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NEW BOOKS
which rise, but the namedoes not adequately express the great source of energy in the avalanche at the base of the cloud. The data are microphonic, seismologic, and astronomic, in addition to the narrative of major events and a few notes on the temperatures. The observed speeds of flow of the nudes ardentbes ranged from 10 to 33 meters per second. There are some electrical charges from the clouds, and “flashing arcs” are described as possibly light reflected from a sound wave-front. One physicochemical hypothesis is presented by the author with the frank remark that it may be “outrageous,”-namely, that at depths some igneous magma may be in a vapor phase because of excess heat. The latest statement of expert opinion on this is by Fenner (in Economic Geologu, volume 30, pp. 929-930, 1935) and is unfavorable t o the idea, showing also that high pressures may develop from dissolved gases without having the magma itself become gaseous. The general reader will find interest in the section (pp. 8 to 12) on the diagnosis and prediction of volcanic eruption, and in the many excellent photographs. FRAXK F. GROUT.
Das Kristallzeichnen auf Grundlage der stereographischen Projektion. By H. TERTSCH. 23 x 15 cm.; iv and38 pp.; 34 figs. Wien: Julius Springer, 1935. Price: 3.60 RM. The orthodox methods of drawing crystals from a stereographic projection are described with special emphasis on their application to the study of habit. Successive sections deal with the drawing of a plan on the plane of projection and with representation in parallel perspective on an arbitrary plane, the true habit being obtained by the use of measured central distances. A further section describes the drawiQgof twin crystals. The writing is clear and concise, but a few of the more complicated figures might have been reproduced with advantage pn a larger scale.
F. C. PHILLIPS. Wassersto~-lonenkonzentration( p ~ ) .By H. JORGENSEN, with an introduction by S. P. L. Sorensen. 15 x 22 cm.; 264 pp. Dresden: Theodor Steinkopff. Price: paper, 15 RM; bound, 16 RM. In recent years there have appeared both in the English and in the German languages, a number of excellent books dealing with the determination and applications of hydrogen-ion concentrations; the author of the book under review has nevertheless written another, apparently a t the request of the publishers to fill a gap in their series of scientific monographs. Nearly half of the book, 114 out of 246 pages of text, is devoted t o a consideration of the fundamental principles involved in the determination of pH, and the theoretical aspects of electrode potentials, buffer solutions, and electrolytic equilibria are discussed in a concise but adequate manner. The treatment of acids and bases is particularly interesting, since the author adopts throughout the modern viewpoint which regards acids as yielding and bases as accepting protons, respectively. The next section of the book, 52 pages in length, consists of a review of the niethods of measuring pH; the author does not intend this t o be complete, for the reader is referred t o other treatises for further practical details. Nevertheless the methods of using the hydrogen and quinhydrone electrodes are described in sufficient detail, but the account of the glass electrode is little more than an indication of how i t can be used. Colorimetric methods for determining pH, which either do or do not involve the use of buffer solutions, are described, although the simple “drop-ratio” method of Gillespie is not mentioned. The last portion of the text, entitled “Technischer Teil,” occupies some seventy pages, and in i t are described sixty-two examples of the importance of measurements
