Alumina.

By reference to the analysis of the ore made at Apothecaries' Hall, it will be seen to contain four substances—scheelite, alumina, potash, and silica. I have already shown and also verified by repeated experiments that the scheelite can be extracted at a very trifling cost, and as the scheelite is not chemically combined with the silica, alumina, and potash, the residue, after its extraction, will contain these substances in the proportion of alumina 19 02, potash 1150, the rest being silica, which means quartz. Alumina is used in the Arts principally as an alloy; it occurs plentifully in nature, but generally in such a state of combination as to render its extraction extremely difficult and expensive, hence its great cost, the metal being worth about £4000 per ton. Up to the present time Greenland is the only part of the world where the ore of aluminum is found, called cryolite.

As to the general uses and importance of the metal aluminum, I will give a few extracts bearing on the subject :—Cassells' Popular Educator, Vol II., pages 65 and 116, Vol II., page 214.—"The metal aluminum is white, resembling silver. The pure metal has lately been found in quantities available for manufacturing purposes, and from its extreme lightness, its freedom from tarnishing, and its sonorousness, it page 10 promises to become a most useful product. It is obtained from the silicate of alumina, but more economically from cryolite found in Greenland."

Year Book of Facts, 1865, page 178 :—"A new method for obtaining metallic aluminum has just been discovered by Mr. Corbilli. He takes a quantity of silica containing aluminum (i.e.—in the state in which it is found in the scheelite lode), and dissolves say 100 grammes in six times its weight of concentrated sulphuric, nitric, or hydrochloric acid. The solution is then allowed to stand and afterwards decanted. The residue is first dried and then heated to 450 or 500 degrees centigrade, after which it is mixed with 200 grammes of prussiate of potash, which may be increased or diminished according to the quantity of silica. To this mixture 150 grammes of common salt are added. The whole is then put into a crucible and heated until the mixture becomes white. When cold a button of pure aluminum is found at the bottom of the crucible."

Various methods are adopted in the production of the metal, but the one just mentioned appears to be the most economical I have seen described. M. Dumas, in the Comptes Rendus, details another system lately discovered by a Paris chemist, but like all the rest, although effective, it is very complicated.

Seeing that the ore can be got at a very trifling cost, and the metal being as valuable as silver, the cost of extraction must be enormous, but as experiments are being made in all the laboratories of Europe, it is generally believed some cheap process will be hit upon. Two alloys of aluminum have been manufactured at Newcastle, viz.: copper 95, aluminum 5, and copper 92½, and aluminum 7½, called aluminum bronze, and from its appearance it cannot be told from gold, even by experts. Vast quantities of cheap jewellery are being made from it. The hardness is quite equal to the best brass and 44 times more rigid, and it shows excellent casting qualities and behaves well under the file. It can be drawn out to a very fine wire, which, on account of its extreme lightness, is preferable to silver. No metal equals it for the manufacture of astronomical instruments, as it is not affected by oxygen and very slightly by acids.

Mr. C. M. White, in the Journal of the Society of Arts, observes : "The discovery of an easy method of procuring this noble metal from the silicate, would open the way to fame and fortune for the discoverer. Notwithstanding its present high price its consumption is steadily increasing."