of carbonic acid gas, and 

 the gafeous oxide in the proportion of 5 to 6. The fecond or middle portion con- 

 tained two thirds of its bulk of gafeous oxide, and what came over afterwards 

 confifled of one part carbonic acid, and three parts gafeous oxide. The quantity in all 

 amounted to feveral gallons. After the procefs the tin was found partly oxidated, and 



3 p"'^y 



