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960 patented and operated. The Schoop, Garuti, and Schukert cells were the best known of these. The first-named used sulphuric acid, while the remaining two employed caustic potash as electrolyte; the power consumption being 5-9 and 4-1 K.W.-hrs. respectively per cubic metre of the mixed gases.

In recent years, however, oxygen has been more economically obtained by the fractional distillation of liquid air, which can now be produced very cheaply; and hydrogen is obtained either from electrolytic alkali cells (as a waste product), or from blue water gas, by improvements of the old iron-contact process. By means of this, the carbon monoxide is first oxidized to C02 and is then removed from the gas mixture by absorption. The electrolytic production of hydrogen and oxygen is, therefore, now carried on in only a few localities, and for the few industries where both gases are required for immediate use in their relative combining proportions, as in the oxyhydrogen blowpipe.

Ozone. Since most of the early patents for ozone apparatus have lapsed by efflux of time, the general type of apparatus for the production of ozonized air, as placed on the market in 1921 has been standardized.

Ozonizers now usually consist of an inner cylinder of sheet copper or aluminium, connected to the high-tension side of the transformer and well insulated, and an outer metal cylinder which is connected to the casing of the ozonizer, and is kept at zero or earth-potential. The two cylinders are separated by a glass tube through which the air is passed, and the silent discharge takes place in the annular air- space between the two metal sheets. The outer sheet of metal is water-cooled, and thick glass windows at each end of the ozonizer tube enable the operator to see if the discharge through the air-gap is occurring in a proper manner. Alternating currents with fre- quencies up to 60 cycles are employed for these installations ; and the practical limit of E.M.F. has been found to be 10,000 to 12,000 volts.

Ozonized air has been employed for bleaching wax, textiles, paper- pulp and sponges; for the sterilization of air and food; and also for the acceleration of the drying and hardening processes in paints and varnishes, and for the rapid oxidation of oils.

Organic Products. It is difficult to obtain any information as to the extent to which electrolytic methods have been and are being applied in 1921 outside the laboratory in the field of organic chemistry; but there is reason to believe that in Germany considerable progress had been made in this direction, and that not only bromoform and iodoform but also anthraquinone and other organic products have been produced electrolytically.

Phosphorus. At one time the electrothermal process for the production of phosphorus from bone-ash was being employed at Oldbury, near Birmingham, and at Niagara Falls, and an output of 30 tons per month was reported to have been attained. The bone-ash was mixed with silicic acid (sand) and carbon, and the mixture was then heated to between 1300 and i5ooC. The phosphorus commenced to distil over at nsoC. and was all expelled from the mixture before a temperature of i45oC. was reached. According to Hempel, this method of manufacture had also been used in Germany, gas-tight iron cylinders lined with fire-clay being used as the furnaces in which the raw materials were heated. The use of silicic acid (or sand) to produce a calcium-silicate slag, it must be noted, is only practic- able with methods of reducing calcium phosphate which render this slag quite fluid, a result that can be attained only by aid of electric heat. Molten calcium silicate is also very corrosive, and the advantage of the internal system of heating is that the outer walls of the furnace can be artificially cooled, and a layer of cold slag can be formed to protect the refractory lining from the action of the slag.

A process very similar to that described above, for the manu- facture of phosphorus, was brought out in- America and patented some years ago in the name of Machalske. The furnace used for operating this process possessed an internal chamber, measuring 12 in. x 18 in. and was provided with a carbon bottom, sides of calcined magnesia, and a cover of fire-clay and red brick. Two electrodes, each 8 ft. in length by 4 in. in diameter, passed through holes in the cover. With electric power at 3 cents per e.h.p.-hr., Machalske claimed that yellow phosphorus could be produced by this method at a total cost of 7 cents per pound.

' From 80 % to 92 % of the phosphorus can be recovered by this method of manufacture; the balance remains in the furnace or retort as calcium silico-phosphate, and it cannot be expelled by any increase of the temperature.

