NATURE 



\_May 6, 1880 



" Nous avons produit le spectre primaire de I'azote avec 

 diffdrents corps qui n'ont absoKiment de commun que 

 I'azote ; nous pensons done avoir ddmontrd qu'il appartient 

 bien rdellement h ee mdtalloide." {Anna/es de Cheniie et 

 de Physique, 4 serie, tome xxviii. pp. 70, 71). 



In 1868 WuUner* gave his attention to tbis subject, 

 and strongly supported Plucker's view of the existence of 

 double spectra, indicating at the same time that the 

 difference of temperature must be regarded as the sole 

 cause of the phenomenon, adding, however, " a decom- 

 position with further elements is not to be thought of" 

 In the case of hydrogen he showed that the banded spec- 

 trum ascribed to acetylene really depended upon a change 

 in the emissive power brought about by an alteration of 

 temperature. Touching oxygen, he showed that three 

 distinct spectra may be obtained, while in nitrogen two 

 are observed. 



I may say that in my early laboratory experiments I 

 was at first led to think that, in the case of metallic 

 vapours. Angstrom's first expressed opinion was correct, 

 and I said so. But after more experience and knowledge 

 had been acquired, I was compelled by the stern logic 

 of facts to abandon it, and I showed, first, that more 

 " orders " of spectra — to use Plucker's term — were neces- 

 sary, and then that the line spectrum itself was in all proba- 

 bility compound ; that is, that it was in some cases built 

 up by the vibration of dissimilar molecules, some of which 

 might even give us a fluted spectrum, if we could study 

 them alone. 



Although, however, in the views I have expressed on 

 former occasions I have had the advantage of the support 

 of the opinion of Plucker and Angstrom, and later of 

 Dr. Schuster,- not to mention others, I am aware that 

 though there is a general consensus among spectroscopic 

 workers that double spectra cannot be ascribed to impuri- 

 ties, it is not absolute. 



I propose therefore in this place to refer to a special 

 case in which this question has been recently brought 

 prominently forward. 



I have already stated that Angstrom, who was the first 

 to map the line-spectrum of carbon, ascribed the fiutings 

 ordinarily seen in the carbon compounds to acetylene. 



Now Attfield, in 1S62, as a result of a most carefully 

 conducted and admirably-planned set of experiments, 

 came to the conclusion that the flutings were really due 

 to carbon : in short, '"that carbon, like hydrogen, iodine, 

 sulphur, nitrogen, and other bodies, had a fluted spectrum 

 as well as one consisting wholly of lines. 



The work of Attfield will be gathered from the following 

 extract from his paper {Pliil. Trans., vol. clii. part i, 

 p. 221 el seg.) : — 



" On recently reading Swan's paper by the light that 



^ Phil. Mag., sec. 4, vol. xxxvii. p. 405. 



^ Dr. Schuster's recently Jjubli^hed investigations are as follows : — 



Mr. Lockyer's investigations have shown that most tiodies give us a 

 continuous spectrum, as a gas, before they condense, and many at a con- 

 siderable temperature above the boiling point. Mr. Lochyer has rightly 

 drawn the conclusion /rotii these /acts, tliat the atomic aggregation of the 

 molecules is the cause 0/ the different orders of spectra. 



That the discontinuous spectra of different orders (line and band spectra) 

 are due to different molecular combination, I consider to be pretty well 

 established, and analogy has led me (and Mr. Lockyer bef c re me) to explain 

 the continuous spectra by the same cause; for the change of the continuous 

 spectrum to the I.ne or band-spectrum takes place in exactly the same way as 

 the change of spectra of different orders into each other. Analogy is not a 

 strong guide, yet some weight may be given to it in a case like the one under 

 discussion, where experiment hitherto has failed to give a decided answer. 

