MINERALOGY. 277 



ble to go into the subject here, but it may be mentioned as 

 a point of some interest that the varying amounts of water 

 obtained by analysis in the ordinary potash -mica are ex- 

 plained by the different degrees in which the potassium is re- 

 placed by basic hydrogen in the different cases. Streng has 

 made an extended examination of chabazite from different 

 localities both crystallographically and chemically, and in 

 the latter respect has arrived at a somewhat different view 

 of the composition from that previously held. He shows, 

 however, that between certain limits the composition of dif- 

 ferent varieties varies considerably. 



Rauff has investigated the mineral zancrinite by chemical 

 analysis, supplemented by the microscope, and concludes that 

 the carbonic acid present in it is really an original constitu- 

 ent, and not, as has sometimes been urged, a product of later 

 decomposition. A series of extended memoirs upon the min- 

 eralogy of Scotland have been published by Hecldle. They 

 cover a large range of subjects, and contain the results of 

 much original work, particularly in the way of chemical anal- 

 yses. Mallet has added an analysis to the few already ex- 

 isting of the Mexican selenide of bismuth, gitanajuatite, which 

 serves to establish its true composition beyond doubt. The 

 associated mineral silaonite, originally described as another 

 selenide of bismuth, has been proved by Bruns to be only a 

 mixture. 



The behavior of the natural sulphides with iodine and other 

 reagents is the subject of a memoir by Bolton. The reagents 

 employed were iodine, potassium iodide and citric acid, and 

 potassium bromide and citric acid. Ninety minerals were ex- 

 amined, and only nine resisted these methods of attack. 



ARTIFICIAL FORMATION OF MINERALS. 



The formation of mineral compounds by artificial means 

 a most important branch of the science has been much ex- 

 tended by recent researches. Fremy and Feil have found it 

 possible to form crystals of corundum of such a size as to be 

 suitable for use in watch-making. They obtained the best 

 results when a fusible aluminate was combined with a suit- 

 able silicate, and kept in crucibles at an extremely high tem- 

 perature for twenty days. The alumina is set free gradually 

 by this means, and forms crystals of true corundum. By the 



