558 SCIENCE PROGRESS 



the nickel structure ; those with above 93 per cent, chromium 

 have the chromium structure, while the intermediate alloys 

 show both. The system copper-manganese is similar, both 

 lattices being detectable in alloys containing from 60 to 90 per 

 cent, manganese. In the systems copper-nickel and copper- 

 gold there is apparently no break, the change being linear. 

 Iridosmine has been shown by G. Aminoff and G. Phragmen 

 {Zeit. Krysi., 56, 510, 1921) to be composed of a centred 

 hexagonal lattice. 



The structures of the oxides of calcium, magnesium, cadmium, 

 and nickel have been examined by W. P. Davey and E. O. 

 Hoffman {Phys. Rev., 15, 133, 1920), who deduce a face-centred 

 cube arrangement for both the metal and oxygen atoms in each 

 case. E. Schiebold {Zeit. Kryst., 36, 430, 192 1) has also 

 examined magnesia, but in the form of the natural mineral 

 periclase. G. Aminoff (ibid., 56, 495, 192 1) confirms the 

 results of W. L. Bragg (Phil. Mag., 39, 647, 1919) with reference 

 to zincite. In addition to X-ray analj-ses of the minerals, an 

 attempt is made by G. Aminoff (Geol. Foren. Fork. Stockholm, 

 41, 407, 1919 ; Zeit. Kryst., 66, 506, 1921) to ascribe space 

 groups to brucite and pyrochroite. In another paper by the 

 same author (Geol. Foren. Forh. Stockholm, 42, 211, 1920) the 

 structures of the minerals parisite and synchisite are considered. 



The structures of a series of analogous complex compounds, 

 such as ammonium platinichloride, ammonium silicofluoride, 

 etc., have been determined by some American workers. The 

 first-mentioned has been shown by R. W. G. Wyckofif and 

 E. Posnjak (Journ. Amer. Chem. Soc, 43, 2292, 1921) to be 

 analogous to fluorspar, the ammonium atoms replacing the 

 chlorine and the platinum and fluorine together replacing the 

 calcium. Similarly, ammonium silicofluoride has been investi- 

 gated by R. M. Bozorth (ibid.,^, 1066, 1922), who finds that the 

 structure is similar to that of the platinichloride. R. W. G. 

 Wyckoff has examined the series of compounds of the general 

 formula NiX2.6NH3 (ibid., 44, 1239, 1922), where X repre- 

 sents the halogen atoms, as well as the compound of similar 

 formula, where X represents NO3 (ibid., 44, 1260, 1922). The 

 same author (ibid., 44, 1944, 1922) has shown silver molybdate 

 to be analogous to spinel. Wyckolf (Amer. Journ. Sci., (5), 

 4, 188, 1922) has also investigated hexahydrated zinc bromide 

 and has assigned a specific space group to it as well as to acid 

 sodium acetate (ibid., (5), 4, 193, 1922). 



The nitrates of lead, barium, strontium, and calcium have 

 been examined by L. Vegard (Zeit. Physik., 9, 292, 1922), who 

 finds that the metals are arranged in a face-centred cube with 

 the three oxygens and the nitrogen at the four cube corners 

 surrounded by four atoms of metal so that the symmetry is 



