384 SCIENCE PROGRESS 



state is discussed at considerable length by A. H. Compton 

 {Jour. Frank. Inst. 185, 745, 191 8), who concludes, on the basis 

 of the Dulong- Petit law and the results of X-ray analysis, that 

 in the solid state the atoms are so intermingled that it is im- 

 possible to define particular molecules, each atom exerting an 

 equal attraction on all neighbouring atoms. From a con- 

 sideration of the relation between melting-point and " atomic 

 heat of formation," it is stated that in crystals atoms are held 

 together by forces analogous to those existing in chemical 

 molecules. 



In a theoretical paper A. C. Crehore (Phys. Rev. 10, 432, 

 1 91 6) derives mathematically the equilibrium conditions for 

 some types of space lattices, certain assumptions being made 

 regarding the type of motion and velocity of the electrons, and 

 applies the results to a number of cubic crystals. 



A partial elucidation of the structure of the garnet is given 

 by S. Nishikawa (Proc. Tokyo Math. Phys. Soc. (2), 9, 194, 

 191 7), and of lead, barium, and strontium nitrates by the same 

 author and K. Hudinuki (ibid. 197). Several substances have 

 been examined in the same way by F. M. Jaeger and H. Haga 

 (Proc. Akad. Wetensch. Amsterdam, 18, 1350, 1357, 191 6). 



Mixed Crystals. — H. R. Kruyt has continued his investiga- 

 tion of the three-phase (solid, liquid, gas) equilibrium in those 

 binary systems in which the two compounds form a continuous 

 series of mixed crystals. In an earlier paper (Proc. Akad. 

 Wetensch. Amsterdam, 12, 537, 1909) the various curves were 

 theoretically discussed, while later (ibid. 13, 206, 1910) the 

 system p-dichloro-benzene — p-dibromo-benzene was experi- 

 mentally investigated. Recently (ibid. 19, 439, 191 6) the system 

 iodine — bromine, which contains the compound IBr., probably 

 miscible in all proportions with its elements, has been examined 

 and a characteristic temperature-pressure curve for the co- 

 existence of three phases has been found. In another paper 

 (ibid. 19, 555, 191 7), however, it is shown that this type of 

 curve does not necessarily depend on the existence of solid 

 solution. 



C. Viola (Atti Real. Accad. Lincei (5), 25, ii. 285, 1916) 

 has carried out a crystallographic investigation of the mixed 

 crystals of magnesium and zinc sulphates, and concludes that 

 these are composed alternately of each salt and therefore differ 

 from solid solutions which are physical mixtures. 



