SPECTEA OF IGNITED GASES AM) VAPOURS. 
17 
is bounded at the place formerly occupied by the second bright line of the character- 
istic group c. 
When the flame of cyanogen is fed by air, we observe under favourable circumstances 
no traces of the groups a and b, the least-refracted bright line of the group c faintly 
appears, d is scarcely indicated, but the groups e , f, g are fully developed, especially the 
last one, of a fine violet colour. 
46. In supplying the flame of cyanogen by air increasingly mixed with oxygen, we 
distinctly see two spectra overlying one another. One of these spectra (the spectrum of 
bands) giving way step by step to the other, the appearance is continually changed. 
The red bands only remained undisturbed, they became even more distinct by the 
increased intensity of the combustion. The adjacent group a is scarcely developed, 
evidently on account of an imperfect extinction of the overlying bands. 
The superposition of the two spectra introduces new details into the general configu- 
ration of the resulting spectrum. Thus, for instance, at a certain intensity of combus- 
tion the interval between the first and second bright line of the group b is divided by 
four fine bright lines into five spaces, the breadth of which decreases towards the violet 
part of the spectrum. Thus also in the large field containing the group c, the influ- 
ence of the spectrum of bands is rendered sensible by a particular distribution of shadow. 
47. Secondly, we submitted to a closer examination olefiant gas, H 4 C 4 , when burned 
either with oxygen or with air. We operated as we did in the former case of cyanogen ; 
only the gas, prepared by heating a mixture of alcohol and sulphuric acid, was previ- 
ously introduced into a gasometer. 
The luminous cone which exhibits the spectrum of vapour of carbon is of a fine blue 
colour, especially if the flame is fed by oxygen. 
48. In the spectrum thus obtained the characteristic groups a, b, c, and d appeared 
on a shaded ground. All these groups, especially the red one a, scarcely seen in the 
spectrum obtained by the combustion of cyanogen, are finely developed. The last line 
of b and d is slightly expanded ; but there is no trace whatever either of the bands of 
the spectrum of cyanogen, if burned in common air, or even of the groups e and g. 
Instead of these groups there is quite a new configuration. Equally distant from the 
place which the groups occupied in the former spectrum, a small well-defined black 
band was seen, bounded on the more refracted side by a violet space, which, being of 
great brilliancy where it touches the band, was shaded gradually till the spectrum, not 
extending beyond the place of the group g , was extinguished. This violet space is tra- 
versed by well-defined dark lines, equally distant from each other, but more apart than 
the shading lines we described in former cases. The black band is bounded on its less 
refracted side by a bright line, having the breadth of the lines of the characteristic 
groups, which at a certain distance was preceded by a more diffused violet light, tra- 
versed, like the brilliant one on the opposite side, by dark but less distinct lines. Here 
also the faint group f appeared. 
The distribution of light and shade producing the configuration just described i& 
MDCCCLXV. d 
