5i6 



NATURE 



[October i, il 



likely to be effectual. An expenditure of one-fiftieth of 

 the cost of the recent epidemic would probably secure 

 the country from any such infliction in future. But we 

 must admit that without a somewhat strict supervision at 

 ports of entry during the period of prevalence in other 

 countries, and without provision for the segregation of 

 slight or suspected cases during that period, mere 

 notification would not be likely to put a stop to the 

 spread of influenza. The early cases are worth taking 

 a great deal of trouble to discover and isolate. When 

 once many cases have occurred in a locality, the 

 further progress of so protean a disease is difficult to 

 arrest. The best chance of averting an epidemic 

 must be sought in scrupulous care for early isolation, in 

 tracing the movements of travellers from infected towns, 

 and in the increased practice of ventilation in private 

 houses and in public gatherings. Like typhus, influenza 

 seems incapable of inflicting much damage except 

 through the medium of close, confined, and impure air, 

 and where measures of isolation and disinfection are 

 used it seldom spreads. But the infectious character of 

 influenza must be internationally recognized before pro- 

 tective regulations can achieve a full measure of success. 



R. Russell. 



GENERAL CHEMICAL MINERALOGY. 

 Allgemeine Cheitiische Mineralogie. Von Dr. C. Doelter, 

 O. Professor der Mineralogie an der K. K. Universitat 

 Graz. With 14 Figures in the Text. (Leipzig : W. 

 Engelmann, 1890.) 



MINERALOGY, at first purely descriptive, has been 

 raised to the dignity of an experimental science 

 by the application of the principles of chemistry and 

 physics. The writer of a mineralogical text-book is thus 

 met at the outset with the difficulty of deciding what 

 amount of knowledge of chemistry and physics to assume 

 in his reader. With regard to the chemical side at least, 

 the rule appears to be to assume that he knows very 

 little, and yet, somewhat inconsistently, to make the ex- 

 position of the atomic theory and the fundamental prin- 

 ciples of chemistry so brief as to be of little service to 

 one who has had no previous acquaintance with the 

 subject. 



The author of the present, in many respects useful and 

 suggestive, book follows the same lines. The whole 

 account of the fundamental chemical theories occupies 

 about ten pages of the introduction. The same fault will 

 be found in other parts of the book : e.g. it would be 

 difficult to say to what class of reader a large portion of 

 the chapter on chemical analysis would be useful. In 

 his endeavour to introduce as many extracts as possible 

 from the current literature of the subject, the author 

 allows himself in many places to become somewhat 

 sketchy. In spite of this, the book, with its wealth of 

 information upon points which have not hitherto found 

 a place in ordinary mineralogical text-books, will be 

 found to give a very good idea of the present state of 

 mineralogical science from a chemical point of view. 



The arrangement of the book is in seven sections, viz. 

 (i) introduction ; (2) chemical crystallography ; (3) che- 

 mical analysis of minerals ; (4) synthesis of minerals ; 

 (5) metamorphism of minerals ; (6) formation of minerals 

 NO. 1 144, VOL, 44] 



in nature ; (7) chemical composition and constitution ot 

 minerals. 



In the introduction, containing an account of the 

 atomic theory and its consequences, one or two sugges- 

 tive ideas will be found : e.g. the correspondence, pointed 

 out by Tschermak, between the chemical law of multiple 

 proportions and the crystallographic law of simple para- 

 meter ratios ; and also the analogy between the law of 

 constant proportion by weight and the fundamental crys- 

 tallographic law of constancy of angle. The subject of 

 chemical crystallography receives very full treatment. 

 Here the reader is initiated into the mysteries ot 

 chemical and physical isomerism, polymorphism, 

 enantiotropy, isomorphism, isodimorphism, isogonism, 

 morphotropy, &c. ; and if the perusal of this section,, 

 as well as of the last, on the constitution of minerals, 

 shall leave him with a rather confused and unfavourable 

 idea of the subject, the fault should perhaps be rather 

 attributed to the present imperfect state of our knowledge 

 than to the author. At present it is in most cases impos- 

 sible to say whether bodies are polymeric, metameric, or 

 chemical isomers. 



As regards isomorphism, if the formation of mixed 

 crystals is to remain the test, the original definition 

 of Mitscherlich must be modified to suit the fact 

 of the formation of mixed crystals from compounds 

 ot not precisely analogous chemical composition. 

 Thus, according to modern views, isomorphism is in 

 some degree to be deposed from its proud position as an 

 infallible guide to chemical composition. The insidious 

 nature of the attack upon this ancient stronghold of the 

 faith may be judged by a comparison of one of the latest 

 definitions of isomorphism with the original definition of 

 Mitscherlich. According to the latter, isomorphism is 

 the power which two or more compounds of analogous 

 chemical composition possess of crystallizing in the same 

 or similar crystalline forms, and of mixing in varying 

 proportions to form homogeneous crystals. The latest 

 definition is that bodies are isomorphous which, with for 

 the most part similar chemical composition, possess the 

 property of crystallizing in similar crystalline forms, and 

 of forming mixed crystals which morphologically and 

 physically graduate into each other. Such a change it is 

 expected would lead to a considerable simplification in 

 many of the formulas which have been made unnecessarily 

 complicated in order to comply with the requirements ot 

 Mitscherlich's definition. 



The section on chemical analysis of minerals is one ot 

 the least satisfactory in the book. Short summaries ot 

 analytical methods can be of little service to any class of 

 reader. Amongst matter which will not be generally 

 found in the ordinary chemical text-book, this section 

 contains some account of microchemical reactions, of the 

 methods for the mechanical separation of minerals, so as 

 to insure pure material for analysis, and directions for 

 the course of analysis to be pursued in the case of the 

 more important minerals. 



The important subject of mineral synthesis receives 

 more complete treatment than any other in the book. 

 The section contains general accounts of the various 

 methods for the artificial production of minerals by che- 

 mical reactions, fusion, sublimation, electrolysis, diffusion, 

 &c., with detailed descriptions of the apparatus required. 



