180 Aluminium. 



part, by weight, of pure alumina, are dissolved in an equal 

 weight of water, and precipitated by a concentrated and boiling 

 solution of acetate of lead in slight excess; and the smallest 

 possible quantity of tartaric acid, is added to the liquor which 

 is separated by decantation, to prevent the precipitation of 

 alumina. The acetate of alumina is then supersaturated with 

 ammonia, and the ammoniacal solution, after being treated with 

 hydrosulphuret of ammonia, in a closed vessel, is placed in a 

 stove having a temperature of from 122° to 140° Fahr. : this 

 determines the precipitation of the sulphurets of iron and lead, 

 which are removed, first by decantation, and then by filtering 

 — but without washing the filters. The clear and slightly yellow 

 liquor, which consists of acetate and tartrate of alumina com- 

 bined with ammonia, and some hydrosulphuret of ammonia, 

 is rapidly evaporated and carbonized in an earthen crucible. 

 The residual mixture of alumina and carbon is made into a paste 

 with oil, and strongly calcined to expel the sulphur — due to 

 a little sulphuric acid which remains in the alumina, the whole 

 of it not having been separated by the acetate of lead. 



To obtain pure chloride, of aluminium. — Some of the mixture 

 of alumina and carbon, just mentioned, is introduced into a 

 porcelain tube that has been fitted with another tube, and is 

 heated to redness in a current of dry chlorine. Chloride of 

 aluminium sublimes, and is removed from the tubes in compact 

 masses, which are composed of very beautiful crystals, that 

 are either colourless or slightly tinged with yellow. If, 

 however, from the impurity of the materials, this chloride is 

 not found to be quite pure, it is heated with nails or iron- 

 turnings, in an earthen or cast-iron vessel, which, when the 

 permanent gases have passed off, is closed : after which, 

 the heat being continued, a slight pressure results, that causes 

 the chloride of aluminium to melt and come in contact with the 

 iron. This changes the volatile perchloride of that metal into 

 the jprofochloride, which is comparatively fixed : and the chloride 

 of aluminium, completely purified, crystallizes in the vessel itself 

 in large transparent and colourless prisms : and a distillation in 

 hydrogen finishes the process. 



To obtain the sodium. — Its preparation is founded on the 

 reaction of an alkaline carbonate on carbon ; and carbonate of 

 soda, wood charcoal, and carbonate of lime are required in the 

 following proportions — 



Carbonate of soda 71 7 



Wood charcoal 1 75 



Chalk 108 



1000 



