6io 



NATURE 



\Oct. 28, 1880 



\ 



containing the group C — O — . Briihl obtains a definite 



numerical value for the refractive power of each of these 

 groups. 



Now although the molecular refraction of isomers with 

 similarly linked, but differently grouped, carbon or oxygen 

 atoms is constant, the refractive indices and the densities 

 of these isomers are not the same. There is, therefore, a 

 definite connection between the densities and refractive 

 indices of carbon compounds, and the grouping, as dis- 

 tinguished from the linking, of the atoms in these com- 

 pounds. The densities and refractive indices of the 

 isomers, ethylene chloride and ethylidene chloride (see 

 ante) are not the same. Briihl has not determined any 

 exact numerical value for the refractive power of this or 

 that grouping of carbon or other atoms ; generally, how- 

 ever, he has shown that the more ramifications there are 

 in the structural formula of a carbon compound, the 

 smaller is the density and the smaller the refractive 

 index of that compound. Thus the density of butylic 

 iodide, CHs-CHa—CHj—CHol, is 1 -6 166, and the re- 

 fractive index (^i ) is 1-49601'; but the density of the 



CH,— CH— CH3 

 isomeric isobutylic iodide, | , is I '6056, 



CHoI 

 and the refractive index is i '49 192. 



Generally, then, it would appear that when rays of 

 light pass through a series of isomeric carbon compounds, 

 the isomerism of which is traceable only to differences in 

 the grouping of the constituent atoms, then that ray which 

 passes through the densest compound is more bent from 

 its original course than any of the other rays ; but that 

 when isomerism is due to differences in the linking of 

 the atoms, then the amount to which the rays are bent is 

 dependent not only on the density, but also on the 

 molecular "structure" of the compounds. 



Bruhl considers also the connection existing between the 

 boiling points, and other physical constants, of isomeric 

 carbon compounds containing only singly-linked poly- 

 valent atoms, i.e. compounds the isomerism of which is 

 due only to variations in the grouping of the atoms, 

 and the structural formula; of these compounds. His 

 results establish a considerable probability in favour of 

 the rule, that in such isomeric groups, those compounds 

 which Iiave the smallest molecular volumes, have also the 

 highest boiling points, greatest specific gravities and re- 

 fractive indices [not greatest molecular refractio/t)., and 

 longest time of tlow through capillary tubes ; and very 

 probably these compounds have also the smallest amount 

 of ramification in their molecular structure. 



Briihl thus put into the hand of the chemist another 

 means whereby he may readily learn much concerning 

 the inner structure of the substances which he examines. 

 Briihl's results, as also those of Thomsen, exhibit a close 

 connection between physical properties of compounds and 

 the valency, or specific saturation power, of the elementary 

 atoms which build up these compounds. 



As the theories of modern chcmibtry are so largely 

 based on the idea of valency, the results of Briihl and 

 1 homsen are most welcome, as at once tending to confirm 

 the general soundness of the methods of the Newer 

 Chemistry, and exhibiting at least two measurable 

 physical phenomena as closely connected with the e.\er- 

 cise of valency. 



The results of both observers emphasise the difference 

 which chemists have long recognised between two kinds 

 of isomerism: that due to " grouping," and that due to 

 "linking" of atoms. Is it not at least possible, in view 

 of these results, that a greater part of the chemical energy 

 of molecules containing doubly (or trebly) Imked poly- 

 valent atoms is kinetic, than is the case in isomeric mole- 

 cules, the atoms of which are all singly-linked ? if indeed 

 the chemical energy of the latter molecules be not wholly 



potential. Double-linking might then mean greater 

 kinetic energy ; and the entropy of a molecule containing 

 only singly-hnked atoms would be greater than that of its 

 isomer, some of the atoms in which were doubly-linked. 



The consideration of valency of atoms is closely con- 

 nected with the more general subject of chemical affinity; 

 and the work of Thomsen and Briihl suggests many 

 questions connected with affinity which press for answers. 



A short account was given in this journal (vol. xx. 

 p. 530) of the work of Guldberg and Waage, and of 

 Ostwald, on chemical affinity. The latter naturalist has 

 recently extended his methods of observation : in his 

 earlier papers he used physical methods, determining the 

 changes in the specific volumes, and also in the refractive 

 indices, of solutions of acids and bases when these acted 

 chemically on each other, and hence calculating the 

 amount of chemical action. Ostwald now employs a 

 more purely chemical method ; he allows acids of known 

 strength to react on a solid salt in excess, and determines 

 the amount of action at definite intervals. His results, 

 so far as they have extended,' strikingly confirm the 

 numbers which he before obtained for the relative affini- 

 ties of the commoner acids. 



The application of the theory of Guldberg and Waage 

 to reactions between a solid and a liquid, the former being 

 in excess, requires that a definite and stable condition of 

 equilibrium should be reached at the expiry of not too 

 great a time. Doubt was thrown on Ostwald' s results 

 because it was said that such equilibrium had not been 

 attained. In his latest paper Ostwald has carefully ex- 

 amined this point, and has shown that the required equi- 

 librium is attained, and maintained, and that therefore 

 such reactions are well suited for the study of general 

 problems of affinity. Ostwald' s future results, as he 

 extends the application of the chemical method, will 

 doubtless be very interesting. 



All the work wliich has been here shortly noticed tells 

 unmistakably that chemistry is rapidly passing out of 

 the natural history stage of progress into that stage where 

 her facts w ill be accurately grouped under general laws, 

 which laws will admit of quantitative statement, and of 

 quantitative deductions being made from them. 



The recent work in chemistry also illustrates the need 

 of a wide training in the methods of various sciences for 

 the investigator of this branch of natural phenomena. 

 One man begins with a purely chemical investigation, 

 another with one which appears wholly physical ; before 

 long they find that their paths meet, and that the problem 

 which each had attacked without thought of the other, can 

 be solved, and even then solved but partially, only by the 

 united effort of both. , M. M. Pattison Muir 



JAPAN"- 

 I. 



MR. MURRAY is to be congratulated on being able 

 to bring out simultaneously two such excellent 

 books on a country which for some years has probably 

 attracted more interest than any other country in the 

 world. Although they both treat of the same subject, 

 they differ much in their method of treatment. Indeed 

 the one may be said to be complementary of the other ; 

 and any one who reads them both with care will be able 

 to form a very complete idea of the present condition of 

 an unusually interesting country and people. Sir Edward 

 Reed went out practically as the guest of the Japanese 

 Government, and had ample opportunities of seeing the 



■ Hi: 



the Jo. 



nl /tir praclische Che. 



of the last and 



papers : 

 present year. 



- " Jnpan: its History, Traditions, and Religions, with the Narrative of 

 a Visit m 187Q." By Sir Edward J. Reed, K.C.B., F.R.S., M.P. Two 

 vols. With Map and Illustraticns. (London: John Murray, 1880.) 

 " Unbeaten Tracks in Japan." By Isabella L. Bird. Two vols. With 

 M.ap and Illustrations, (iiaaie Publisher.) 



