order to prevent loss by oxidation is held beneath the surface of the molten aluminium by tongs until it is melted. As regards the best contents of Mg for alloys designed for various uses, Klaudy states that a 2 to 5 % Mg alloy is best for wire-drawing; 5 to 8 % for rolling; 12 to 15% for casting, and that the average strength of a cast 10% Mg alloy is 20,000 Ib. per sq. inch. An alloy he recommends for aeroplane construction work has the following composition : Al 80 parts; Mg 12 parts; Cd 8 parts.
The Al Mg Cu alloys are stated to be useful for chemical work, as for example the alloy containing 96 % Al, 2 % Cu and 2 % Mg. This alloy is very dense, machines well, and has been used with success for the construction of a 3-in. flanged valve, designed for work with acetic acid.
As regards the methods of manufacture adopted for producing pure magnesium, it is known that before the war the Germans were manufacturing the metal by the electrolysis of fused " carnallite," a naturally occurring salt containing potassium and magnesium chlorides. The position at the commencement of the war was, therefore, that Germany had practically a monopoly of the manu- facture of magnesium, and supplied the whole world with its require- ments of the metal. It was only under the stress of war conditions that English and American manufacturers commenced to take an interest in this very interesting metal.
As regards America there were, in 1921, two plants at Niagara Falls producing magnesium, under the control of the American Magnesium Corporation, and there was also one at Rumford Falls, controlled by the Rumford Metal Co. The latter plant employed as raw material a pure magnesia obtained as by-product from some other process. The Dow Chemical Co. of Midland and the General Electric Co. of Schenectady are two other firms which produced magnesium in America during the war. Concerning the process of reduction or extraction used by the plants at Niagara Falls, very little information is available. There is no doubt, however, that the process used is an electrolytic one, and that the electrolysis takes place in a bath of fused chlorides with aluminium present when an alloy is desired. At Rumford Falls, where MgO is used as raw mate- rial, the method in fact is exactly similar to that used for the manu- facture of aluminium.
Quartz-Glass and Fused Silica Ware. This electric-furnace product has been manufactured since 1904 at Wallsend-on-Tyne by the Thermal Syndicate, and at Hanau in Germany by He- raeus. Quartz is an impure form of silicic acid (Si02) ; and quartz- glass is, therefore, a glass consisting chiefly of silicic acid, whereas ordinary glass contains silicic acid in combination with lime, soda, potash or lead. The great advantages of quartz-glass as compared with ordinary glass are that it has a much higher melting point and that it is not fractured by sudden changes of temperature. Other important properties are that it is neither hygroscopic nor soluble in acids, and that alkalies affect it less than ordinary glass except at the higher temperatures. It is, therefore, of great value for chemical and research work.
In the early days of the manufacture only tubes were made. The method of production was to embed a graphite rod in sand, and to heat this with a current of high amperage. A white opaque tube of quartz was obtained in this way, of much greater diameter than the graphite core. The opacity was due to the air entangled in the raw material, this air being imprisoned as minute air bubbles in the pasty mass when it softened under the application of heat. The latest method of overcoming this defect is to heat the fused tube a second time quickly up to 1800 C. by aid either of an oxyhydrogen flame or of the electric arc. The cellular structure then collapses, and a semi-translucent tube is obtained which is not only stronger but is a better conductor of heat than the original opaque tube. The highest grade of glass-sand and modern methods of blown-glass manufacture are now employed, with the aid of iron moulds similar in construction to those used for glass bottles, to produce any hollow kind of fused silica ware.
Sodium. The Castner cell and process for the production of metallic sodium by the electrolysis of fused sodium hydrate has been generally adopted.
In a recent American patent, No. 1,334,179 of March 1020, and assigned to the Dow Chemical Co., A. W. Smith and W. R Veazey, of Cleveland, proposed to substitute a mixture of 35-6 parts of sodium chloride and 64-4 parts of sodium carbonate for the more expensive sodium hydrate. This mixture melts at 600 C. and yields a product equal in quality and purity to the present commercial sodium.
application of electrolytic or electrothermal methods in connexion with the tin industry has been confined to the recovery of the metal from tin scrap and from the old tin cans found in the refuse of all large towns. At one time the electrolytic recovery of tin from these two sources became a branch industry of some importance; but these electrolytic methods of treating tin-scrap metal and refuse had in many places
been displaced by 1921 by newer methods, depending upon the use of liquid or gaseous chlorine. The electrolyte methods, however, continued to be carried on by some municipalities.
