l62 



NATURE 



[June i6, i. 



Specific Heats of Cobalt and Nickel. Pure fused. 



. 8790 



Further experiments will be made, because a single well- 

 established case of this kind is sufficient to decide the question. 

 Already, however, I feel certain that Kopp's conclusion is right, 

 and that the law of Dulong and Petit, even for the metals, is an 

 approximation only, and cannot be expressed in the words of the 

 discoverers. For although the exact values of the atomic 

 weights of these two elements are not known, it is certain that 

 they are not so far apart as would be implied by these values for 

 the specific heats, even assuming that the value for nickel is, 

 as I believe, slightly too high. 



Two other examples of somewhat similar kind are shown by 

 gold and platinum, copper and iron. 



Specific Heats of Gold and Platinum. Pure fused. 



Gold S.G. —^ 19-227 Platinum S.G. ^^2 1-323 



For the gold I naturally applied to my colleague Prof. 

 Roberts -Austen, The platinum I prepared from ordinary foil 

 by re-solution, and reprecipitation as ammonic chloride, &c. 

 Both metals were fused into buttons before use. The atomic 

 heats come closer together than those of cobalt and nickel. 



Copper and iron differ considerably in melting-])oint, but both 

 at the temperature of 100° are far removed from even incipient 

 fusion. The copper was prepared from pure sulphate by elec- 

 trolysis, the iron by reduction of pure oxide in pure hydrogen. 

 Notwithstanding all our care, it was disappointing to find it 

 contained -or per cent, of carbon, the source of which I am at a 

 loss to explain. This iron is purer than any examined by 

 Regnault or Kopp. 



The differences observed between Co and Ni, and between 

 Au and Pt, are manifestly not due to allotropy or to differences 

 of melting-point, which in these cases can have no effect on the 

 result. 



So large a difference must be due to peculiarities inherent in 

 the atoms themselves, and differences of atomic heat are to a 

 certain extent comparable with the differences observed in other 

 physical properties which, like specific volume, specific refraction, 

 &c. , are approximately additive. 



If we try to think what is going on in the interior of a mass 

 of solid when it is heated, the work done is expended not only 

 in setting the atoms into that kind of vibration which corre- 

 sponds to rise of temperature — that is, it makes them hotter — but 

 partly in separating the molecules or physical units from one 

 another (= expansion), and partly in doing internal work of 

 some kind, the nature of which is not known. A difference 

 between metals and non-metals has been brought out by the 

 researches of Heycock and Neville, who find that metals dis- 

 solved in metals are generally monatomic ; whereas it is gener- 

 ally admitted that iodine, sulphur and phosphorus in solution 

 are polyatomic. It is, moreover, remarkable that although in 

 respect to specific heat each element in a solid seems to be inde- 

 pendent of the rest with which it is associated, when the separate 



NO. 1494, VOL. 58] 



elements are dispersed in vapour some rise in separate atom& 

 like mercury, some in groups of atoms Ij, Sg, AS4, P4, and these 

 groups, as the temperature is raised, are simplified with very 

 varying degrees of readiness. 



Sulphur vapour, for example, diminishes in density from 7^9 

 at 468°, to 4-7 at 606° (Biltz), that is, from about S, to S4, and 

 iodine from density 8 8 at 253°, to 5-6 at 1570° (V. Meyer), 

 that is, from about \^ to | L, but the dissociation of AS4 and 

 P4 begins only at much higher "temperatures, while with mercury 

 there is no corresponding change. 



But, although these groups are taken as the chemical molecules, 

 the physical unit in the solid is certainly the atom, whether 

 united by combination or mere mixture. 



The two metals, cobalt and nickel, with which I began my 

 inquiry, have nearly the same atomic weight, but they differ 

 from each other remarkably in chemical properties. For 

 example, nickel forms a compound with carbonic oxide ; on the 

 other hand, cobalt produces many remarkable ammoniacal com- 

 pounds, to which there is nothing corresponding among the 

 compounds of nickel. 



Having put aside the common excuses for the observed 

 divergencies from the law of Dulong and Petit, we are compelled 

 to look round for some other hypothesis. 



The constitution of carbon compounds is now explained by a 

 hypothesis concerning the configuration of the carbon atom 

 introduced by Van t' Hoff and Le Bel twenty- five years ago, and 

 which is now accepted by the whole chemical world. It seems 

 not unreasonable to apply a similar hypothesis to the explana- 

 tion of those cases of isomerism which have been observed in 

 certain compounds of the metals, notably chromium, cobalt, and 

 platinum. This has already been done by Prof. Werner of 

 Ziirich. Of course, as there is no asymmetry, there are no optical 

 differences in the pairs of compounds thus represented. If the 

 constitution of compounds can be safely explained by such hypo- 

 thesis, this implies peculiarities in the configuration of the indi- 

 vidual constituent metals around which the various radicles are 

 grouped in such compounds, and hence peculiarities in the 

 behaviour of such metals in the elemental form may possibly 

 be accounted for. For the atom of cobalt. Prof. Werner 

 employs the figure of the regular octahedron. For nickel, 

 therefore, which differs from cobalt, especially in yielding the 

 remarkable carbonyl compound discovered by Mond, and by 

 not yielding ammines like those of cobalt, and in other ways, a 

 different figure must be chosen. This, however, is for the 

 present a matter of pure speculation. 



SCIENCE IN THE THEATRE. 



'PHE assimilation of nature on the stage ! To what extent 

 ■^ is assimilation possible, and what are the necessary methods 

 and appliances for obtaining a satisfactory assimilation ? This 

 practically was the subject of a very valuable paper prepared 

 for the Society of Arts by Mr. Edwin O. Sachs, the architect, 

 which led to an animated discussion at the crowded meeting 

 before which it was read. The title of Mr. Sachs' paper, it is 

 true, was briefly " Stage Mechanism," but he went far beyond 

 the mere description of the various appliances that can be used 

 for obtaining certain scenic effects, and, more especially in his 

 introduction, treated the subject on broad lines. 



Though the presentation of drama and opera with some 

 attempt at realistic surroundings is now accepted as a matter 

 of course in all civilised countries, it can but rarely be said that 

 the attempts are successful. In fact, only of recent years has 

 the London manager been able to give us the presentation of 

 indoor scenes with some claim to merit, and this only by 

 building up his various scenes piecemeal in a most cumbersome 

 way, which is all that is possible where the changes of scene 

 are few and the " run " long. As to the presentation of scenes 

 out of doors, the London manager has most lamentably failed, 

 no matter how well painted individual canvases may have been, 

 or how tricky the arrangements of individual scenic effects. A 

 sky that looks like so much blue calico hanging on a wash-line, 

 a horizon with angles, a tree that looks like a piece of card- 

 board, or a moon which suddenly rushes into the sky and then 

 remains stationary, are all anomalies, and form only a few of 

 the innumerable details which tend to make a scene incongruous. 

 Now according to Mr. Sachs, who fully recognises the 

 attempts that have been made from time to time by Sir Henry 

 Irving, Mr. Beerbohm Tree, Sir Augustus Harris, and others 



