Page:Proceedings of the Royal Society of London Vol 60.djvu/240

Rh 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 solution 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 elementary carbon.

If hydrochloric or any other mineral acid be carefully tested, it is found to contain ammonia. The only ammonia-free acid is sulphurous 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, according 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

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.”
 * ‘ Phil. Trans.,’ vol. 175, p. 49, Part I, 1884, and ‘ Roy. Soc. Proc.,’ vol. 55,