Notices respecting New Book*. 455 



has been one of the most prolific suggestions in organic chemistry 

 since the " benzene theory " of Kekule. The article concludes 

 with some suggested changes in the terminology of the subject 

 which chemists will do well to consider carefully whether they 

 adopt them or not. 



The next article demanding notice is that on Isomorphism by 

 Dr. Hutchinson, which extends to nearly 8 pages. The author 

 has found it necessary, in view of the development of the subject 

 since the time of Mitscherlich, to modify the definition of the term. 

 Dr. Hutchinson considers isomorphism to be " a part of that branch 

 of physical chemistry which studies the relations between the 

 chemical composition and crystalline form of bodies, and which 

 from a knowledge of the constitution and chemical properties of a 

 substance seeks to predict its system, form, and crystallographic 

 constants." The author justly points out that this final aim has 

 rarely been achieved as yet, and he then goes on to discuss the 

 relations between the chemical composition and crystalline form 

 under the three headings of Polymorphism, Morphotropy (includ- 

 ing Isomorphism), and Isogonism (" bodies not chemically related 

 possess the same form "). The article as a whole is a decidedly 

 valuable summary of existing knowledge with respect to a subject 

 which has hardly as yet received its proper share of attention. 



The article on Ketones by Dr. Japp displays this authors well- 

 known special knowledge of these interesting compounds. A 

 somewhat lengthy article on Lead is contributed by Mr. Muir, 

 and the same author writes on Magnesium, the Magnesium Group 

 of Elements, Manganese, and Mercury. The article on Metal- 

 lurgical Chemistry by Dr. Huntingdon is much too short, extending 

 over only 4 pages. Mr. Crookes discusses the Rare Metals in 

 some 8 or 9 pages profusely illustrated with maps of spectra. 

 This article, as might have been anticipated from its authorship, 

 is not only a masterly summary of our present knowledge — to 

 which Mr. Crookes has himself made such splendid contributions 

 — but it is equally valuable from its suggestiveness. The state at 

 which we have arrived appears to be this : — 



" We have, therefore, some thirty bodies of which the so-called rare 

 metals are composed, or, at least which they contain ; and a variety of 

 facts point to the conclusion that we have by no means come to the end. 

 Several even of the new bodies give signs of a capability of further 

 splitting up, if they are examined with sufficient nicety and persistence. 

 It is far from unlikely that when the various methods of research known 

 as fractionation have been more generally applied we may have to deal, 

 not with thirty, but with nearer sixty, unknown bodies." 



In answer to the question as to what these bodies into which 

 the rare earths have been resolved are the author goes on to say : — 



" Pending, therefore, the completion of a series of investigations, 

 chemical and optical, which will probably occupy several generations of 

 chemists, it may be safest to call these recentlv observed bodies not, as 



