884 
PEOrESSOE W. A. MILLEE ON THE PHOTOGEAPHIC 
filled with the ^as under experiment (or, when practicable, the gas is disengaged during 
the experiment), and, after the apparatus has been connected with the induction-coil and 
adjusted in its proper position, a slow current of the gas at the atmospheric pressure is 
transmitted, the excess of gas as it passes out of the apparatus being conveyed into the 
chimney or out of the window by a suitable arrangement of tubes. 
A simpler apparatus was admissible when the wires could, like those of platinum or 
of iron, be soldered into glass. Fig. 50 shows this modification. A piece of tubing a, 
about an inch and a half long and half an inch in internal diameter, is united at each 
extremity to a piece of quill tubing e, e ; the wires d, d are then soldered through its 
sides. A portion of the wide tube is ground away as at b, leaving an opening to which 
the quartz plate c can be applied, and kept in its place by small rings of caoutchouc. 
The gas was transmitted through the tube as in the other form of apparatus. 
60. In one or other of these modes the following gases were submitted to experi- 
ment ; — hydrogen, carbonic acid, carbonic oxide, olefiant gas, marsh-gas, cyanogen, 
sulphurous acid, sulphuretted hydrogen, ammonia, protoxide of nitrogen, nitrogen, 
oxygen, chlorine, and hydrochloric acid. 
The general results of these experiments on the invisible rays are in harmony with 
o 
those already obtained for the visible ones by MM. Angstkom^, ALTEEf, and PLUCEEBij!. 
The conclusions at which I have arrived may be thus summed up : — 
1. Each gas tinges the spark of a characteristic colour ; but no judgment can be formed 
from this colour of the kind of spectrum which the gas will furnish. 
2. In most cases, in addition to the lines peculiar to the metal used as electrodes, new 
and special lines characteristic of the gas, if elementary, or of its constituents, if com- 
pound, are produced. When compound gases are employed, the special lines produced 
are not due to the compound as a whole, but to its constituents. 
3. The lines due to the gaseous medium are continuous, not interrupted or broken 
into dots. 
61. Hydrogen . — The spectrum of the spark taken in this gas is not characterized by 
any new lines. The most remarkable effect is the disappearance of the atmospheric hues, 
together with the great lowering of the photographic intensity, whether the metal 
employed be platinum, gold, silver, copper, iron, or zinc. It is interesting to observe 
that the characteristic lines of highly oxidizable metals, such as iron and zinc, are visible 
in hydrogen, though the impression on the plate throughout is very greatly reduced in. 
intensity 
62. Carbonic Acid and Carbonic Oxide . — The lines contained in the spectra of these 
two gases are identical ; new lines characteristic of carbon occur in addition to the lines 
due to the nature of the metallic electrodes. The same lines are visible when other 
compounds of carbon, such as olefiant gas, marsh-gas, and cyanogen, are employed. The 
* Poggendoeit’s Annalen, 1855, Bd. xciv. S. 141. f Silliman’s Journal, 1855, vol. xix. p. 213. 
J Poggendoeee’s Annalen, 1859, Bd. evil. S. 497. 
