isotopes. Numerous examples are cited where the radio-elements are employed as indicators in analytical chemistry, in electrochemistry, in colloid chemistry, in the determination of powder surface, in inorganic preparations, in technology, physics, and physiology. The group of volatile hydrides (part 11) is treated under the following heads: Classification of the Hydrides; Preparation of Volatile Hvdrides of the H e a w Metals; Comparison of the Constants of the Volatile Hydrides: Comparison of the Volatile ~ y d i i d e s with other Volatile Compounds. The Natural System of the Chemical Elements (part 111) has the following three chapters: Periodic and Non-Periodic Properties of the Elements; Isotopes, Definition of the Concepts "Chemical Element," "Simple Element," "Complex Element;" The Number of Chemical Elements. This is a most interesting and suggestive book and is a notahle contribution to modern chemical theory. The translation has been excellently done. JAMES M. BBLL
since the book first appeared in its original form. The book is not recommended in general t o physicists but should find a place in an introductory and historic treatment of thermionics quite readable by high-school teachers of science and professional people who do not care t o go into the subject too deeply. There are a few mistakes and the careless use of mathematical equations may cause annoyance t o others than mathematicians or physicists, who are already accustomed t o these formulae. The book gives a very good picture of the development of thermionic phenomena. References are numerous and i t gives the impression of being written by one who is a scholar in the subject. The hook is not as rigorous, complete, or so mathematical as is Richardson's "Emission of Electricity from Hot Bodies," from which much of the material was taken. C. H. K U N ~ M A N
Pundamentals of Daiq Science. AssoCXATESoI. LOREA. RDGERS. American Chemical Society Monograph, No. 41. Chemical Catalog Company, N. Y., 1928. 543 pp. 31 figures. 15 X 22.5 Thermionic Phenomena. ?3ucam BLOCH. cm. $5.50. Mdtre de Conf6rences A la Facult6 der This comprehensive monograph repreSciences, Paris. Translated by J. R. sents the joint effort of no Less than twentyClark, MSc., F. Inst. P. E. P. Dutton & Co., New York City. x 145 pp. eight contributors. I t covers an extensive field in an orderly and systematic manner. 24 figures. 12 X 18.5 cm. $2.50. I n fact, its coherence and uniformity of Bloch's book on thermionic emission style as a manuscript is remarkable in view was probably of far more value as a "Conof the large number of individuals who ferences Rapports" a t the time it first contributed t o it. As a source of carefully appeared than it is today in the form of a selected facts gleaned from an extensive translation by Clark, as no reference is literature, it constitutes the most useful made in this book t o work done since 1920. and authentic document in its field of subThe last chapter of eighteen pages de- ject-matter. voted t o the application does not do iusThe monograph is divided into four tie to this field, as well as being difficult parts, each of which is further subdivided to follow. Probably no other single phe- into rhxptera. 1':rrL I , the conrtituents of nomenon has been more carefully studied milk, includei fire clnplers on the rornpuand generally applied in this decade than sition of milk and milk products, proteins thermionic emission. I t is a phase of one of milk, milk fat, pigments of milk, and of our largest industries-the radio indus- lactose. I n Part 11, the physical chemtry-which has grown up in this country istry of milk and milk products are in-
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