352 On the Change which Carhonic Add Gas 



through all that fpace. I then thought that this inflammable 

 gas did not arife from the decompofition of the water, but 

 from that of the carbonic acid ilfelf by the metal. I indeed 

 found that this gas was not hydrogen gas, but carbonous gas 

 perfeftly pure. I burnt loo parts of it on mercury, with 

 about a third of oxygen gas. I did not perceive water after 

 this comburtion, which left for refiduum 77 parts of car- 

 bonic acid gas. 



The dilatation which the latter experiences by ele6lrifa- 

 tion may be explained by the different denfities of the car- 

 bonous gas and the carbonic acid gas. I was not able to 

 verify the obfervation of C. Monge refpefting the dilatation 

 experienced by the carbonic acid gas, after eleftrifation over 

 mercury. 



If it was not poflible to reduce entirely the acid gas into 

 carbonous gas by thefe proceflTes, it was becaufe the firft 

 ftrata of metallic oxidation prefented an obftacle to further 

 oxidation, by preventing the points of contaft. The deve- 

 lopment of the carbonous gas produced therefore an analo- 

 gous effect. 



It refults then from mv obfervations, that the change 

 which carbonic acid gas undergoes by eleftrifation does not 

 arife from the decompofition of the water, but from the par- 

 tial decompofition of the carbonic acid gas, which becomes 

 carbonous gas, giving up a part of its oxygen to the metal 

 introduced in thefe experiments. 



II. Decovipojttion of Carhonic Acid Gas by Hydrogen Gas. 



It was long fuppofed that carbonic acid gas could be 

 decompofed by hydrogen gas ; but no one was able to 

 effe6l it, though many experiments were made on that fub- 

 je«Si;. I had obfcrved, that a mixture of equal parts of hy- 

 drogen gas and carbonic acid gas, contained by mercury 

 and left to itfelf, had decreafed in volume in the courfe of a 

 year.. When I then caufed the refiduum of acid gas to be 

 abforbcd by potafli, and had burnt the hydrogen gas, I found 

 that there was formed in this combuftion carbonic acid gas : 

 but thefe refults were not very fenfible ; and what took place 

 in this operation was to me mere conjefture. Since that 

 time I have been able to confirm in a decifive manner this 

 fir(t obfervation, by caufing the eledlric fparks to circulate in 

 a mixture of carbonic acid gas and hydrogen gas. In a few 

 nioments I faw the volume of the gas dccreafe, drops of 

 water formed, and the acid gas pafs almoft entirely to the 

 ftate of carbonous gas. The following are the details of one 

 ©f thefe experiments : I introduced into a cylindric glafs jar 

 7 about 



