1880.] Compounds of Carbon with Hydrogen and Nitrogen. 153 



of the flame of hydrocarbons are not all concordant. Boisbaudran 

 notices, besides the four hydrocarbon bands, only two hazy bands in 

 the indigo. Watts (" Phil. Mag.," 1869 and 1871) and Piazzi Smyth 

 eive the same two bands somewhat wider, and resolved into a series 

 of fine lines. These two observers are in substantial agreement about 

 this part of the spectrum, but Piazzi Smyth notices in addition a 

 faint haze in the red below C. 



Plucker and Hittorf notice the entire absence in the flame of 

 defiant gas of the two bright groups of lines (blue and violet as 

 described below) characteristic of the flame of cyanogen, and the 

 presence of a series of dark lines on a violet background in a position 

 intermediate between those of the two cyanogen groups. A similar 

 description is given by Morren ("Ann. Ch. et Phys.," Mars, 1865). 

 Neither of these observers notices the two hazy bands above-mentioned. 

 The descriptions given by these authors of this series of dark lines 

 appear to relate to something not seen by the other observers. They 

 resemble in some respects the description of the corresponding part of 

 the spectrum of the electric discharge in vapour of sulphur, and we 

 think it highly probable that these lines were due to some compound 

 of sulphur derived from the sulphuric acid employed in preparing the 

 gas. 



Several observers also have described the spectrum of the flame of 

 burning cyanogen. Faraday, as long ago as 1829, called the attention 

 of Herschel and Fox Talbot to it, and the latter, writing of his obser- 

 vations (" Phil. Mag.," ser. iii, vol. iv, p. 114), points out as a peculiarity 

 that the violet end of the spectrum is divided into three portions with 

 broad dark intervals, and that one of the bright portions is ultra- 

 violet. More recently Dibbits, Morren, Plucker and Hittorf, have par- 

 ticularly described this spectrum. Dibbits (" Pogg. Ann.," 1864) 

 mentions in the cyanogen flame fed with oxygen, a series of orange and 

 red bands shaded on the less refrangible side (i.e., in the opposite way 

 to the hydrocarbon bands), the four hydrocarbon bands more or less 

 developed, a group of seven blue lines, a group of two or three faint 

 blue (indigo) lines, then a group of six violet lines, and, lastly, a group 

 of four ultra-violet lines. When the cyanogen is burnt in air the hydro- 

 carbon bands are less developed, and the three faint indigo lines are 

 scarcely visible, but the rest of the spectrum is the same, only less 

 brilliant. 



Plucker and Hittorf ("Phil. Trans.," 1865) state that in the flame 

 of cyanogen burning in air under favourable circumstances, the orange 

 and yellow groups of lines characteristic of burning hydrocarbons are 

 not seen, the brightest line of the green group appears faintly, the 

 blue group is scarcely indicated ; but a group of seven fluted bands in 

 the blue, three in the indigo, and seven more in the violet, are well 

 developed, especially the last. When the flame was fed with oxygen 



M 2 



