The nature of a patent is discussed with an actual patent as an illustration, patent publications are listed and the methods of making.a search described. Three chapters are devoted to secondary publications, abstract journals, index and review serials, bibliographies, handbooks, encyclopedias,monographs, and texthwks. The student is told what is in these and how to work through them to the original sources. The third section is the practical part. After some information about technical libraries and their use, a series of problems is given. These are t o he assigned t o students as laboratory experiments to he reported on a t the next meeting of the class. They begin with simple questions and lead up t o the preparation of a bibliography on such things as artificial silk, aluminum alloys, and protective coatings. The book is well adapted for class instruction, for which it is intended, and will be useful t o chemists who have had inadequate instruction in library methods, and that means the most of us. E. Emsr REm TEW JotlNs HOPYlNS U N r V B R S I N
HOMEWOOD. RALTrMORB, MD.
Salts, Acids, and Bases: Electrolytes: Stereohemistry. PAULWALDEN,Professor of Chemistry, University of Rostock. McGraw-Hill Book Company, Inc., New York City, 1929. iii 397 pp. 26 figures, 1 plate. 15 X 23 cm. $4.00.
+
No less than the author, the translator of these "Baker" lectures a t Cornell, is t o be congratulated on a workmanlike performance. Dr. I,. F. Audrieth has produced an eminently readable English version containing few of those grotesque constructions into which inexperienced or careless translators easily fall. Professor Walden has treated three separate fields of chemical study which have especially engaged his interest and to two of which he has made distinguished mntrihutions. The history of the con-
cepts acid, base, and salt is almost coextensive with the history of chemistry, a t least until about a hundred years ago, and to follow with the author the fluctuating meanings of these words over the murse of centuries is to sympathize much more intelligently with the perplexities of the alchemist and the iatrochemist, pioneers in the chemical jungle. Such a survey gives us also an historical background which we sorely need today when the air is full of proposals for redefinition of some of these most fundamental terms. With regard t o the naming of bases and acids, the author discusses critically the proposals of Franklin, Lewis, Brtinsted, Germann, and others, and his conclusion is embodied in the following query (p. 159): "Would it not be better, in place of the more or less sweeping generalizations, to retain the old-established names and concepts with their hydrogen and hydroxyl ions based upon the behavior of aqueous or water-like electrolytic solutions, and to introduce special terms for the exceptional cases dealing with new-types of solvents?" In the sections that follow, Walden's own workron the physical properties of non-aqueous solutions is reviewed. Among the very numerous interesting results reported the following may< he especially noted. When two salts such as NRCI and NR%H.Cl are compared in a variety of solvents, it is found that the apparent dissociation is nearly the same in water and in alcohol, but that in acetone, methylene chloride, chloroform, and ethylene chloride, the former salt appears to he respectively, 10, 170, 800 and several thousand times as much dissociated as the latter. This is correlated with the behavior of the strongest acids, which all show practically complete dkociation in water or alcohol, but gradually change into weaker and weaker electrolytes as Less and less basic solvents are used. An illuminating discussion of the famous Walden Inversion concludes the book. This volume is to be recam-
