146 



NA TURE 



[Junk 13, 189; 



I 



might be based upon a more extended theor>', such as 

 that of Sohncke or that of Fedorow and Schonflics, and 

 would lead to all known varieties of crystal symmetry. 

 Such a deductive method is not, however, one which has 

 ever commended itself to scientific teachers in this 

 country, and it is not one which can be logically .idopted 

 in a book dealing solely with the morphology of crystals. 



The second method is the one introduced by C.adolin ; 

 it inquires in how many ways a figure obeying the law 

 of rational indices can be symmetrical according to the 

 number and distribution of its planes and axes of sym- 

 metr>', and it leads satisfactorily to all the known varieties 

 of cr>'stals. It was employed by Liebisch, and has been 

 carried to its utmost extreme in the new edition of Groth's 

 " Physikalische Krystallographie," where the systems arc 

 geometrically little more than artificial groups constructed 

 by synthesis of the various types, the conception of mcro- 

 symmetry being completely abandoned. Prof Maskelyne 

 treats of planes before axes of symmetry, and regards the 

 latter as begotten by the former; accordingly he is com- 

 pelled to introduce the idea of mero-symmetry as a second 

 empirical law, whereas the method of (iadolin requires 

 the one law of rational indices alone. In the opinion of 

 the present writer, (iadolin's is the most, indeed the 

 only, logical process. It must, however, be confessed 

 that the method of Prof Maskelyne possesses a sim- 

 plicity which is important from the educational point 

 of view, and might alone be sufficient justification for 

 its use ; that he has considered and rejected other 

 possible courses is clear from the discussion on p. 171, 

 which leads to the following suggestive remark : " It is, 

 however, evident that the whole treatment of crystal- 

 lographic symmetrj- on the assumption of planes and 

 axes of symmetry, actual or potential, represents a geo- 

 metrical abstraction ; an abstraction that needs for its 

 development and due explanation a complete science of 

 position applied to the molecular mass-centres." 



In the preface it is stated that the greater part of the 

 present treatise has long been in print ; this being the 

 case, the earlier part must inevitably be somewhat out of 

 touch with recent discovery, and since there is no list of 

 errata, statements which are not, like the geometrical 

 propositions, unassailable, must be received with due 

 caution. Thus milk-sugar is stated to be orthorhombic, 

 it has recently been proved mono-symmetric ; the whole 

 of § 314 should now be cancelled. Again, § 140 must be 

 read in the light of § 266. Cuprite is described both as 

 holo-symmetrical and as hemi-symmetrical ; but the 

 intelligent reader will find the most important of such 

 contradictions implicitly corrected in a table of crystalline 

 types, with authentic examples, given on p. 502. This 

 table is introductory to eight useful plates which deserve 

 special .attention, since they represent all the varieties of 

 merohedra and their relations, and render the previous 

 descriptions cisily intelligible. 



The appearance of this book is an interesting event in 

 the history of crystallography. The volume stands as a 

 striking and permanent record of the original manner in 

 which this science has for many years been treated by 

 the Oxford Professor in lectures, of which the substance 

 is now for the first lime made public. IJy those who 

 have had the privilege of personal acquaintance with his 

 (caching, it will be welcomed as the familiar echo of a 

 NO. 1337. VOL. 52] 



style of exposition singularly adapted to kindle en- i 

 ihusiasm for an abstruse subject, and by the scientific ' 

 public, as an authorit.-itive treatise on a science of which 

 the growing importance is continually becommg more 

 fully recognised. H. .\. iVIiers. 



THE STUDY OF STEREOCHEMISTRY. 

 Stt'reoiitimie. Exposi' des theories de Le /ie/ et Va)H 

 Hoff. Par E. G. Monod, avec une preface de M. C. 

 Kriedel. (Paris: (7authier-Villars et Fils, 1895.) 



THIS is a small Ijook of 162 pages which gives a cUiir 

 account of the fundamental ideas upon which is 

 founded the modern doctrine of chemistry in space, which 

 sprang, as every one knows, out of Pasteur's classical re- 

 searches on the relation between optical activity and 

 crystalline form. Much fault need not be found with this 

 book because it contains rather dogmatic statements of 

 debatable propositions, but we venture to think tlic 

 treatment of the subject too sketchy and superficial to 

 aflford much real help to the student. 



M. Monod's little Ijook relates only to the stereochem- 

 istry of carbon, and tlic isomerism of nitrogen compounds 

 is not referred to. Now this department of theoretical 

 chemistr>' is one which should be entered by the student 

 at a comparatively advanced stage of his progress, 

 when he is already familiar with the more important 

 facts upon which the theory is based. It seem- 

 doubtful, therefore, whether so scanty an outline as 

 this will supply what is wanted by students at this 

 stage. They will desire to be told not only tliat a certain 

 ' number of groupings are possible with a stated number of 

 carbon atoms, which is usually obvious enough, but they 

 will require to be told something of the secondary hypo- 

 , theses with which the fundamental idea has become 

 encrusted. Kor example, the union between two carbon 

 atoms joined by a single bond is shown (p. 17) to be 

 "mobile," that is, each carbon is supposed to be able to 

 rotate, together with its attached radicles, round the axis 

 joining the two carbons ; but the student is left at th.it 

 point to wonder why it should rotate at all. It is only . 

 much later (p. 63), in connection with the isomerism of i 

 fumaric and maleic acids, that reference is made to the | 

 doctrine of attractions between the radicles associated I 

 with carbon atoms adjacent to each other. In this case it 

 is not justifiable to say that the attraction of CO^ll for H 

 is C7'iiieii//y greater than that of CO^H for COJl or H : 

 for n. There is nothing ei'iden/ about the statement, 

 which is almost purely hypothetical, such evidence as | 

 docs exist tending almost as much one way as the other. ' 



Throughout the book the conventional tetrahedron is 

 the symbol used, and we have not been able to find any 

 account of \\ iinderlich's hypothesis as to the configur- 

 ation and union of carbon atoms, nor of Bacyer's strain 

 theory in the formation of closed chains, nor of any oilur 

 explanation of the way in which two carbons may unite 

 by double or triple bonds, and the consequences of sucli 

 union. 



The most inlercsting part of tlic hook is the hiiif 

 fourth section, which relates to the researches and in - 

 potheses of (iuye as to the relation between the rotatory 

 power of the substance and the masses of the radic les 

 attached to an asymmetric carbon in the molecule of an 

 optically acti\e compound. 



