146 
ME. W. HUGGINS ON THE SPECTEA 
nitrogen, a few of the lines of common air are wanting, but no new lines appear. The 
lines of the air-spectrum which remain in nitrogen preserve unaltered their relative 
brightness and their distinctive characters. In the Tables these lines are distinguished 
by the letter N. 
The nitrogen was prepared by causing air freed from carbonic acid by potash, to pass 
over red-hot finely divided copper which had been previously reduced from the oxide 
by hydrogen. The nitrogen was then dried by sulphuric acid. The freeness of the 
nitrogen from oxygen and from moisture was shown by the total extinction of all the 
lines which did not retain their usual brightness, and the absence of any trace of the 
strong hydrogen line. Subsequently a fresh portion of nitrogen was prepared by the 
same method, and a portion of it sealed up at the common pressure in a glass tube of 
suitable form, pierced with platinum electrodes. This tube continues to give results 
identical with those obtained in the current of nitrogen. 
d. Oxygen — When a current of oxygen from fused chlorate of potash was substituted 
for nitrogen, the numerous lines of the nitrogen spectrum faded out, and those which 
were extinguished by nitrogen reappeared with an intensity greater than they possess 
when the spark passes in air. These are distinguished in the Tables with the 
letter O. 
No new lines were added to the spectrum, but an unexpected result was observed. 
Two (it may be, three) of the lines visible in nitrogen remained also in oxygen. The 
most noticeable of these is the double line 2642. This in the air-spectrum is not quite 
so strong as the line next in greater refrangibility. This brighter line became extinct 
in oxygen at the same time that the double line remained fully as brilliant as in air, if 
not a little exalted in intensity. This result, therefore, could not be due to any oxygen 
remaining in the nitrogen, or of nitrogen in the oxygen. The other line, which behaves 
similarly in oxygen and nitrogen, is theTiazy one in the red, 807. The line in the Tables 
marked with the symbols of nitrogen and oxygen, at 3456, is in the air-spectrum a 
double line. The narrow defined line of nitrogen is superposed upon the broader nebu- 
lous line of oxygen. Oxygen and nitrogen from other sources were then examined. 
Nitrogen was evolved from a mixture of nitrite of potash and chloride of ammonium. 
Oxygen was obtained from peroxide of manganese and sulphuric acid, also from bichro- 
mate of potash and sulphuric acid, and also from oxide of mercury. The gases thus 
prepared were identical in their action upon the spectrum with those previously 
examined. I have not at present carried this inquiry further. 
[I have carefully re-examined the lines which are apparently common to nitrogen and 
to oxygen. I now regard them as due to the superposition in the air-spectrum of lines of 
oxygen and of nitrogen. When the most remarkable of these, the double line 2642, is 
closely observed with the eyepiece of a power of 35 times, the double line, as a whole, 
appears to become in a slight degree more refrangible when the air is replaced by oxygen. 
As the oxygen lines of the air-spectrum become more brilliant in oxygen, the phenome- 
non observed may be explained by supposing a pair of unequally bright oxygen lines to 
