494 Prof. A. Smithells on the 



dioxide are passed into the arc the (Swan) spectrum is pro- 

 duced . . . the (Swan) spectrum is brought out at once in the 

 magnesia crucible by moistening one of the poles." They 

 also found that the spectrum of the arc taken in water shows 

 the Swan spectrum only. 



An explanation suggested by Liveing and Dewar for these 

 remarkable facts is that possibly the introduction of cool gas 

 or of moisture increases the resistance in the arc and causes 

 a higher temperature. It will be obvious how simple the 

 explanation becomes if the Swan spectrum be attributed to 

 carbon monoxide, for every condition found by Liveing and 

 Dewar to enforce the spectrum in question is equally a 

 condition to favour the formation of carbon monoxide. 



Having now summarized the evidence which supports the 

 view I have put forward with regard to the spectra of the 

 oxides of carbon I will deal with facts that may appear 

 opposed to it. 



1. The red line stated hj Pliicker to be characteristic of 

 carbon dioxide I have already dealt with (p. 488). I have 

 obtained no evidence of its existence. 



2. The supposed stability of carbon monoxide and insta- 

 bility of carbon have also been with (p. 492). 



3. The flame of carbon monoxide gives a continuous 

 spectrum, and if the light of this flame is due simply to the 

 formation of carbon dioxide, it may be asked why it does not 

 give the oxjcarbon spectrum. In answer to this question 

 there are several important considerations to be adduced, In 

 the first place there is no certainty that the process occurring 

 in the combustion of carbon monoxide is the same in its 

 chemical stages as that which accompanies the discharge of 

 electricity through carbon dioxide. Quite apart from the 

 part played by water in the combustion of carbon monoxide 

 (Dixon, Phil. Trans. 1884, ii. p. 629) we are dealing there 

 with the oxidation of ready formed carbon monoxide, whilst 

 in the electrolytic conduction of carbon dioxide we may be 

 dealing with the action between carbon and two atoms of 

 oxygen simultaneously. 



On the other hand, there is an observation recorded by 

 Burch ('Nature,' xxv. p. 165, 1886) to the effect that when 

 carbon monoxide is burned nnder reduced pressure the spec- 

 trum of the flame shows signs of becoming discontinuous, and 

 though the maxima of light are not well defined they are 

 located in positions which are not incompatible with the 

 supposition that they may be the vestiges of the oxycarbon 

 bands. 