 (Dr. A. Schuster on the Spcc'ra of Metalloids, Phil. Trans. Royal Society, 

 1879. Part i p.ige 38 and £3, njte.) 



Professors Bunsen and Kirchhoff have thrown on the | 

 subject, I came to the conclusion that these bands 

 must be due to incandescent carbon vapour ; that, if so, 

 they must be absent from flames in which carbon is 

 absent, and present in flames in which carbon is present; I 

 that they must be observable equally in the flames of the 

 oxide, sulphide, and nitride as in that of the hydride of 

 carbon ; and, finally, that they must be present whether 

 the incandescence be produced by the chemical force, as 

 in burning jets of the gases in the open air, or by the 

 electric force, as when hermetically-sealed tubes of the 

 gases are exposed to the discharge of a powerful induction- 

 coil. . . . 



" To establish the absolute identity of the hydro- and | 

 nitro-carbon spectra, excluding of course the lines due to 

 nitrogen, they were simultaneously brought into the field 

 of the spectroscope : one occupying the upper, and the 

 other the lower half of the field. 



" This was readily effected after fixing the small prism, 

 usually supplied with spectroscopes, over half of the 

 narrow slit at the further end of the object-tube of the in- I 

 strument. The light from the oxyhydrocarbon flame was 

 now directed up the axis of the tube by reflection from 

 the little prism, while that from the oxynitrocarbon flame 

 passed directly through the uncovered half of the slit. A 

 glance through the eye-tube was sufficient to show that 

 the characteristic lines of the hydrocarbon spectrum 

 were perfectly continued in the nitrocarbon spectrum. 

 A similar arrangement of apparatus, in which the 

 hydrocarbon light was replaced by that of pure nitro- 

 gen, showed that the remaining lines of the nitrocarbon 

 spectrum were identical with those of the nitrogen 

 spectrum. In this last experiment the source of the pure 

 nitrogen light was the electric discharge through the 

 rarefied gas. 



" The above experiment certainly seemed to go far 

 towards proving the spectrum in question to be that 

 of the element carbon. Nevertheless, the ignition of the 

 gases having been effected in air, it was conceivable that 

 hydrogen, nitrogen, or oxygen had influenced the phe- 

 nomena. To eliminate this possible source of error, the 

 experiments were repeated out of contact with air. A 

 thin glass tube I inch in diameter and 3 inches long, with 

 platinum wires fused into its sides, and its ends prolonged 

 by glass quills having a capillary bore, was filled with pure 

 dry cyanogen, and the greater portion of this gas then 

 removed by a good air-pump. Another tube was similarly 

 prepared with olefiant gas. The platinum wires in these 

 tubes vv'ere then so connected with each other that the 

 electric discharge from a powerful induction-coil could 

 pass through both at the same time. On now observing 

 the spectra of these two lights in the simultaneous manner 

 previously described, the characteristic lines of the hydro- 

 carbon spectrum were found to be rigidly continued in 

 that of the nitrocarbon. Moreover, by the same method 

 of simultaneous observation, the spectrum of each of 

 these electric flames, as they may be termed, was com- 

 pared with the corresponding chemical flames, that is, 

 with the oxyhydrocarbon and oxynitrocarbon jets of gas 

 burning in air. The characteristic lines were present in 

 every case. Lastly, by similar inter-observation a few 

 other lines in the electric spectrum of the hydrocarbon 

 were proved to be due to the presence of hydrogen, and 

 several others in the electric spectrum of the nitrocarbon 

 to be caused by the presence of nitrogen. . . ." 



" The spectrum under investigation having then been 

 obtained in one case wlien only carbon and hydrogen 

 were present, and in another when all elements but car- 

 bon and nitrogen were ab=cnt, furnishes, to my mind, 

 sufficient evidence that the spectrum is that of carbon." 



" But an interesting confirmation of the conclusion just 

 stated is found in the fact that the same spectrum is 

 obtained when no other elements but carbon and oxygen 

 are present, and also when carbon and sulphur are the 



