REVIEWS 489 



The Cbemical Examination 0! Water, Sewage, Foods, and other Substances. 



By J. E. Purvis, M.A., and T. R. Hodgson, M.A. Second and 

 enlarged Edition. [Pp. v + 346.] (Cambridge University Press, 1922. 

 Price 20s. net.) 



The first edition of this book is too well known to those interested in the 

 subject with which it deals to require any detailed description or commenda- 

 tion. In the new edition the book has been enlarged to the extent of over 

 100 pages. Nearly one-third of the volume is devoted to water, sewage, 

 and effluents, together with an increased number of typical analyses, which 

 should materially assist students in interpreting their analytical results ; 

 due attention is also given to the composition of sea water and its influence 

 upon the decomposition of sewage, a subject to which one of the authors 

 has devoted special study. New chapters dealing with the analysis of meat 

 extracts and products and with toxicology have been added ; the latter, as 

 stated by the authors, is put forward merely as a basis upon which a student 

 can work, and with the small amount of space devoted to it this is all that 

 can be claimed for it. For the rest, the book has been brought up to date in 

 a manner calculated to ensure its continued and well-merited success. 



Physico-chemical Problems relating to the Soil. A General Discussion held 

 by the Faraday Society. Reprinted from the Transactions of the 

 Faraday Society. Vol. xvii. Part 2, 1922, [Pp. 217-369.] (Price 

 los. 6d. net.) 



The Faraday Society has for some years followed the excellent practice of 

 holding General Discussions, at which papers, followed by discussion, are 

 presented on some aspect of Scientific Work coming within the purview of 

 the Society. The volume before us contains the proceedings of the twenty- 

 ninth of these meetings, and will be welcomed by all agricultural scientists. 

 There are at the present time very few branches of science unrepresented 

 in agricultural research, and the sixteen papers in this volume afford a good 

 idea of the progress already made, and the difficulties still to be overcome, 

 in our knowledge of the physico-chemical properties of the soil. 



The papers are grouped into five sections : Introduction, and general 

 papers, (2) Soil Moisture, (3) Organic Constituents of Soil, (4) Adsorption 

 Phenomena, (5) Colloidal Phenomena. That these divisions should be 

 regarded, in the main, as only a convenient way of grouping the papers for 

 the purpose of discussion, appears from the general survey of the subject 

 contributed by Dr. Russell. The soil is a system made up of mineral frag- 

 ments of all sizes, organic matter derived from past generations of plants 

 and animals, and moisture containing a number of substances in solution. 

 Some of the constituents of this system have marked colloidal properties, 

 and the presence of micro-organisms and the constantly fluctuating meteoro- 

 logical conditions introduce additional complexities. The soil investigator, 

 therefore, is faced by the problem of disentangling one or two factors from 

 a large number of interdependent ones ; he also has the further difficulty 

 that many of his problems are not necessarily made easier of solution by 

 replacing the soil by a simpler material, such as china-clay, o-wdng to the 

 degree of artificiality then introduced. This is clearly brought out in the 

 discussions, especially those following sections 3, 4 and 5, in which Dr. 

 W. R. Ormandy took a prominent part. These discussions largely dealt 

 with the effects of the clay fraction and the organic material in soil, and 

 one of the merits of Dr. Ormandy's critical comments was to focus attention 

 on some problems where a comparison of soil with substances such as china- 

 clay would be very desirable. A large amount of information has been 

 accumulated on the behaviour of clays used in the ceramic industry, and 

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