37fr MM. Dumas and Lies-Bodarton the Preparation dfGalblum. 



Gahnite was obtaiued by placing a mixture of fluoride of alumi-- 

 nium and fluoride of zinc in vessels of iron, containing boracic 

 acid placed in a platinum tray. The Gahnite is deposited on 

 the various parts of the apparatus, in very brilliant regular octa- 

 hedra coloured by the iron. 



When the boracic acid is replaced by silicic acid, and volatile 

 fluorides employed, crystallized silicates may be obtained. In 

 this manner staurotide was obtained in form and in composition 

 like the natural mineral. It is also obtained by heating alumina 

 in a current of gaseous fluoride of silicon. The alumina becomes 

 changed into cruciform crystals which have the composition of 

 staurotide. 



Rutile was obtained by the decomposition of a fusible titanate, 

 more especially titanate of protoxide of tin, with silica. 



According to Lies-Bodart, the metal calcium is readily obtained 

 by the following method : — Equal equivalents of sodium and of 

 iodide of calcium are placed in a wrought-iron crucible provided 

 with a screw lid. The crucible is then fastened down and 

 heated gradually for an hour at a red heat, care being taken not 

 to pass or exceed this. When the crucible is cold, the metal ia_ 

 found on the surface. In one operation, 3 grammes of calcium 

 were obtained with 4 gramnies of sodium. 



The metal is dull in appearance, which arises from its being 

 covered by a thin layer of a blackish substance, believed by the 

 author to be a suboxide of calcium, and which is readily detached : 

 a surface freshly cut has a pale yellow colour with a reddish 

 reflexion. Calcium requires a red heat to burn in the air; once 

 inflamed, it burns with great brilhancy, projecting sparks. It 

 decomposes water at the ordinary temperature. 



Dumas* has confirmed this, but has found that the result is 

 only obtained when the action takes place in closed vessels. By 

 heating sodium with iodide of calcium at the ordinary pressure, 

 the first burns, and the latter remains unchanged. 



Brewster, more than thirty years ago, described the occurrence 

 of cavities and liquids in the crystals of various minerals. The 

 cavities in some cases were empty, in others contained air and one 

 or more liquids. They were mostly found in topaz, quartz, and 

 amethyst, but were met with in very many minerals, and among 

 others in diamonds. Frequently in one and the same cavity of 

 a quartz or topaz two liquids were found, one of which was 

 heavier than the other, and but little expansible; the other was 

 lighter, and extremely expansible. The first was doubtless water, 

 it had the refractive index of that substance. On opening the 



* Comptes RenduSj vol. xlviii. p. B75. 



