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Alum

the name given to double salts of sulphate of aluminum with sulphates of potassium, sodium, ammonium, or of other monatomic metals, as silver, thallium cæsium, rubidium. They crystallize in octohedra. Potash alum, m, Al2K2 Al₂K2(SO4). +24H2O, is prepared by the decomposition of a shale containing iron pyrites. Alum has a sweet astringent taste, reddens litmus paper, and dissolves in its own weight of boiling water. Sodium alum is very soluble. Ammonia alum is often prepared by adding the ammonia liquor of gas-works instead of potash.

Alum is used in dyeing and in preparing skins, etc. Alum is used in medicine as an astringent in doses of 10 to 20 grains.

Ammonia alum, a mineral, called also tschermigite. Feather alum, a mineral, called also halotrichite. Iron alum, a mineral, called also halotrichite. Magnesia alum, alum, a mineral, called also pickeringite. Manganese alum, a mineral, in shipbuilding, especially for torpedocalled also apjohnite. Native alum, a boats. And as it is especially suitable

Aluminum has, in recent years, come into common use for culinary utensils and other domestic uses, and in manufactured articles where strength and lightness are requisites. It is especially valuable in the making of aeroplanes and automobiles. Not being acted upon by organic secretions, it is used for optical, surgical, and chemical instruments and apparatus. Aluminum leaf and wire may be employed with great advantage in place of silver leaf for decoration, or silver wire for embroidery. Of late it has come to be used price of copper, but, bulk for bulk, the was, weight for weight, three times the for cooking-vessels, efforts to cast it for pots and pans have often been made, but unsuccessfully till 1895 when aluminum was, weight for weight, three times the price of copper, but, bulk for bulk, the cheaper metal the expense for making industrial use of metal .

In 1855 Napoleon III. paid aluminum at Javel. Many other manufactories of aluminum were also started about the same time in France. In 1856, price of aluminum was reduced to less methods of production were used, the upward, and when in 1888 electrical Camden. In 1857, the price of aluminum was from $28 to $32 a pound. Between 1862 and 1877 it ranged from $12 upward, and when in 1888 electrical methods of production were used, the price of aluminum was reduced to less than $1. In recent years it has dropped to a quarter and even a fifth of that price.

The sources most used for the production of aluminum are bauxite, a mineral first found near Baux, but since then found in Styria in Austria, in Ireland, and in many places in the United States; and cryolite, found on the W. coast of Greenland. There is no other useful metal, iron not excepted, which is widely scattered over the earth and which occurs in such abundance. The value of the aluminum produced in the United States in 1918 was $41,159,000. The production of bauxite was 569,000 long tons, valued at $3,244,000. For occurrence and production in the United States, see BAUXITE.

Aluminum Alloys. - The aluminum bronzes, now becoming so generally introduced, are the alloys of aluminum and copper, in which the amount of copper considerably exceeds that of aluminum. bronzes consists in their non-corrosive The value of these aluminum properties and in their strength.