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tions, while graduate students will find that the book is very useful in giving them a reasonably complete survey of the subject. L. H. REYERSON.
VerSffentlichungen aus dem Kaiser Wilhelm-Institut ftlr Silikatforschung in BerlinDahlem. Edited by WILHELMEITEL. Vol. VI. 21 x 29 cm.; 234 pp. Brunswick: Fried. Vieweg und Sohn, 1934. Price: 28 RM. The Institute, under the direction of Dr. Wilhelm Eitel, continues to be very active in research, and the sixth volume of its collected papers contains much that is of scientific interest. Several investigations by H. E. Schwiete and H. Elsner von Gronow and colleagues deal with calcareous cements. Crystals from a Portland cement kiln in which small additions of fluorspar were made to the charge, and identified as alite, proved on analysis t o consist of tricalcium silicate holding 4.5 per cent of tricalcium aluminate in solid solution; the fact that such solubility occurs was confirmed by x-ray examination, the lines of the compound being clearly discernible, but disappearing on heating the clinker. The specific heats of the principal compounds present in Portland cement have been determined from 20°C. to 15OO0C., these data being required for the calculation of the heats of reaction in the kiln, Several other thermochemical investigations in this field have been completed, covering both the compounds present in clinker and those formed by hydration. A study of the development of heat during the setting of aluminous cement leads t o the conclusion that the process is purely colloidal and is governed by the pH value, an increase in this value accelerating setting, whilst a diminution retards it. This conclusion requires t o be controlled by other methods, such as microscopical and x-ray examination. A similar study of the setting of Portland cement also lays stress on gel formation as an essential part of the process. The papers on glass include a long review of the constitution of glass by W. Weyl, in which the subject is reviewed as a whole, as well as an experimental investigation in which glasses were prepared under high oxygen pressure, with the object of retaining in solution the higher oxides which ordinarily dissociate. Alkali lead glass in this way forms plumbates, which evolve oxygen when the glass is fused under reduced pressure. Manganese may also be retained as the higher oxide, so that under pressure a deep violet glass has been prepared, containing only 0.1 per cent MnO. A series of studies of the flow of glass in various machine processes for the production of bottles and other objects is remarkable for the very beautiful series of photographs taken by the Schlieren method. As usual, the volume contains accounts of several improvements in technique, which may be of interest to workers in other fields than that of the silicates. C . H. DESCH. T h e Design and Use of Instruments and Accurate Mechanism (Underlying Principles). By T. N. WHITFIHEAD.279 pp.; 85 figs. New York: The Macmillan Co., 1934. The book is written for the designers of accurate scientific instruments such as, for example, comparators. But the discussion covers much more than this field. The author deals with the fundamental principles covering design and the use of the resulting devices. He therefore deals with the theory of errors of observation from the standpoint of the instrument and from the standpoint of the human nature of the observer. He admits the utility of mathematics in the expression of physical phenomena, but warns that the use of mathematics must be tempered by independent check of the physical facts. The aim in writing the book has been “to concentrate on those parts of the subject which seem to call for revision and with which me-
