SI 4 Intelligence and Miscella?ieous Articles. 



Tills Avas several times prepared; and the proportions followed in 

 the greater number of experiments were — 



Alumina 600 grs. 



Magnesia 3-00 



Fused boracic acid 6'00 



Green oxide of chromium .... O'lO to 0"15 gr. 



By heating this mixture, well-defined and brilhant crystals of a 

 rose-red colour were obtained, the form of which was easily distin- 

 guished by a glass. They were regular octahedrons, truncated on 

 the twelve edges, constituting the-octa'edre emargine oiHauy. Quartz 

 was readily scratched bjj^ the mass ; by treating this with hydro- 

 chloric acid repeatedly, the crystals were left unacted upon and se- 

 parate ; their density was 3'548, while that of the natural spinelle 

 varies from 3"523 to 3'585. 



By analysis the author found these crystals to yield — 



Alumina 71-9 



Magnesia 27'3 



Oxide of chromium . . 1*2 



100-4 



the formula being Al- 0^ MgO, which agrees with the statement 

 already made as to the composition of the rose spinelle. Various 

 other crystals of this substance when submitted to analysis showed 

 their agreement in composition with the natural minerals. — Ann, de 

 Ch. et de Phys., Fevrier 1848. 



ON THE CRYSTALLINE FORM OF METALLIC ZINC. 



M. J. Nickles observes, that the crystalline form of pure zinc has 

 already been described by M. Noeggerath {Pnggendorff's Annalen, 

 vol. xxxix. p. 324), who found this metal in prisms with hexagonal 

 bases. Zinc, antimony and arsenic, are then the only crystalline 

 metals, the form of which does not belong to the regular system. 

 The metals of the magnesiari series do however crystallize in this 

 system ; and if zinc has hitherto formed an exception, it may be 

 hoped that dimorphism will eventually connect this metal with 

 the group of metals to which it belongs by its chemical properties ; 

 and the author mentions that he is enabled to state this fact already 

 with respect to some crystals of pure zinc prepared by M. Favre 

 according to the process of M. Jacquelain. 



These crystals are very distinct pentagonal dodecahedrons, very 

 similar to the form of iron pyrites and gray cobalt. 



This example of dimorphism is not unique among metals. Prof. 

 Miller, who has examined the crystalline form of tin, has shown that 

 it crystallizes in the system of the prism with a square base. M. 

 Frankcnheim has observed the same metal crystallized in cubes ; and 

 very lately M. G. Rose {Poggendorff's Annalen, vol. Iv. p. 329) 

 has announced that platina and iridium are isodimorphous. Both 

 crystallize in the rhombohedric and cubic system. 



