Avsa 16, 1897.] 



SCmNGE. 



625 



though, micas generally give lower values than 

 the true on account of their crystal habit. For 

 example, Lepidolite 2.9 (2.8-2.9), biotite 2.9 

 (2.7-3.1), muscovite 3. (2. 76-3.), phlogopite 2.9 

 (2.78-2.85). 



In spite of these slight deviations, which un- 

 dermine one's faith in the accuracy of the book, 

 there is little doubt that the tables will prove 

 serviceable to the practical worker who wishes 

 to gain at a glance the approximate values of 

 the substance under investigation. 



The typography of the book is good, the type 

 is clear, and the matter is well spaced. An es- 

 pecially attractive feature is the size, which is 

 adapted to the collecting bag or pocket. The 

 few instruments required, the use of the exter- 

 nal and physical properties only, the notes on 

 the paragenesis, and the great number of 

 rarer minerals, will make it serviceable alike to 

 the field geologist, the mining engineer and the 

 teacher. 



E. B. Mathews. 



Traits Slementaire de mScanique chimique, fondie 

 sur la fhermodynamique. P. Dtjhem. Paris, 

 A. Hermann. 1897. Vol. I. Large octavo. 

 Pp. viii+299. Price, 10 francs. 

 The object of this book is to give a consistent, 

 coherent account of the mathematical theory of 

 the changes in physical state and chemical 

 constitution, as obtained by an application of 

 thermodynamics. This would be valuable even 

 if badly done, since the mathematical treat- 

 ment of physical chemistry in book form is 

 painfully deficient in comparison with the ex- 

 haustive handling of the experimental side of 

 the subject by Ostwald. This particular book 

 is doubly valuable because it not only gives us 

 the mathematical development of the subject, 

 but presents it in a masterly way. 



Duhem begins with a short sketch of the ana- 

 lytical methods to be used, and then develops the 

 fundamental principles of thermodynamics, tak- 

 ing up in order the conservation of energy, the 

 first law of thermochemistry, the theorem of 

 Carnot-Clausius and the absolute temperature, 

 the entropy and the thermodynamic potential, 

 the general equations of thermodynamics, the 

 application of the thermodynamic potential to 

 systems at constant pressure or constant vol- 



ume, perfect gases, isothermal displacement of 

 equilibrium, heat effects, adiabatic displace- 

 ment of equilibrium and the change of the 

 equilibrium with the temperature. The re- 

 marks on the accuracy of Hess's law, page 49, 

 are especially worth reading because the points 

 raised are usually overlooked in the statement 

 of the theorem. 



The second part of the volume — devoted to 

 false equilibria and explosions — is even more 

 interesting than the first part because the point 

 of view is less familiar. Duhem has been 

 troubled like many others by the fact that in 

 certain cases there was a state of equilibrium 

 whea the theory, as formulated, said that this 

 was impossible. Gibbs showed that many of 

 the diflBculties could be removed by the assump- 

 tion that the surface of a phase was in a dif- 

 ferent state from the interior — in other words, 

 by the theory of capillarity. Duhem attempts 

 to carry this farther by introducing the notion 

 of viscosity or of false equilibrium. His idea 

 can best be understood by an analogy from 

 mechanics. Suppose we have a body on an in- 

 clined plane. In an ideal state of things where 

 there is no friction the body is not in equilib- 

 rium and will slide down the inclined plane. 

 In the world as it is we can not get rid of fric- 

 tion entirely and the body will remain stationary 

 on the plane, provided the pitch is not too great. 

 Similarly, if there were no passive resistance to 

 change, water vapor and a mixture of hydrogen 

 and oxygen in the proportions in which they 

 combine to form water should yield the same 

 system under the same conditions. At low 

 temperatures this is not the case experimentally, 

 so far as we now know ; so that it is natural to 

 follow out the analogy and to say that in the 

 actual chemical world there is a chemical fric- 

 tion or chemical viscosity and that states of 

 equilibrium are thus possible which could not 

 occur in a system where there were no passive 

 resistances to change. 



Duhem now attributes to capillary phenom- 

 ena the behavior of supercooled vapors and 

 superheated liquids, and he is inclined to group 

 under this head supercooled solutions, super- 

 saturated solutions and some theoretically un- 

 stable solid allotropic forms, classifying under 

 false equilibria hydrogen and oxygen, liquid 



