igS 



NATURE 



\Dec. 30, 1880 



removing the last traces of air." So that in the case of 

 cyanogen with a trace of hydrogen present, the sparlc 

 persists in giving us the spectrum of hydrocarbon ; and 

 when we have naplithalin with a trace of nitrogen present, 

 it gives us tlie spectrum of nitrocarbon ! 



Attfield states that the spectrum in question is obtained 

 from pure dry cyanogen. " The ignition of the gases 

 having been effected in air, it was conceivable that 

 hydrogen, nitrogen, or oxygen had influenced tlie pheno- 

 mena. To eliminate this possible source of error the 

 experiments were repeated out of contact with air. A 

 thin glass tube one inch in diameter and three inches 

 long, with platinum wires fused into its sides and its 

 ends prolonged by glass quills having a capillary bore, 

 was tilled with pure dry cyanogen, and the greater portion 

 of this gas then renio\ed by a good air-pump. Another 

 tube was similarly prepared with defiant gas. The 

 plitinum wires in these tubes were then so connected 

 with each other that the electric discharge from a power- 

 ful induction-coil could pass through both at the same 

 ime. On now observing the spectra of these two lights 

 ji the simultaneous manner previously described, the 



characteristic lines of the hydrocarbon spectrum were 

 found to be rigidly continued in that of the nitrocarbon 

 Moreover, by the same method of simultaneous observa- 

 tion the spectrum of each of these electric flames, as they 

 may be termed, was compared with the corresponding 

 chemical flames, that is with the oxyhydrocarbon and 

 oxynitrocarbon jets of gas burning in air. The charac- 

 teristic lines were present in every case." 



" The spectrum under investigation having then been 

 obtained in one case when only carbon and hydrogen were 

 present, and in another when all elements but carbon and 

 nitrogen were absent, furnishes to my mind sufficient 

 evidence that the spectrum is that of carbon." 



Morren also adopted this method of producing the 

 spectrum by taking the spark of an induction coil in a 

 sufficiently rapid current of pure cyanogen at atmospheric 

 pressure. 



I have again repeated this experiment with cyanogen 

 under conditions which would seem to ensure that the gas 

 should be dry (see also Phil. Mag., 1875). 



The cyanogen was prepared by heating pure cyanide of 

 mercury, which was finely powdered and placed in a piece 



of combustion-tubing {a) drawn out at both ends. In this 

 it was repeatedly heated to the temperature of incipient 

 decomposition whilst a current of dry air was drawn over 

 it. One end of the tube was then closed by fusion at the 

 point _^, and the other bent round and fitted, as shown in 

 the figure, to a U-tube (/') containing phosphoric an- 

 hydride — the discharge-tube c was interposed between 

 this U-tube and a second U-tube (n' also containing phos- 

 phoric anhydride, the other branch of which was con- 

 nected to one end of a vertical tube e of more than thirty 

 inches in length, the lower end of which passed into 

 mercury contained in the bottle yj the upper portion of 

 which could be exhausted by means of the air-pump. 

 The connections with the U-tube were made by means of 

 perforated india-rubber stopper?, and the joints were 

 surrounded during the experiment by melted paraffin. 



The apparatus having been exhausted, the mercuric 

 cyanide was heated till the apparatus was filled with 

 cyanogen at atmospheric pressure ; it was then again 

 exhausted and again filled with cyanogen. After having 

 been thus exhausted and re-filled five or six times, the 

 spectrum of the spark between the wires at c was examined 

 at various pressures. The spectrum figured in my paper 

 in the Pliilosophical Magazine for October, 1869, was 

 obtained, the groups y and S, with which alone we are at 

 present concerned, being the brightest in the whole spec- 

 trum. Next careful search was made for the red hydro- 

 gen line. The cross-wires of a one-prism spectroscope 

 were accurately adjusted to the red line, as seen in a 

 hydrogen vacuum tube, and the spectroscope was then 

 directed upon the spark in the cyanogen. No trace of 

 the line could be observed. 



A second experiment was devoted to the examinatioii 

 of the spark in an atmosphere of naphthalin vapour, 

 from which nitrogen had been excluded as far as possible, 

 in order to ascertain whether the bands f and 5, which 

 Professois Liveing and Dewar attribute to cyanogen, would 

 be produced. Professors Liveing and Dewar are somewhat 

 in error in saying that I laid much stress on the occur- 

 rence of these bands in carbonic oxide. They were never 

 obtained very brilliantly from carbonic oxide (except under 

 pressure), but they are obtained brilliantly from a naph- 

 thalin vacuum tube. 1 have obtained them also from a 

 vacuum tube containing pure mar:h-gas (my note-book 

 remarks "5 very bright"), and as confirmation by an 

 independent observer, I would remark that Pliicker maps 

 them in the spectrum of a vacuum tube containing 

 mctliyl. 



The vacuum tube in this second experiment contained 

 pure solid naphthalin fused on the sides of the tube ; this 

 was placed in position so that the upper end passed 

 through one hole in an india-rubber stopper into a flask 

 filled with carbon dioxide ; a vertical tube of thirty inches 

 length passed through the second hole in the stopper of 

 the flask, and its lower end dipped below mercury. The 

 whole of the vacuum tube except the lowest portion was 

 surrounded by a wider tube containing melted paraffin. 



When the apparatus had been arranged, the experiment 

 was commenced by passing a rapid current of carbonic 

 acid through the vacuum tube, so as to fill the flask and 

 escape through the mercur)-. ■'Vfter passing the gas for a 

 considerable time, the lower end of the tube was closed 

 by fusion, the naphthalin all melted down into this end, 

 where it was made to boil violently, while the paraffin was 

 maintained at a temperature of about 220" C. After the 

 current of mphihalin vapour had lasted some time, the 

 upper end of the tube was closed by fusion, the tube 

 removed and cooled, and its spectrum examined. It gave 

 a spectrum in which the groups i and 6 were plainly- 

 seen. 



It is to be hoped that some independent observer will 

 repeat these experiments, so as finally to settle the ques- 

 tion of the origin of these bands of what I must still 

 call the "carbon " spectrum. W. M. Watts 



