RECENT ADVANCES IN SCIENCE 385 



In another paper (ibid.(s), 26, i. 195, 191 7), by a mathematical 

 treatment, the equilibrium conditions between mixed crystals 

 and the amorphous phase are examined. The mean growths 

 perpendicular to the crystal faces are found to vary as the 

 capillary constants, and hence the general form is ultimately 

 the mean of the forms of pure crystals of the substances forming 

 the mixed crystals, due regard being paid to the proportions 

 in which they are present. Curie's law regarding surface energy 

 is stated to hold for mixed crystals. Isomorphism of crystals 

 is held to depend upon the mean miscibility as well as similarity 

 of structure and volume. 



L. Vegard and H. Schjelderup (Pkys. Zeit. 18, 93, I 9 l 7> 

 Jour. Chem. Soc. 112, ii. 243, 191 7), from an X-ray examination 

 of mixed crystals of potassium chloride and bromide and of 

 potassium and ammonium bromides, maintain that mixed 

 crystals are not composed of alternate layers, but that the 

 atoms are arranged in lattices similar to those of the compo- 

 nents, the main difference being that in the first case some 

 of those points which in the lattice of the simple salt KC1 

 would be occupied by chlorine atoms, are now occupied, in 

 the mixed crystal, by bromine atoms, with analogous results 

 in the second case. The unit of the lattice has necessarily a 

 different volume from that of the lattices of the components. 



G. Tammann (Nachr. K. Ges. Wiss. Gottingen, 191 6, 199, 

 Jour. Chem. Soc. 112, ii. 448, 191 7) has investigated the effect, 

 on binary mixed crystals, of reagents which attack one of the 

 components, and has found that the action does not vary 

 proportionately to the amount of attackable constituent. There 

 are certain limits of composition between which the resistance 

 to attack is great, and these limits have been determined, for 

 a number of reagents, in the systems copper-gold and silver- 

 gold. 



Physical Properties. — P. W. Bridgman (Amer. Jour. Sci. 

 (4) 45, 243, 191 8) has published the results of some in- 

 teresting work on the elastic behaviour of crystals. Circular 

 cylinders of various materials were pierced with cylindrical 

 holes concentric with the outer surface, and the phenomena 

 accompanying the failure of these cavities under high pressure 

 was observed. The method of failure in such materials as 

 quartz, felspar, tourmaline, and so forth, is totally different 

 from that observed in the case of metals, as, instead of the 



