April 2), 1890] 



NATURE 



513 



The Spectrum of Subchloride of Copper. 



It is noticed in Nature (vol. xli. p. 383), as the substance 

 of a paper read to the Academy of Sciences in Paris, on the 

 loth ult., by M. G. Salet, on the blue flame of common salt, 

 and on the spectroscopic reaction of copper-chloride, that the 

 strongest lines of the former flame, in the indigo and blue, are 

 due to copper-chloride, and coincide with bands given in M. 

 Lecoq de Boisbaudran's " Spectres Lumineux." 



Copper and chlorine appear, from the easy formation of 

 copper- subchloride, to have a very unstable affinity for each 

 other ; and the readiness with which copper itself seems to 

 volatilize, as shown by Mr. John Parry, in his spectroscopic 

 experiments for the Ebbw Vale Steel-making Company in 

 Wales, on the detection of impurities in iron and steel, by the 

 free and wide diffusion of its vapours compared with those of 

 other metals to a distance from a blowpipe flame, would per- 

 haps tend to promote dissociation and to the production of sub- 

 chloride from chloride of copper, at least in the presence of 

 reducing-gases, in a flame. 



There is a considerable general resemblance in respect of 

 place and brightness between the groups of lines belonging to 

 chlorine, and those belonging to copper-chloride, as those two 

 spectra are represented in M. Lecoq de Boisbaudran's work. 

 But the two spectra are of course very far from showing any 

 precise coincidences with each other. My attention was drawn 

 some time ago (in July 1878, Nature, vol. xviii. p. 300) to a 

 set of line bands of this same description, in very near corre- 

 spondence, apparently with the chief lines of the copper- 

 chloride spectrum, which presented itself in a violet-blue flame 

 seen very frequently in ordinary fires when they have been fed 

 with almost any kind of household dust and rubbish. But the 

 remarkably neat triplet of line-pairs — green, blue, and indigo — 

 in this blue fire-flame's spectrum could only be recognized as 

 very indistinctly matched by those chief lines of the spectrum 

 of copper-chloride, as those are produced, for instance, by in- 



Lankester's attention to this passage, and as it appears evident that he has 

 not referred to my original letters in Nature, I conclude that he does not 

 know how completely I there recorded my obligation to the article by 

 Darwin which really first did eneender the doctrine of panmixia. But, be this 

 as It may, the following is what I wrote : — 



" In a former communication I promised to advance what seemed to me 

 a probable cause -additional to those already known— of the reduction of 

 useless structures. As before stated, it was suggested to me by the pene- 

 trating theory proposed by Mr. Darwin, to which, indeed, it is but a 

 supplement" (1874). 



Again, in 1887, while anticipating and greatly extending Prof. Lankester's 

 present criticism touching Mr. Spencer's attitude with respect to panmixia, 

 1 said: — ' 



"The leading idea in Mr. Darwin's suggestion was that impoverished con. 

 ditions of life would accentuate the principle of economy of nutrition, and 

 so assist in the reduction of useless structures by free intercrossing. N )W, 

 in this idea, that of the cessation of selection was really implied ; but neither 

 m his own article, nor in a subsequent letter by Mr. George Darwin on the 

 same subject (^fATURe, October 16, 1873), was it exhibited as an inde- 

 pendent principle. Ic was inarticulately wrapped up with the much less 

 significant principle of impoverished nutrition." 



The simple history of the matter, therefore, is as follows. Even up to the 

 time of publishing his article in Naturr, Mr. Darwin had not perceived the 

 principle of panmixia as an "independent principle "—any more than Dr. 

 Dohrn perceived it in 1875, or Prof. Lankester perceived it in 1880,— which 

 niust act in all cases of degeneration, whether with or without the co-operation 

 of reversed selection in the economy of growth, "impoverished conditions," 

 &c. Iherefore, in the sixth edition of the "Origin of Species," after 

 having explamed the phenomena of degeneration by the inherited effects of 

 disuse, combined with ihe economy of growth, he proceeds to give very good 

 reasons for concluding that '"some additional explanation is here requisite 

 which I cannot give " ; and he suggests that, " if it could be proved that 

 every part of the organization tends to vary in a greater degree towards 

 diininution than towards aug nentation of size, then iv? should be able to 

 understand how an organ which has become useless would be rendered, 

 tniependently of the effects of disuse, rudimentary," &c. But although he 

 thus saw the "explanation" that was "requisite," he said he was unable to 

 give it ; therefore at that time he could not have seen that the cessation of 

 selection was exactly the explanation of which he was in search— to wit, a 

 principle which must always make every unused part of the organization tend 

 to degenerate. Later on, however, it occurred to him that " impoven.shed con- 

 ditions, combined with intercrossing, might lead to this re^ult. But, al- 

 though he thus came to such close quarters with the idea of panmixia that 

 he immediately suggested it to me on reading his exposition, the idea was still 

 entangled with that of " impaveri'hed conditions " being required in order to 

 starve the degeneratine; parts. Therefore, the only hand that I had in the 

 niatter was to liberate the all-important principle of panmixia from the toils 

 ot this entanglement, and thus to show that it must necessarily act in the 

 case K>\all unused structures, with the result of destroying the evidence of 

 the effects of disuse." 



