SPECTEA OF VAEIOUS GASES. 
885 
most characteristic lines in the spectrum of carbon are the following: — At 123 a strong 
line, a weaker one at 127, two strong compound lines at 138 and 140, and an intense 
compound line at 153. 
With carbonic acid the special spectrum of silver appears much intensified. Some of 
the lines which appeared as dots in air are continued across the spectrum in carbonic 
acid. In carbonic oxide the intensity of the spectrum is less than in air ; and this contrast 
between the two gases may be observed whatever be the nature of the metallic electrodes. 
Fig. 35 exhibits the spectrum obtained between platinum points in carbonic acid. 
Fig. 36 shows the spectrum from gold points in carbonic oxide. Unfortunately in the 
Plate the figure is given a little too much to the right of its true position for accurate 
comparison with the spectrum above it ; but the principal lines will at once be recognized 
as coinciding, if allowance be made for this displacement. 
63. Olefiant Gas . — Some difficulty is experienced in observing the spectrum of this 
gas, owing to the copious deposition of carbon which occurs immediately that a current 
of sparks is transmitted. The natm'e of the electrodes employed seems to exert consi- 
derable influence upon this decomposition. It is extremely intense when aluminum 
electrodes are used, but comparatively slight with gold. Observations made when gold 
electrodes Avere employed exhibited a spectrum Avhich could not be distinguished from 
that of carbonic acid or of carbonic oxide. 
64. Marsh-gas . — Sparks pass freely in this gas. The spectra obtained with gold and 
copper electrodes cannot be distinguished from those of the same metals in carbonic acid 
and carbonic oxide. A scanty separation of carbon occurs during the passage of the 
spark. This is particularly evident when copper electrodes are used, the bluish light of 
the metallic spark being frequently accompanied by reddish yellow scintillations : the 
deposition of finely divided carbon upon the quartz plate on the side of the gas-tube 
impairs the intensity of the photograph. 
65. Cyanogen . — A difficulty was experienced in this case also in obtaining intense 
photographs, particularly when silver electrodes were employed ; a rapid deposition of a 
brown matter, probably paracyanogen, took place upon the interior of the tube. When 
copper electrodes were used, the light of the spark was sometimes of an intense green, at 
others of a pale blue. The photograph shoAved the particular lines due to carbon as 
well as those of nitrogen, and the special lines due to the metallic electrode employed. 
66. Sulphurous Acid . — This gas offers unusual resistance to the passage of the electric 
sparks, the electrodes requiring to be brought very close to each other before the 
disruptive discharge passed freely. This difference in the power of different gases to 
modify the striking-distance has already been examined by Dr. Faeadat*. A strong 
spectrum was obtained Avith gold wires: it terminated abruptly at 113-5, a single spot 
of renewed action appearing at 143-0. This result is due no doubt to the absorbent 
action of the gas, which has been already shown in a former section of this paper (18) to 
be one of the least diactinic of gaseous bodies. In this form of experiment the stratum 
* Philosophical Transactions, 1838, p. 103. 
6 E 
MDCCCLXII. 
