22 SCIENCE PROGRESS 



difficult to explain on the immiscibility hypothesis, on account 

 of the possible formation of mixtures analogous to emulsions. 

 Rather are such occurrences to be explained by movements 

 in the partly consolidated magma due to " the action of 

 warping stresses, torsional stresses, and in some cases shearing 

 stresses acting at the appropriate stage of crystallisation." 

 In this way, such a structure as the primary banding in the 

 Duluth gabbro may have originated. 



The relationships between a-spodumene, the natural mineral, 

 and the /3-form, into which the a-variety is transformed on 

 heating to i,ooo°C., have been further investigated by F. 

 Meissner {Zeit. anorg. Chem., 110, 187, 1920). The view of 

 R.Ballo and E. Dittler {ibid., 76, 39, 1912) that the transforma- 

 tion is irreversible is confirmed by thermal analyses and by 

 density determinations on material annealed at high tempera- 

 tures. The identity of the 7-variety, formed by the crystallisa- 

 tion of the molten salt, with the yS-variety is indicated by a 

 comparison of the optical properties. The behaviour of the 

 felspars on prolonged heating at temperatures just below the 

 melting-points has been examined by H. Leitmeier {ibid., 105, 

 69, 191 8). It is found that the amount of alkali lost by 

 volatilisation is extremely small, even after seventy- two hours' 

 heating. 



In continuation of his work on the problem of the formation 

 of such magmatic felspathoids as nosean, hauyne, and so 

 forth, P. Niggli {ibid., 106, 126, 1919) has investigated the 

 system NaaCOg — KgCOg — CaCOg between the temperatures 

 600° C. and 1,000° C, and under a pressure of i atmosphere 

 of carbon dioxide. The binary system, sodium carbonate — 

 potassium carbonate, and that composed of the double salts of 

 each of these with calcium carbonate belong to Roozeboom's Type 

 III, and form a continuous series of solid solutions. In the ternary 

 system are found two series of mixed crystals, one in which 

 there is constantly one molecule of calcium carbonate, that is, 

 mixed crystals of the double salts mentioned above, and another 

 composed of mixed crystals of the three carbonates in varying 

 proportions. The latter are apparently isomorphous mixtures 

 of the alkali carbonates with a small proportion of the calcium 

 salt. Data for the ternary system, sodium carbonate - 

 calcium carbonate - sodium chloride, are also given. 



Amongst other papers on mineral syntheses, one, dealing 

 with the hydrothermal formation of silicates, by W. J. Miiller 

 and J. Koenigsberger {ibid., 104, i, 191 8), may be noted. 

 Discussions, from the chemico-geological point of view, of the 

 occurrence of various minerals in some of the German salt- 

 deposits have been published by M. Rozsa {ibid., 101, 279, 

 191 7 ; 105, 167, 1919 ; Cent. Min., 36, 191 7 ; 121, 191 8). 



