Notices respecting New Books. 139 



reviewer's point of view. But in this fourth volume there are 



certain long articles on special subjects by well-known authorities, 



which form a most valuable feature of the work, and to which 



attention may be directed. Thus, instead of the separate articles 



on electricity, light, heat, &c, which appeared in the old dictionary, 



we have one comprehensive article on Physical Methods used in 



Chemistry, which occupies no less than 100 pa^es and is divided 



into the fourteen sections : — Capillarity, Crystal lographic Methods 



(references only), Dialysis and Diffusion, Dynamical Methods 



(references only), Electrical Methods, Ereezing-points of Solutions 



(references only), Optical Methods, Osmotic Pressure (references 



only), Photographic Methods (references only), Specific Heats of 



Solids (references only), Thermal Methods, Vapour Pressures of 



Solutions (references only), Viscosity of Liquids, Volume Changes 



(references only). In cases where references only are given, it is 



because the section forms the subject of a special article elsewhere 



in the work. As a guarantee of soundness of treatment we need 



only mention the names of the contributors. Thus, Prof. Ostvvald 



is responsible for the section on electrical methods (46 pages), 



Prof. Hartley writes on optical methods (spectroscopic methods), 



Mr. George Gladstone the section on refraction and dispersion, 



and the editor (Mr. Muir) on polariscopic methods. Dr. Capstick 



contributes the sections on capillarity and viscosity. The section 



on thermal methods is also written by Mr. Muir. Taking it as a 



whole this article on Physical Methods is perhaps one of the most 



valuable in the Di2tiouary ; with the references and the original 



communications it constitutes a compact little monograph on 



Physical Chemistry, and those who have followed the developments 



of science since the time of the old Watts' Dictionary, cannot but 



be struck by the vast encroachment of Physics upon Chemistry, to 



the great advantage of both sciences. 



The article on Photographic Chemistry is by Prof. Meldola and 

 is compressed into about 5 pages ; Dr. Halliburton contributes 15 

 pages of most valuable information on Proteids ; Mr. O'Sullivan 

 writes on Starch, and also a long article (35 pages) on Sugar, in 

 which the enormous development in this branch of organic 

 chemistry, due chiefly to the researches of Emil Fischer, is very 

 well summarized and set forth. The article on Solutions is 

 divided into two sections — the first, by Prof. Arrhenius, representing 

 the views of those who hold to the physical theory, and the second, 

 by Prof. S. U. Pickering as the representative of the so called 

 " hydrate" theory. It is interesting to compare the views of the 

 two authors. Arrhenius sets out with the definition : — " A 

 solution is a homogeneous mixture of two or more bodies in the 

 liquid state." Pickering states : — "The view that hydrates exist 

 in aqueous solutions, and analogous compounds in non-aqueous 

 solutions, is one that has long been held by many chemists ; it is 

 only in the last few years, however, that the hydrate or association 

 theory has assumed a precise form, and that definite experimental 



