178 Scientific Intelligence. 



gas was afterwards displaced by dry and pure hydrogen. At common tem- 

 peratures the chloride of aluminium does not act on sulphuretted hydro- 

 gen but at the subliming point of the former the new compound is form- 

 ed, and collects in the neck of the retort. It is found partly in very white, 

 transparent, crystalline scales of a mother-of-pearl lustre, and partly as a 

 white, fused, brittle mass. It absorbs moisture rapidly from the air, and 

 at the same time emits a strong odour of sulphuretted hydrogen. Heated 

 in a glass tube, it is sublimed, but also undergoes partial decomposition, 

 emitting from thirty to forty times its volume of sulphuretted hydrogen 

 gas. From this circumstance it is obvious that the compound contains hy- 

 drogen as well as sulphur. 



When thrown into water it is decomposed with the same violence as the 

 chloride of aluminium; but a large quantity of sulphuretted hydrogen is 

 set free, and the solution is rendered turbid by separation of sulphur. By 

 performing this experiment in a glass tube over mercury, it was found 

 that no other gas but sulphuretted hydrogen is disengaged. By the action 

 of pure ammonia in water, alumina is precipitated, and a solution of the 

 muriate and hydrosulphuret of ammonia generated. 



24. Metallic Aluminium. — The preparation of this metal depends on the 

 decomposition of the chloride of aluminium by potassium, and on the pro- 

 perty of aluminium of not being oxidized by the action of cold water. Po- 

 tassium acts on the chloride of aluminium by aid of a moderate elevation 

 of temperature ; but the action is so violent, attended with disengagement 

 of intense heat and light, that a small quantity of the materials is destruc- 

 tive to tubes of glass. Dr Wohler succeeded in conducting the decompo- 

 sition in a platinum crucible, retaining the cover in its place by a piece of 

 wire. The heat emitted at the moment of the reduction was such that the 

 crucible, though but gently heated externally, became suddenly red-hot 

 from the caloric evolved during the change. The platinum is scarcely at- 

 tacked during the process ; but to prevent the possibility of error from this 

 source, the reduction was effected in a crucible of porcelain. The potas- 

 sium employed for the purpose should be quite free from carbon ; and the 

 largest quantity operated on at a time was about the size of ten peas. The 

 heat was applied by means of a spirit-lamp, and continued until the decom- 

 position was effected. The proportion of the materials should be carefully 

 arranged. The potassium should be in such quantity as to prevent any of 

 the chloride of aluminium from subliming during the decomposition, but 

 at the same time not so great as to render the reduced mass alkaline. The 

 matter contained in the crucible at the close of the operation is in general 

 completely fused, and of a dark-gray colour. When quite cold, the cruci- 

 ble is put into a large glass full of water, in which the saline mass is dis- 

 solved, with slight disengagement of hydrogen, of an offensive odour; and 

 a gray powder separates, which, on close inspection, especially in sunshine, 

 is found to consist solely of minute scales of metal. After being well wash- 

 ed with cold water, it is pure aluminium. The solution is neutral, and 

 contains a quantity of alumina, owing to a combination- being formed be- 

 tween chloride of potassium and chloride of aluminium. 



3 



