Mineralogy. 179 



The aluminium, as thus formed, is a gray powder, very similar to the 

 powder of platinum. It is generally in small scales or spangles of a metal- 

 lic lustre, and on some occasions small, slightly coherent, spongy masses 

 were observed, which in some places had a tin- white metallic lustre. The 

 same appearance was rendered perfectly distinct by pressure on steel, or in 

 an agate mortar. The metallic aspect is therefore complete, and in this re- 

 spect aluminium differs from silicium. In its fused state it is a conductor 

 of electricity, but it does not possess this property in the form of powder. 

 Dr Wohler remarks, that metallic iron in the form of fine powder is a non- 

 conductor of electricity, and that, therefore, the conducting power of metals 

 is connected with their form. 



Aluminium requires for fusion a temperature above that at which cast- 

 iron is liquefied. When heated to redness in the air, it takes fire and 

 burns with vivid light, yielding aluminous earth, considerably hard, and 

 of a white colour. Sprinkled in powder in the flame of a candle, brilliant 

 sparks are emitted like those given off during the combustion of iron in oxy- 

 gen gas. When heated to redness in a vessel of pure oxygen, it burns with 

 an exceedingly vivid light, and emission of intense heat. The resulting alu- 

 mina is partially vitrified, of a yellowish colour, and equal in hardness to 

 the native crystallized aluminous earth, the corundum. It not only scratches 

 glass but even cuts it. It was remarked that the inner surface of the glass 

 in contact with the aluminium during its combustion was half melted and 

 brown, an appearance which Dr Wohler ascribes to the reduction of sili- 

 cium. Heated to near redness in an atmosphere of chlorine it takes fire, 

 and the chloride of aluminium is sublimed. 



Aluminium is not oxidized by water at common temperatures, nor is its 

 lustre tarnished by lying in water during its evaporation. On heating the 

 water to near its boiling point, oxidation of the metals commences, with 

 feeble disengagement of hydrogen gas, which continues even long after cool- 

 ing, but at length wholly ceases. The oxidation, however, is very slow by 

 this means, and even after continued ebullition the smallest particles of 

 aluminium appear to have suffered scarcely any change. 



Aluminium is not attacked by concentrated sulphuric or nitric acid at 

 common temperatures. In the former, by the aid of heat, it is rapidly dis- 

 solved with disengagement of sulphurous acid gas. In dilute muriatic and 

 sulphuric acid, it is dissolved with evolution of hydrogen gas. In order to 

 prove that the aluminium was free from potassium, the solution in sulphu- 

 ric acid was slowly evaporated, but no trace of alum appeared. 



Aluminium is easily and completely dissolved even by a dilute solution 

 of potash with disengagement of hydrogen. Even ammonia dissolves the 

 metal with evolution- of hydrogen gas ; and it is remarkable what a large 

 quantity of alumina is held in solution under these circumstances. 



III. NATURAL HISTORY. 

 MINERALOGY. 



25. Datholite or Prismatic Dystome Spar. — Mr Bauersachs, lecturer 

 on mineralogy in the Royal Mining-School of Clausthal, in the Uarz, has 

 found this mineral in the Waschgrund Valley, near St Andreasberg, in 