Such is a simple history of the facts ; and my only object in previously 

 alluding to the part which I had played in the matter was not that of claiming 

 priority touchmg so very obvious an "idea," but in order to show h .w it 

 was that Mr. Uarwin, through all the editions of the " Origin -f Speues," 

 c mtinued to attribute important weight to a line of ev.d-nce in favour of the 

 innerited effects of disuse, which the doctrine of panmixia, and the doctrine 

 oj panmixia alone, has entirely destroyed. 



troducing into a Bunsen-flame a piece of copper-foil well wetted 

 with hydrochloric acid ; and no counterpart at all to them, 

 any more than to the ordinary chloride of copper spectrum, 

 could be traced in the well known blue fire-flame of common 

 salt, in whose spectrum, when pure, as well as in that of the 

 equally familiar blue fire- flame (when pure also) of carbonic 

 oxide, I do not remember to have ever detected any lines or 

 bands of greatest brightness so obviously discernible and distinct 

 as to admit of measurements. 



In the case of a copper-melting furnace, round the loose 

 junction of whose lid small escaping bodies of blue flame, on 

 one of the days on which I analyzed them, showed the well- 

 defined triplet spectrum very neatly, it was afterwards mentioned 

 to me (when that observation had been noted at the above place 

 in Nature), that pieces of ships' old copper- sheathings were 

 sometimes put into the copper-meltiiig pot ; and just as the use 

 of logs of broken-up ship-timber (as was also stated at that 

 place in Nature) explained a gorgeous blaze of this flame's 

 fine blue colour in a London house-fire very satisfactorily, so 

 foreign importations by salt into waste-materials from seaworn 

 ships, might by such a practice's occurrence as this in the 

 melting furnace, account very well for the presence of chlorine 

 along with copper in the furnace efflagrations which showed the 

 neat and easily recognized line-spectrum on one of the days of 

 my spectroscopic examinations of them, very plainly. Neglected 

 scraps of brass and copper become, however, so soon contamin- 

 ated with chlorine in nearly all situations, that it suflices, in 

 general, to throw any rusty piece of them, sujh as an old, dirty 

 piece of thin brass or copper wire, among the glowing coals of 

 a bright fire, to produce this peculiar-spectrumed blue flame in 

 the hottest crevices of the fuel. 



The nature of this flame, since it differs very materially, by 

 the simplicity of its spectrum, from the ordinary one of chloride 

 of copper, although in the strong point of line-positions there is 

 a partial feature of similitude in the spectra of the two flame-; by 

 which they agree very nearly with each other, remained a 

 mystery to me for several years ; but about four years ago I 

 chanced by good fortune to hit upon a compound, in some ex- 

 periments on subchloride of copper, which yielded in a flame, 

 at least a successful imitation, if not, as seems most probable, 

 the really natural and perfectly exact reproduction of it. Copper 

 subchloride is easily obtained by evaporating hydrochloric acid 

 to dryness in an open dish on an excess of wire clipping-; or 

 other small fragments of metallic copper. It is a dark greenish- 

 brown powder, which easily deliquesces, and by absorbing 

 oxygen, if exposed to the air, is soon converted into the green 

 chloride of copper. For the spectroscopic purpose it should be 

 dissolved when first formed, and dry, in about its own weight of 

 hot glycerine, and the solution be allowed to cool in a well- 

 corked bottle. This pasty solution inflames, when heated on a 

 wire, and burns with the peculiar-spectrumed violet-blue flame 

 which is observable in common fires when contaminations of 

 copper by chlorine are introduced among the fuel, in its hottest 

 parts. Although these contaminations in the state of exposure 

 to common air probably all consist of ordinary chloride of 

 copper, yet among the interstices of the fire, by the presence of 

 hot fuel and great abundance of carbonic oxide, they doubtless 

 undergo reduction to subchloride, and, in place of the many 

 lined and banded green-flaming spectrum of ordinary copper- 

 chloride, the far simpler and symmetrically grouped one nf 

 three line-pairs — green, blue, and indigo — belonging to sub- 

 chloride of copper vapour presents itself in the fine bluu 

 tint which the fire's flames assume, one may suppose, by 

 chloride's reduction to subchloride, and by the infinitesimal ad- 

 mixture in them of this latter foreign substance. The varieties 

 of tint, from blue below to green above, which a Bunsen-flame 

 exhibits when chloride of copper is introduced into it, are 

 probably due to the same chemical conversion, in dependence 

 on the reducing or oxidizing constitution of the flame in its inner 

 and outer layers, which most purely exhibit the two different 

 colorations. 



To produce the subchloride of copper spectrum very purely, 

 the thinnest possible smear of its pasty solution in glycerine, 

 on one side of a narrow strip of paper, suffices very amply, 

 since its colouring effect upon the flame, when the strip is rolled 

 up into a spill and lisjhted, is very powerful. Chlorate of 

 potash powder, kneaded up with the glycerine solution, burns 

 also self-supportingly with the characteristic rich blue colour, 

 but the spectrum in this case, and also when the paper stain of 

 the glycerine solution is left long exposed to air upon the strip 



