the Intensity of the Lines of the Carbon Spectrum. 205 



It will be noticed that in the first set of experiments the 

 hydrogen line appeared slightly the stronger with 5 per cent, 

 hydrogen in the mixture, whereas in the second set the 

 carbon line was slightly the stronger with the same per- 

 centage. This is probably due to the fact that the vessel 

 containing sulphuric acid through which the gas bubbled 

 was, after each experiment, left full of the mixture just used,, 

 so that this contaminated, especially at first, the next mixture. 

 In the first case 5 per cent, hydrogen was tried immediately 

 after 50 per cent, hydrogen, so that probably the hydrogen 

 was somewhat in excess of 5 per cent, during most of the time. 

 In the second case the preceding mixture contained mostly 

 carbonic acid, so that in this case the hydrogen would pro- 

 bably be slightly less than 5 per cent, in the mixture during 

 most of the time. It is likely, therefore, that with 5 per cent. 

 hydrogen in the mixture the two lines are about equally strong. 



As before stated, the violet strong line of carbon is not 

 affected to this extent ; it was examined in each experiment^ 

 and it merely suffered a natural weakening as the proportion 

 of carbonic acid diminished, but it was quite distinct with 

 90 per cent, of hydrogen in the mixture, and easily visible 

 with still more hydrogen. 



Before proceeding any further the effect of nitrogen (or 

 rather, air) was tried ; this simply weakened both carbon lines 

 more or less equally ; with 80 per cent, of air, for example, 

 both carbon lines were quite distinct and fairly bright. 



The experiments were now repeated, using higher disper- 

 sion so as to separate the two red lines still further. Two 

 prisms of dense glass were used, and a small screen was fixed 

 in the eyepiece, which could be moved along horizontally by 

 means of a screw-head so as to cover up the hydrogen line, 

 and hence to eliminate all possibility of optical illusion due 

 to contrast effects. The results were substantially the same 

 as before ; it appeared that with 50 per cent, of hydrogen 

 the carbon red line is still faintly visible but not readily dis- 

 tinguishable — it seemed to flash in and out faintly rather 

 than to be faintly persistent. At times I thought it was 

 present, at other times I was sure it was not, so that its 

 presence seemed to depend upon very unstable conditions. 



B. Spark in mixture of Carbon Monoxide and Hydroaeu. 

 (i.) 19 parts H in 38 parts mixtare = 50 per cent. H. [Hydrogen line very strong; 









carbon line hardly visible.] 



(ii.) 1 



20 



, = 5 per cent. H. 



[Lines about equal.] 



(iii.j 9 



„ 32 



, =28 per cent. H. 



[Hydrogen line strong, car- 

 bon line faint.] 



(iv.) 22 



» 44 



„ =50 per cent, H. 



[Carbon line hardly distin- 

 guishable.] 



