204 On the Compoi'uion and Analysis 



lution hy water, which rendered it turbid, and of a whitish green 

 hue. This peculiar resinous matter appears to be a compound 

 of hydrogen and carbon : its vapour is perfectly decomposed by 

 passing it through a highly heated platinum tube, hydrogen be- 

 ing evolved, and carbon deposited. 



5. Mr. Faradav, whose accuracy as an operator is not in- 

 ferior to his assiduity as my Assistant in the Laboratory of the 

 Royal Institution, has shown in a ptiper published in the Quar- 

 terly .lournal of Science, that the supposed distinction between 

 olefiant and light hydrocarburet, by means of the action of 

 chlorine, has no foundation ; and that at common temperature, 

 all varieties of carburetted hydrogen are condefised by, and com- 

 bined with, chlorine. 



To ascertain how far the action of chlorine could be de- 

 pended upon as a means of analysing mixtures of olefiant and 

 hydrogen gases, I mixed equal volumes of chlorine and hydrogen, 

 over water at the temperature of 55", in a tube of half an inch 

 diameter, and exposed to ordinary daylight, but carefully ex- 

 cluded from direct sunshine. After twenty-four hours, the whole 

 of the chlorine had been absorbed by the water, and the origi- 

 nal volume of hydrogen remained unaltered. 



One volume of hydrogen mixed with one of olefiant gas and 

 two of chlorine, was reduced under the same circumstances to 

 very little more than one volume, the whole of the olefiant hav- 

 ing heen absorbed. 



In these cases it is convenient to use considerable excess of 

 chlorine, and in this way the purity of olefiant gas may be ascer- 

 tained : it will be found, even when obtained with every caution, 

 to afford a small residue of hydrogen ; but as this is sometimes 

 as little as one per cent, it may, generally speaking, be disre- 

 garded. 



6. The analysis of a mixture of hydrogen with carburetted hy- 

 drogen, carbonic oxide, and carbonic acid, presents peculiar dif- 

 ficulues in the ordinary mode of proceeding ; and as it often re- 

 quires to be performed in investigations relating to the gases 

 used for illumination, it became an object to facilitate the pro- 

 cess, for whicli I have used the following plan. 



A hundred measures of the gas are introduced into a gra- 

 duated tube, and the carbonic acid absorbed by a solution of 

 potassa ; the remaining gas is then transferred to thrice its volume 

 of chlorine of known purity, standing over water in a tube of 

 about half an inch diameter, and exposed to daylight, but care- 

 fully excluded from the direct solar rays ; after twenty-four hours 

 the carburetted hydrotieu and the excess of chlorine will have 

 been absorbed, and the remaining gas, consisting of carbonic 



oxide 



