as produced and modified by Spark Discharges. 219 



with those seen in the arc ; second, that these bands cannot be due to 

 the effect of an alteration in temperature, giving rise to a second 

 spectrum of carbon ; nevertheless, as I have elsewhere pointed out,* 

 cyanides in a condensed spark do not produce this spectrum, no 

 matter whether they are extremely stable cyanides, such as that of 

 potassium, or those of the most easily decomposable character, such 

 as mercuric cyanide. This appeared to me to mark the inadequacy 

 of the facts derived solely from observations on the arc, to establish 

 the existence of a definite cyanogen spectrum. Moreover, it was 

 shown that lines somewhat resembling the edges of cyanogen bands 

 are seen when graphite poles are moistened with water and the 

 spark is passed through air; these lines are intensified and developed 

 into bands when the water contains ammonium chloride, calcium 

 chloride, or zinc chloride, and the bands become stronger as the solu- 

 tion used is more concentrated. 



If the lines observed are the edges of bands belonging to the 

 cyanogen spectrum, by what means do the chlorides give rise to their 

 production ? No one has yet supplied the answer to this question, 

 neither has it been proved that these lines in the spectrum of graphite 

 are the edges of cyanogen bands, though Ederf and Valenta state 

 that they are such because the wave-length measurements are 

 approximately the same. 



I believe that I am now able to offer an explanation of the action 

 of the concentrated solutions of chlorides, and to prove in addition, 

 that the bands and lines are really due to cyanogen and not to ele- 

 mentary carbon. 



If hydrochloric or any other mineral acid be carefully tested, it is 

 found to contain ammonia. The only ammonia- free acid is sulphur- 

 ous acid freshly prepared by passing sulphur dioxide gas into water, 

 carefully freed from ammonia and from any possible contamination 

 with it. If from the usual samples of so-called pure mineral acids, 

 salts of calcium or zinc be prepared, the ammonia salt present is not 

 eliminated, but it goes into solution and crystallises out with such 

 calcium or zinc compound, or, if the salt does not crystallise, it 

 remains in solution, and, as a consequence, the salt will show in its 

 solution the effect of a larger proportion of ammonium salt, accord- 

 ing to its degree of concentration. Hence if the bands, said to be 

 cyanogen bands, are due to the nitrogen of the ammonia present, the 

 spectrum of the graphite poles will exhibit the bands more strongly, 

 as there is less water in the solution. But this does not account for 



* ' Phil. Trans.,' vol. 175, p. 49, Part I, 1884, and ' Boy. Soc. Proc.,' vol. 55, 

 p. 344, " On Variations observed in the Spectra of Carbon Electrodes, and on the 

 Influence of one Substance on the Spectrum of another." 



t 'Wien, Akad. Wiss. Denkschriften,' vol. 60, 1893, "Line Spectrum ,of 

 Elementary Carbon." 



