Intelligence and Miscellaneous Articles. 247 



temperature of which is somewhat lower than that of the porcelain 

 furnace. When large quantities of alumina, magnesia and silica, 

 were exposed for several days uninterruptedly to the constant tem- 

 perature of this furnace, he obtained spinelle in octohedra of such 

 size, that they could be readily distinguished with the naked eye, 

 and their angles measured. They all consisted of perfectly trans- 

 parent octohedra, the twelve edges of which were truncated. The 

 facets of some of the octohedra were between three and four milli- 

 metres in breadth. 



M. Ebelmen has also produced zinc-spinelle or Gahnite. This 

 mineral, as found in nature, is always coloured brown or green by 

 peroxide of iron. M. Ebelmen obtained artificial Gahnite in a 

 perfectly transparent and colourless state. When oxide of chrome 

 was added to it, beautiful ruby-red octohedra with rhombic dodeca- 

 hedral facets of from two to three millimetres were obtained. 



The specific gravity of pure artificial Gahnite is 4*58, that of the 

 native mineral 4-23 to 4-70. The hardness of the former is the 

 same as that of the latter ; both scratch quartz readily. On com- 

 paring the density and the atomic weight of the aluminates of zinc 

 and magnesia, their atomic volume is found to be exactly the same ; 

 thus, that of the magnesian spinelle is 25*2, and that of pure Gahnite 

 25-1. 



M. Ebelmen also obtained chromites of zinc and magnesia, 

 i. e. compounds of sesquioxide of chromium Cr'^ O^ with bases RO, 

 which belong to the spinelle series. These, with the protochromite 

 of iron, which has been already described by the author in his first 

 memoir, show clearly that the native chromate of iron belongs to 

 the same family. 



The author also procured the ferrite of zinc, Fe^ O', ZnO ; it cry- 

 stallizes in black strongly sparkling octohedra, which yield a black 

 powder. They were not attacked by dilute acids, but dissolved in 

 concentrated hydrochloric acid. Their density is 5' 132. The 

 author concludes from the existence of this compound, that Frank- 

 linite is identical with it. 



The two following compounds are new, and of very great interest : 

 1, may neso -borate of chrome; and 2, per-magneso-borate of iron, 

 which the author regards as compounds of oxide of chrome and per- 

 oxide of iron, with tribasic borate of magnesia BO^.SMgO. This 

 borate BO-' + 3MgO is produced by the long-continued action of a 

 very high temperature upon the borate of magnesia with excess of 

 acid, and forms to a certain extent the mother-ley, out of which the 

 two above-described compounds crystallized. 



By the aid of boracic acid as a solvent, Ebelmen has also obtained 

 some silicates which were infusible per se at the furnace heat. In 

 this way he procured the silicate of magnesia MgO, SiO in perfectly 

 formed crystals, the angles of which could be measured, and the 

 measurements of which showed that they were identical with the 

 transparent Peridote of mineralogists. The bisilicate MgO, 2(SiO) 

 was obtained in long, beautifully white, pearly prisms, which exhi- 

 bited the cleavage of pyroxene. The corresponding zinc compounds 

 were also obtained in crystals. 



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