222 
ME. J. ATTFIELD ON THE SPECTEHM! OE CAEBON. 
tenth of an inch in diameter, was obtained, and gave, on examination by the spectro- 
scope, a brilliant well-defined spectrum. 
The spectrum thus produced corresponds in appearance with the description of that 
observed by Swan, excepting in the number of fine lines in each band of light. The 
yellow-green band, composed, according to the drawing accompanying Swan’s paper, of 
four lines, I find to contain six ; the green band to have five instead of two ; the blue 
five, that is one more than Swan noticed ; and the violet, beside being distinctly double, 
to have a faint hair-line between its two halves. Indeed, in this as in other spectra, the 
reduction of bands into groups of lines seems simply dependent on the refractive power 
of the spectroscope, an increased number of prisms causing greater dispersion of the 
spectrum, and, consequently, a division in a line or band that otherwise would appear to 
be single. 
Having thus reproduced a satisfactory spectrum of the flame of a hydrocarbon, I next 
turned my attention to that of a nitrocarbon. Rejecting prussic acid vapour, on account 
of its containing hydrogen, I chose cyanogen. Cyanide of mercury was heated in a 
retort, and the cyanogen thus produced cooled and dried by passing over fragments of 
fused chloride of calcium contained in the neck of the retort. Ignited and examined 
by the spectroscope, this cyanogen flame gave a splendid series of bands, and these 
became still more distinct and brilliant on feeding the flame with oxygen by the plati- 
num safety-tube already mentioned. Familiarity with the spectrum of hydrocarbon 
flames enabled me to detect it in this nitrocarbon light, other lines present being after- 
wards proved to be due to incandescent nitrogen. 
But to establish the absolute identity of the hydro- and nitro-carbon spectra, excluding 
of com'se the lines due to nitrogen, they were simultaneously brought into the field of 
the spectroscope, one occupying the upper, the other the lower half of the field. This 
was readily efiected after fixing the small prism, usually supplied with spectroscopes, over 
half of the narrow slit at the further end of the object-tube of the instrument. The light 
from the oxy-hydrocarbon flame was now directed up the axis of the tube by reflexion 
from the little prism, while that from the oxy-nitrocarbon flame passed directly through 
the uncovered half of the slit. A glance through the eye- tube was sutficient to show 
that the characteristic lines of the hydrocarbon spectrum were perfectly continued in 
the nitrocarbon spectrum. A similar arrangement of apparatus, in which the hydro- 
carbon light was replaced by that of pure nitrogen, showed that the remaining lines of 
the nitrocarbon spectrum were identical with those of the nitrogen spectrum. In this 
last experiment the source of the pure nitrogen light was the electric discharge through 
the rarefied gas. 
The above experiments certainly seemed to go far towards proving the spectrum in 
question to be that of the element carbon. Nevertheless, the ignition of the gases 
having been effected in air, it was conceivable that hydrogen, nitrogen, or oxygen had 
influenced the phenomena. To eliminate this possible source of error, the experiments 
were repeated out of contact with air. A thin glass tube, 1 inch in diameter and 