II. ELECTROMETALLURGY

Aluminium. There were no discoveries or marked advances during the period 1910-20 in the development of new sources of aluminium, and the mineral bauxite remains the chief raw material of the industry. The increased demand for bauxite, however, has led to several new deposits being opened up and worked, and although none of these equal in purity the French bauxite deposits, the mineral has been found to be much more widely distributed over the world than was at one time supposed. With the aim of reducing the cost, numerous attempts have been made to dispense with the preliminary purification of the alumina (see 1.767-770) and to operate the baths with the raw bauxite, but these so far have not proved successful. In time this im- provement in the electrolytic process and reduction in cost of aluminium manufacture will no doubt be achieved.

The world's production of bauxite in recent years is given in Table I, which is taken from a pamphlet published in 1921 by the Imperial Resources Bureau. As regards alternative sources of supply, silicate of aluminium or clay is one of the most widely dis- tributed materials which occur in the crust of the earth. Weaver, in a recent Canadian patent (No. 190,054 of 1919), proposes toopenup this source of aluminium and its salts by treating the clay with chlorine in the presence of carbon. This leads to the formation of A1C1 3, S1CJ4 and CO, and with cheap supplies of liquid chlorine the method might be practicable. The chlorides are separated, and the metal is extracted by the electrolytic method described below. Whether this suggested process of using A1C1 3 in place of Al 2 Os as raw material for the aluminium industry will prove successful remains for the future to disclose.

Production and Output. The electrolytic process by which aluminium is produced from alumina, as worked in 1921, differed but little from that by which Heroult, at Neuhausen in Switzerland, and Hall, at New Kensington in America, first started the manufacture upon an industrial scale in 1889. The production, however, is now concentrated in the hands of a small group of powerful companies.

As regards the growth of the industry, the figures in Table II, taken from the pamphlet already referred to, indicate very clearly the remarkable expansion which has occurred in the manufacture during the period 1910-20. Compared with the figures compiled by J. B. C. Kershaw some years previously for the period 1893-9, the expansion of the industry becomes even more striking:

1893

1894

1895

1896

1897

1898

1899

Total World Output (tons)

713

1,057

1,129

i. 755

3,327

3,953

5459

In twenty years, therefore, the world's output of aluminium had increased from 5,000 to 150,000 tons, and the metal had come to rank 4th in the list of nonferrous metals, when judged by the standard of consumption ; for only copper, zinc and lead are employed in larger amounts in the arts and industries. The remarkable in- crease in production which marked the war period was of course due to war requirements; aluminium being used in enormous amounts not only in the powdered form for paints, and as an ingredient of certain forms of explosive (such as " ammonal "), and of pyro- technical materials, but also being employed, either as pure metal or in the alloyed state, for the construction of airships, aeroplanes, motor-cars, fuses, bombs, radiators and many forms of measuring instruments. The close of the war occasioned, therefore, a very considerable drop in the demand for the metal but there was little doubt that later the demand for aluminium in the arts and in- dustries would more than absorb the production of the increased plant.

As regards the localities and works where aluminium is now pro- duced, these are in every case operated by water-power, and the names of the companies and locations of the works are as follows:

United Kingdom. British Aluminium Co. Foyers and Kinlochleven, Scotland (Stang-

fjord, Vigelands, Norway). Aluminium Corporation Ltd. Dolgarrog, North Wales.

France.

Soc. Electrometallurgique francaise. Le Praz, Gardanne. Compagnie des Produits chemiques d'Alais. Calypso, St. Jean de

Maurienne, St. Felix.

Switzerland, Germany and A ustria. Aluminium Industrie Aktien-Gesellschaft. Neuhausen, Rheinfelden,

Lend Gastein.

United States of America and Canada. Aluminium Co. of America. Niagara Falls, Massena, Shawinigan

Falls.

Italy and Norway also possess aluminium works, and during t war two or three factories were started in the highlands of Bavaria for the production of the metal, by the Allgemeine Elektricitats Gesellschaft, of Berlin. The figures given in Table I show that during the last year of the war Germany produced 25,000 tons of aluminium, and was second only to the United States in her output