1880.] On the Spectra of the Compounds of Carbon, SfC 505 



to their ends. Two narrow glass tubes were also passed through the 

 cork, one reaching the whole length of the bigger tube for the intro- 

 duction of gas, and the other a short one for exit. The tube was first 

 filled with nitrogen. On passing the spark we observed, as Angstrom 

 and Thalen say, that about the poles the nitrocarbon bands were 



plainly seen ; and they were visible through a great range of variations 

 of the character of the spark ; even the use of a condenser of moderate 

 size (a litre flask full of sulphuric acid and coated to the neck with 

 tinfoil) did not diminish them. Photographs were then taken, with 

 and without the use of the condenser, and these showed the violet and 

 ultra-violet nitrocarbon bands including those near N" and P. The 

 nitrogen was now swept out by a current of carbonic acid gas, and on 

 now passing the spark the nitrocarbon bands could no longer be detected, 

 and photographs taken as before showed no trace of any of them. 



In order further to test the sensibility of the spectroscopic test for 

 nitrocarbon compounds, and the permanence of such compounds under 

 variations in the electric discharge, we drew out, so as to form long 

 narrow necks, both ends of a glass tube of 110 cub. centims. capacity 

 which had wires sealed into it in the same way as before, and into one of 

 these necks we introduced, a minute quantity, '002 grm., of mercury 

 cyanide ; a current of hydrogen was then passed through the tube at 

 atmospheric pressure, and when it was judged that the air must be 

 thoroughly expelled, the tube was closed by the blowpipe. On passing 

 the spark no trace of nitrocarbon bands could be seen. The mercury 

 cyanide was then heated to decomposition by a spirit lamp. The 

 nitrocarbon bands immediately made their appearance, and were well, 

 even brightly seen, and they did not disappear when a strong spark 

 from a very powerful induction coil was passed, or even with the use 

 of a condenser consisting of two such flasks as are above mentioned. 

 There was no sign of any permanent decomposition of the cyanide ; 

 the bands continued to show well after the passage of the spark had 

 been maintained for a long time. The whole quantity of cyanogen 

 which the amount of cyanide introduced would give if it were wholly 

 decomposed, which is not the case at the temperature employed, is less 

 than g-g-o of the volume of the whole tube, i.e., of the hydrogen with 

 which it was mixed. % 



It appears from this experiment not only that the test is an extremely 