The alkaline process of electrolytic tin-stripping was patented first in the United Kingdom, by an Englishman named Beatson ; but the German firm, Th. Goldschmidt & Cie., of Essen, Germany, was the first to see and to turn to good account the possibilities of the process. This firm, by organizing the collection of the waste scrap in all countries and its transport on a large scale to their works at Essen, obtained at one time almost a monopoly of the raw material of the industry. The scrap, after cleaning and freeing from grease and fat, was employed as anode material in baths which contained a 10% sodium-hydrate solution as electrolyte. Under the influence of the current the tin was dissolved as sodium stannate, and was deposited at the cathode as metallic tin, with reformation of the sodium hydrate. The chief chemical, therefore, was continuously regenerated, and the only drawback of the process was that the solu- tion of the tin was not quite complete, and the iron-tin alloy, which existed on the plate under the coating of tin, was not dissolved by the sodium salt. The residual iron left in the vats still carried, there- fore, measurable and variable amounts of tin, which diminished its value from the steel-melters' point of view.
At one time before the war, the alkali process of tin-stripping was being worked at seven different centres in Europe and at one or two in America, and over 40,000 tons of tin scrap was treated annu- ally by the process. A plant which operated in Limehouse, London, was reported to be using the same process.
Electrolytic tin-stripping methods, which are based upon the use of ferric and stannic chlorides as solvent for the tin, have been patented and tried also upon a commercial scale. Their great advantage is that the solder and hard alloy of iron and tin, under the tin coating, is removed by the chloride treatment; and that only one-half the electric current required by the alkali process suffices to deposit the tin from the chloride electrolyte. The Bergsoe and Browne & Neil processes of tin-scrap treatment were the most notable examples of this method in the past. More recently, Walter and Lodge have patented the use of a stripping solution consisting of a 7 % solution of caustic soda or potash, with I % of stannous chloride, heated to l8oF. The scrap is placed in bags in a per- forated revolving drum, which is rotated or oscillated within the vat, and is divided into longitudinal compartments by the cathode plates which project into it internally. The method is protected by British patents Nos. 122,025 and 122,618 of 1918, and is reported, to have been operated in Birmingham.
Zinc. The many different processes which had been patented or experimented with, up to the year 1910, for the electric deposition of zinc from sulphate or chloride solutions of the metal paved the way for the improved methods and processes of the later period, and there were in 1921 many large plants in operation in America and Australia, producing electrolytic zinc upon an industrial scale. Success depends upon freeing the electrolyte supplied to the depositing vats from all impurities more electro-negative than zinc copper, cadmium, lead, anti- mony and arsenic. The presence of even very minute amounts of the two last-named impurities (arsenic and antimony) is found, in fact, to lead to low-current efficiencies. The non-recognition of this fact led to the failure of many of the electrolytic processes that were tried upon an industrial scale in the past. The other essential of success is to prevent " treeing " of the deposited zinc, since this leads to short-circuiting in the vats; and " treeing " has been overcome by stripping the cathodes every 48 hours, and by not attempting to form thick sheets of zinc.
The most modern and largest plant in which electrolytic zinc was being produced in 1921 was that erected in 1918 by the Anaconda Copper Co. at Great Falls, Mont., for recovery of the zinc from the complex zinc-lead ores of the Butte district, by a sulphate leach- ing process. The tank-house of this plant contains 864 vats, each 10 ft. long by 3 ft. wide by 5 ft. deep; and each vat will hold 28 anodes and 27 cathodes. The latter are of rolled sheet aluminium from which the deposited zinc can be stripped easily. The anodes are of chemical lead. The current for each unit of 144 cells is supplied by a rotary converter of 5,800 K.W. output, 10,000 amperes at 580 volts being required to run this number of cells. At full load the current density employed is 30 amp. per sq. ft. of cathode area, but 22 to 25 amp. yields the most satisfactory deposit.
Similar plants have been erected and operated at Park City, Utah, by the Judge Mining and Smelting Co. for treatment of the concentrates from a sulphide ore containing zinc, lead and silver; and at Trail, B.C., by the Consolidated Mining & Smelting Co. of Canada. This latter company claims to have been the first to put electrolytic slab zinc on the market at a cost which left a profit to the producer. The average composition produced at Trail, B.C., is Zn, 99-93%; FeO, -005%; Pb, -038%; Cd, -027%.
