436 



NATURE 



[March 9, 1893 



VAN'T HOFF'S "STEREOCHEMISTRY." 



Stirdochimie. Nouvelle Edition de " Dix Anndes dans 

 I'Histoire d'une Thdorie." Par J.-H. van't Hofif. 

 R(?digde par W. Meyerhofifer. (Paris: Georges Carrd, 

 1892.) 



THE second edition of this work was very fully re- 

 viewed in these columns in 1887 (vol. xxxvii. p. 121), 

 and we will therefore content ourselves with noticing 

 briefly the new matter contained in the present edition. 



We must, however, premise that the stereochemistry 

 of the carbon compounds is based on the assumption 

 that the four riionad atoms or groups satisfying the four 

 affinities of a carbon atom are situated at the solid angles 

 of a tetrahedron, the centre of which is occupied by the 

 carbon atom itself, and on the allied conception of the 

 " asymmetric " carbon atom — " asymmetry '^ arising when 

 the four attached atoms or groups are dissimilar, in which 

 case two enantiomorphic arrangements are possible for 

 any given set of four such atoms or groups (see the 

 notice already referred to). In the first French edition, 

 which bore the title "La Chimie dans I'Espace," the 

 author discussed the greatly increased possibilities of 

 isomerism to which this new theory led. Since then 

 chemists have used the theory as a guide in the search 

 for cases of isomerism, and numerous new isomeric com- 

 pounds have been discovered, the existence of which 

 could not have been predicted as long as the old con- 

 stitutional formulas written in one plane were employed. 

 The history of this branch of organic chemistry has, 

 during the past seven or eight years, been one continuous 

 triumph for the theory. One of the most striking proofs 

 of the value of these stereochemical views is to be found 

 in Emil Fischer's well-known researches on the sugar 

 group. In the group of the glucoses of the aldehyde- 

 alcohol type, for example, the presence of four asym- 

 metric carbon atoms has to be assumed, and the theory 

 predicts the existence of no fewer than sixteen isomerides 

 with a normal carbon chain, as compared with the one 

 form admissible under the older view. Several of the 

 predicted forms have been prepared, and the relative 

 distribution of the positive and negative asymmetric 

 carbon atoms within the molecule has been determined 

 by E. Fischer. This and other work confir-matory of the 

 theory, is described and discussed in the present volume. 

 The theory of the asymmetric carbon atom owes its 

 origin to the difficulty of otherwise explaining the optical 

 rotatory power of various organic compounds. Quite 

 recently, P. A. Guye has suggested that the numerical 

 value of this optical rotatory power is dependent upon 

 the relative masses of the substituting atoms or groups 

 attached to the asymmetric carbon atom, and that if two 

 of the four different substituting radicles are of equal 

 mass the rotatory power will cease. He was unable to 

 verify this view in all strictness, since, in the cases of this 

 kind which he studied, such as that of methyl-ethyl- 

 aldehyde (CaH^) (CH3) CH(COH),inwhichC2H5 = COH 

 = 29, there was optical activity. The probable explana- 

 tion is, that, as suggested by Guye, not only the masses 

 of the groups, but also the interatomic distances, of 

 which the atomic volume is a measure, come into play 

 here. However, by varying the weight of a given group 

 NO. 1219, VOL. 47] 



attached to an asymmetric carbon atom — thus, by sub- 

 stituting successively different homologous radicles — it 

 was found possible to produce a concomitant variation in 

 the rotatory power of the compound, to make it increase 

 or decrease at will, and even to change its sign. This 

 variation is shown in ascending the series of the esters 

 of tartaric acid and its di-acetyl and di-benzoyl deriva- 

 tives. But whereas the weight of the alkyl-group in the 

 esters determines the amount of the rotatory power, no 

 such influence can be perceived in the case of the metallic 

 salts of tartaric acid, all of which display in solution the 

 same rotatory power, irrespective of the atomic weight of 

 the metal. The clue to this anomaly is furnished by the 

 electrolytic dissociation theory of Arrhenius, according to 

 which the dissolved salts are present in the form of their 

 dissociated ions, so that, in the case of the dissolved 

 metallic tartrates, it is the ion C02(CH.OH)oC02 which is 

 alone responsible for the rotation. Arrhenius's theory 



j thus receives striking confirmation from an unexpected 



I quarter. 



The subject of compounds containing closed chains is 

 fully discussed in the present edition, and the "cis" and 

 "trans" isomerism discovered by von Baeyer is de- 

 scribed. 



The relative position of the substituting groups in the 



i stereo-isomerides is also discussed. 



The concluding chapter deals with the stereochemistry 

 of nitrogen — a question which had not emerged when the 

 previous edition was published. Some of the information 

 given under this heading is rather meagre ; but doubtless 

 the omissions are intentional and they are largely com- 

 pensated for by a very complete bibliography of the 

 subject. 



The work is in every sense authoritative, and we cordi- 

 ally recommend it to all interested in the most recent 

 developments of organic chemistry. F. R. J. 



OUR BOOK SHELF. 



Die Fossile Flora der Hottinger Breccie. By R. von 

 Wettstein. With 7 plates. (Vienna : Imperial Print- 

 ing Office, 1892.) 



The Hottinger Breccia is a formation about 50 feet 

 thick in the neighbourhood of Innsbriick, and situated 

 about 1200 metres above sea-level. The upper part con- 

 sists of about 35 feet of coarse conglomerate, with fossils 

 chiefly confined to a bed some 3 feet thick, while the 

 remainder is occupied by alternating beds a foot or two 

 in thickness of white or reddish sandstones and breccias, 

 which are for the most part very fossiliferous. It has 

 been well known to collectors of fossil plants for upwards 

 of thirty years, and though at first regarded as of tertiary 

 age, is now uniformly recognised as quarternary, possibly 

 inter-glacial, or more probably post-glacial. The lower 

 part is characterised by the occurrence of many herbaceous 

 plants, such as the violet, strawberry, coltsfoot. Prunella, 

 &c., which are replaced above to some extent by Cornus 

 sanguinea, Rhatnnus Frangula, an alder, willow, &c., in- 

 dicating, perhaps, a change in the forest growth without 

 necessarily implying any considerable interval of time. 

 The flora is almost wholly of existing species, and in the 

 main does not differ essentially from that which might be 

 found in a similar situation at the present day ; but six of 

 the species no longer flourish at such an altitude, and a 

 few others, like the box, are absent in Northern Tyrol,. 



