230 Intelligence and Miscellaneous Articles. 



white light, there will be seen ultimately, in the direction of each of 

 these axes, a brilliant orange spot traversed by a hyperbolic branch. 

 These expand to the right and left of the principal section in the 

 form of curved pencils, half violet and half dark blue, and divide the 

 field of the lamina into two regions, in which the purple tints gra- 

 dually become degraded on either side of their common limit. 



The dark tufts interrupted by the luminous spot are also fringed 

 towards the point with a little yellow and blue ; this coloration is 

 entirely local, and manifestly arises from the dispersion of the optical 

 axes corresponding with the different colours. This dispersion is, 

 in fact, pretty distinct in nitrate of strontia. 



These appearances, perfectly characteristic of the polychroism of 

 crystals with two optical axes, and absolutely identical with those 

 first observed by Brewster in Cordierite, found by Haidinger in an- 

 dalusite, and tolerably distinct in some varieties of epidote, are 

 manifested with much greater splendour in the large laminse which 

 may readily be prepared with nitrate of strontia. In their natural 

 state the colourless crystals exhibit nothing similar, and the optical 

 axes only become visible by means of polarized light. Other suit- 

 able colouring matters and other crystallized salts produce analogous 

 eflfects in various degrees. — Comptes Rendus, Jan. 23, 1854, p. 101. 



ON ALUMINIUM AND ITS COMPOUNDS. BY M. DEVILLE. 



It is known that Wiihler obtained the metal aluminium in the 

 state of a powder by treating the chloride with potassium. By a 

 suitable modification of Wohler's process, the decomposition of the 

 chloride of aluminium can be regulated so as to produce a tempera- 

 ture sufficient for the particles of the metal to agglomerate into 

 globules. If the mass composed of the metal and chloride of 

 sodium (sodium is preferable to potassium) is exposed to a bright 

 red heat in a porcelain crucible, the excess of chloride of aluminium 

 is expelled, and there is left a saline mass with an acid reaction in 

 which are disseminated more or less large globules of perfectly pure 

 aluminium. 



This metal is as white as silver, and in the highest degree mal- 

 leable and ductile. When wrought, however, it exhibits greater 

 resistance, and its tenacity probably approaches that of iron. It is 

 hardened by hammering, but reacquires its softness on being re- 

 heated. Its fusing-point differs but slightly from that of silver ; its 

 specific gravity =2"a6; it can be smelted and cast without being 

 perceptibly oxidized ; it is a good conductor of heat. It is not in 

 the least affected by moist or dry air, does not tarnish, but remains 

 bright by the side of zinc and tin freshly cut, which soon become 

 dull. Sulphuretted hydrogen has no action upon it, cold water does 

 not alter it, boiling water does not tarnish it. It is not acted upon 

 by nitric acid, weak or strong, or by weak sulphuric acid, employed 

 cold. Its true solvent is hydrochloric acid, with which it forms 



