18 
DRS. J. PLtJCKER AND J. W. HITTORF ON THE 
seen also, distinctly but faintly, in the spectrum we obtained by the combustion of 
cyanogen with oxygen, where at the same time the groups e and g are beautifully 
expressed (44). 
49. Am ong the gases exhibiting the spectrum of vapour of carbon, when enclosed in 
our spectral tubes and decomposed by the heat of the discharge of Ruhmkorff’s coil, 
we first select oxide of carbon. In operating with this gas as we did with nitrogen, 
we got, if the Leyden jar was intercalated, simultaneously the spectrum of vapour of 
carbon and the spectrum of oxygen ; without the jar, the pure spectrum of vapour of 
carbon. In the last case the heat of the discharge is high enough to ignite vapour of 
carbon, but not sufficient to give the spectrum of oxygen. The single spectrum, as well 
as the combined one, is obtained accordingly ad libitum ; whence we conclude that as 
the successive discharges pass through the spectral tube, the gas is alternately decom- 
posed and recomposed again. 
50. We shall in a few words describe the spectrum obtained without the jar, at a ten- 
sion of the gas, when observed by means of the manometer before the spectral tube was 
sealed, of 32 millims. 
Four characteristic groups only were seen, a, b , c, and d. When the current 
first passed, the band a appeared completely ; after some time its two first lines only 
remained, rising as isolated bright lines from a dark ground ; finally all the group dis- 
appeared. The groups b, c, and d remained nearly unchanged ; there appeared only 
two bright lines of c , the place corresponding to the two following ones being very 
brilliant. 
The whole spectrum was divided into large fields, similar to the fields we described 
in the case of the flame of cyanogen fed with oxygen. But in this case each field is 
bounded at its more refracted and shaded extremity by the first bright line of a charac- 
teristic group ; the following lines, bordered by shading, rise from the lightest part of 
the adjacent field. In the new instance the fields are not bounded in the same way. 
After the group a has disappeared, there is a differently shaded dark space, extending to 
the place of the third bright line of that group. In the remaining part of the spec- 
trum we may distinguish seven shaded fields. The first goes a little beyond the first 
bright line of the group 5, where it is bounded by a transversal line, dividing the band 
formed by the first two lines of the group into a dark less refracted and a light more 
refracted part. Accordingly the first bright line rises from the dark end of the first 
field, the remaining lines from the light end of the second field. The second field does 
not reach the first bright line of the following group c , this line being nearly equally 
distant from the extremity of the field and the next line of the same group. The third 
field goes slightly beyond Hp ; the fourth to the first line of the group d ; the fifth 
nearly to the place occupied by the fifth line of the group e ; the sixth approaches the 
place of the group/; and the seventh extends to the fourth line of the group g. The 
fourth and sixth fields presented the appearance of pure channeled spaces, as described 
in the case of nitrogen. 
