492 



Prof. A. Sraitliells on the 



temperature it undergoes dissociation info carbon dioxide and 

 carbon. Victor Meyer (Pyrochemische UntersucJmngen,p. 61) 

 amply confirms this observation. There is good reason to 

 foresee, therefore, that under extreme conditions carbon 

 dioxide would be formed in a carbon monoxide tube and would 

 exhibit the spectrum proper to it. 



In describing the behaviour of carbon monoxide Liveing 

 and Dewar remark thnt at high exhaustion, when the oxy- 

 carbon spectrum is seen, much metal is thrown off the electrodes 

 during the discharge. I also have noticed the accumulation 

 of a black deposit at this stage, but the deposit is formed even 

 when aluminium electrodes are used. The deposit in mv 

 tubes was, in fact, carbon, and could always be removed by 

 admitting air or oxygen to the tube and sparking. The 

 behaviour of carbon monoxide under extreme conditions 

 appears therefore to conform fully to a changed condition 

 according to the established equation 



2CO-*C0 2 + C. 



It is very noteworthy that the deposition of carbon in a 

 sparking tube only arises when the contents are yielding the 

 carbon line-spectrum. If the Swan spectrum be due to 

 elementary carbon it is difficult to see why a deposit of carbon 

 is not formed in a tube even more readily when the contents 

 are yielding the Swan spectrum. 



4. Carbon dioxide gives most readily the oxycarbon spec- 

 trum, and this remains at high exhaustions. At ordinary 

 atmospheric pressure the gas gives only the line spectrum 

 of carbon and oxygen. A condensed discharge in a 

 Plucker tube favours the formation of the Swan spectrum. 

 This behaviour accords with the facts that carbon dioxide 

 is relatively a good conductor, but that when the heating 

 effect of the discharge is intensified the gas is dissociated into 

 carbon monoxide and oxygen. 



A condensed discharge in highly-rarefied carbon dioxide 

 produces the line spectra of carbon and oxygen. I have 

 never found the oxygen lines visible without the carbon lines 

 being also visible, so that there is no evidence of the gas being 

 split up easily into carbon monoxide and oxygen. 



An impression seems to prevail that carbon dioxide is an 

 easily dissociable gas, and that carbon monoxide is relatively 

 stable. The truth is exactly the reverse of this when" the 

 gases are heated statically as in a Plucker tube. Victor 

 Meyer found (loc. cit. p. 64) that carbon dioxide has almost 

 exactly the normal density even at 1 700 c ; whereas carbon 



