-Recent Books
New Conceptions in Colloidal Chemistry. HERBERTFREUNDLICH, PFI.D., Professor a t the Kaiser Wilhelm Institute for Physical Chemistry, Berlm. E. P. Dutton and Company, New York. 1927. With 47 diagrams and 20 tables. vii 147 pages. 12.5 X 18.5 em. $2.00.
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This book contains the subject-matter of a series of lectures given by the author in the University of Minnesota during the summer of 1925. The title is iudicative of the nature of the contents; its purpose is set forth in the preface as follows: "Science consists in approximations. We first form a more or less rough and crude picture of the phenomena we are dealing with, and then draw it more exactly and with greater precision, as our knowledge grows. This development may be observed very clearly in capillary and colloidal chemistry. The general conceptions of adsorption, the electrical potential of surtaces, the state of aggregation and shape of particles, which conceptions were sufficient same years ago, had to be worked out in greater detail in order to account for the manifold new experimental results." The author has succeeded in correlating the recent experimental data concerning these topics, and has brought the generalizations together in s logical and pleasing manner. Other topics which have received similar treatment are: the rate of coagulation; the stability of hydrophilic sols; the extent and change of surface in colloidal systems; and photo-dichroism and similar phenomena. The hook is well written and the theoretical treatment has been developed with commendable fairness. Research workers and advanced students in colloid chemistry will find the hook stimu-
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lating as well as instructive. It can be read with profit by any one who has a fair knowledge of the literature of colloid chemistry, though from the standpoint of general information it can in no sense replace the other recent books by this author. The reviewer feels that this hook could well serve as the begiming of a series of books of the same general title, preferably by the same author, which would appear periodically, say, a t about three-year intervals. F. E. BARTELL
Lehrbuch der Enzyme. CARL OPPENmmx, with the collaboration of Richard Kuhn. Georg Thieme. Leip660 pp. 17 X 25 cm. zip, 1927. ix 18 figures. Unbound, 33 M.; bound, 36 M.
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This textbook represents an abridged form of the fifth edition of Oppenheimer's "Die Fennente and ihre Wirknngen." The same outline or arrangement of material was used in both instances and many sentences or paragraphs have been carried aver from the larger work into the Lehrbuch. Since the Latter appeared two years later than the first volume of Die Fermente, it follows that certain changes have been made in order to bring the Lehrbuch up to date. Because of the less extended treatment accorded each section in the Lehrbuch, the authors have been more didactic than was the case in organizing Die Ferment*. This may be of advantage to the student, since he is not left in doubt concerning the author's opinions and candusions. Oppenheimer has treated this complex subject under two major divisions, designated as I General. and I1 S~ecial. In the first part the enzymes are considered more or less collectively. The descriptive
