GEOPHYSICAL LABORATORY. 149 



indirect results of steam explosions without evidence of temperatures higher 

 than red heat. It is suggested that, inasmuch as Lassen Peak lies in a region 

 of considerable rainfall, the magma beneath the volcano carries a large per- 

 centage of water in solution, which is necessarily discharged during crystalliza- 

 tion with enormous local increase of pressure. It is believed that this is the 

 only mechanism hitherto studied through which sudden developments of 

 extreme pressure are possible in a cooling system. (See No. 439.) 



(471) The analytical expression of the results of the theory of space-groups. Ralph W. G. 

 Wyckoff. Publication No. 318, Carnegie Institution of Washington. 



All of the ways in which atoms can be arranged in space so that their 

 aggregate will possess one of the groups of symmetry properties observed in 

 crystals can be obtained from the theory of space-groups. Thus, in giving a 

 knowledge of all possible atomic arrangements in a crystal in advance of 

 detailed experimentation, this theory enters directly into the determination 

 of the structures of crystals through X-ray diffraction effects. 



The purpose of this book is to put the results of space-group theory into 

 a form immediately usable to the crystal analyst. As originally stated, the 

 theory concerned itself primarily with the different possible ways of spacially 

 distributing the elements of symmetry characteristic of crystals. For the 

 calculation of the X-ray diffraction effects to be expected from a grouping of 

 atoms, however, the coordinate positions of the atoms contained within a 

 unit cell of the crystal are desired. In the tables which constitute the major 

 portion of this book, the coordinates of the equivalent points (as positions 

 for chemically like atoms) are given for each of the 230 space-groups. Gen- 

 erally equivalent positions are obtained by operating upon any point within 

 the unit cell of a space-group by the characteristic elements of symmetry; the 

 special cases arise when the number of equivalent points is reduced through 

 their lying in one or more elements of symmetry. Not only are the general 

 positions stated, but the physically much more important special cases have 

 all been expressed in detail. A complete analytical expression is thus attained 

 in a form directly applicable to processes of crystal-structure determination. 



Because a brief account of the nature of the space-groups is not available 

 to English readers, a short discussion precedes the principal tabulations, which, 

 it is hoped, will somewhat fill this gap. 



(475) Solubility and decomposition in complex systems. George W. Morey. J. Soe\ Glass 

 Technology, 6, 20-29. 1922. 



The decomposition by water of glass and ceramic wares is a phenomenon 

 of great practical importance, primarily because the tendency toward such 

 decomposition is one of the factors which sets a limit in certain directions on 

 the compositions which we may employ. In this paper decomposition is dis- 

 cussed from the point of view of the phase rule and illustrated by comparison 

 with the complex systems H 2 0-K 2 0-Cr0 3 and H 2 0-K 2 0-Si0 2 . It is em- 

 phasized that the action of water on complex silicate mixtures, whether crys- 

 talline or wholly or in part glassy, is one of decomposition; and the results 

 of experiments to determine the relative fitness of such mixtures to withstand 

 the action of water or solutions should not be confused with the results of 

 true solubility determinations. The results obtained by tests as ordinarily 

 carried out represent the rates of decomposition, and because such rates are 

 profoundly affected by experimental conditions great care must be exercised 

 in specifying all of these conditions and in maintaining them constant. 



