Geological Society. 461 



Trevor and the author are joint editors, and the present volume is 

 issued by the publishers of the journal. 



The work consists of a general discussion, without mathematics, 

 of the conditions of equilibrium of chemical mixtures, in which the 

 amount of any component, the temperature, and the pressure are 

 considered as variable. Van 't Hoff, in his ' Studies in Chemical 

 Dynamics,' and others have examined a few such cases of equili- 

 brium quantitatively, while Roozeboom has done much experi- 

 mental work of a more qualitative character ; but, so far as we 

 are aware, no attempt has been made until now to classify the 

 phenomena. 



The author defines a phase as a mass of uniform concentration, 

 and its components as the substances of independently variable 

 concentration contained in it. For a mixture of phases in equili- 

 brium every phase will furnish an equation involving functions of 

 its components together with the temperature and pressure. The 

 number of equations will thus be equal to the number of phases, 

 while the number of independent variables will be n-\-2 if the 

 mixture contains n components. A system consisting of n+2 

 phases will thus give as many equations as there are variables ; 

 such a system can only exist at a single temperature and pressure 

 and is called non-variant. An equilibrium mixture of ice, water, 

 and steam belongs to this type. If the number of phases is only 

 n+ 1 the system is monovariant, and is fully determined by the 

 specification of one of its variables ; with n phases the system 

 is divariant, and so on. The scope of the present volume is 

 limited to non-, mono-, and di-variant systems, with at most four 

 components ; and in the discussion of changes of equilibrium the 

 general theorem of Le Chatelier is made use of, namely, that 

 whenever a system is disturbed from without, it adjusts itself to 

 the new conditions by the occurrence of a corresponding reverse 

 change within itself ; for example, an increase of external pressure 

 will cause an increase in the amount of the denser phases. The 

 author demonstrates the extreme usefulness of this theorem in 

 predicting the effect of any given change. 



The value of Mr. Bancroft's treatise lies not so much in the fact 

 that it presents the results of a large amount of experimental 

 work in physical chemistry, but rather that it indicates a scientific 

 method of classifying all such work ; he has, in fact, taken the first 

 step towards the formation of order out of chaos in this department 

 of science. J. L. H. 



LXI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 396.] 



March 24th, 1897.— Dr. Henry Hicks, F.R.S., President, in the Chair. 



HPHE following communications were read : — 

 -*■ 1. ' Notes on some Volcanic and other Rocks which occur near 

 the Baluchistan-Afghan Frontier, between Chaman and Persia.' 

 Phil Mag. S. 5. Vol. 43. No. 265. June 1897. 2 M 



