262 



SCIENCE. 



[Vol. XIII. No. 322 



sessed of the idea, that, if suitable means were discovered, it would 

 be possible to reduce the sodium and potassium compounds at a 

 much lower temperature by bringing the carbon into intimate con- 

 tact with the alkalies in a molten condition. If six molecules of 

 the hydrated oxide of sodium, commonly called caustic soda, be 

 added to one molecule of carbon, it will yield, when heated to a 

 high temperature, two molecules of carbonate of soda, three mole- 

 cules of hydrogen, and one molecule of sodium, — 



6 Na HO -f- C2 = 2 Na^CO., + 3 H^ + Na^ , — 

 and the reduction will take place in an atmosphere of hydrogen, 

 provided that a sufficiently intimate contact can be secured between 

 the carbon and the alkali. Mr. Castner's process to attain this 

 end, arrived at after a couple of years of patient experiment, is 

 partly mechanical and partly chemical. He prepares an artificial 

 carbide of iron by coking an intimate mixture of finely divided iron 

 and pitch, or other hydrocarbon ; the result being a heavy metal- 

 liferous coke, which, when ground fine and mixed with caustic 

 soda in the fused condition, blends intimately with it, and causes 

 the reduction of the soda at a temperature very much below that 

 hitherto found possible, namely, below that of melting silver, which 

 has been estimated to be about 1000° C. The chemical re-action 

 during reduction cannot be confidently defined, but it probably is 

 somewhat according to the following formula : — 



4NaHO + FeC2 = Na2C03 +Fe + 2H2 + CO + Na^ ; 

 that is to say, four molecules of caustic soda and one molecule of 

 the carbide of iron, as above defined, produce, in the liquid form, 

 one molecule of carbonate of soda and one atom of iron ; while 

 two molecules of hydrogen, one molecule of carbonic oxide, and 

 one molecule of sodium, escape in the gaseous state. The 

 hydrogen and the carbonic oxide ignite, and burn with a bril- 

 liant flame colored by the characteristic sodium hue, while the so- 

 dium distils, and condenses into suitable vessels. The reduction 

 thus takes place in an abundant atmosphere of hydrogen and car- 

 bonic oxide, which effectually preserves the sodium from oxidation 

 till it can be safely deposited in mineral oil. 



The apparatus for preparing the sodium is sufficiently simple. 

 The caustic soda is received in drums from the neighboring alkali 

 works of Messrs. Chance Brothers. The finely divided iron is 

 mixed with melted pitch in iron pots set in a suitable' stove, and 

 the mixture of pitch and iron is then calcined into coke m large 

 iron retorts set in an ordinary furnace. 



The metalliferous coke is ground into a fine powder by means of 

 ordinary edge-runners, and is ready for charging into the sodium- 

 retorts, which are of specially ingenious construction, and deserve 

 a detailed description. Each furnace is heated by gas, applied on 

 the regenerative principle, and contains five cast-steel crucibles, or 

 pots of an egg-shaped form, arranged with their long axes vertical. 

 The upper part of the egg is formed into the head or cover, much 

 like the artificial Easter eggs which contain sweets ; but it is fitted 

 with a vertical pipe, which passes up through the top of the fur- 

 nace, and forms the passage by which a portion of the charge is 

 introduced, and it also has a lateral branch connected to the con- 

 denser, which consists of a small cast-iron vessel of peculiar form, 

 arranged so as to allow the fluid sodium to trickle out, to let the 

 hydrogen and carbonic-oxide gases escape, and to afford facilities 

 for cleaning the passage, so as to prevent it from becoming choked. 

 The form of this condenser is of some importance, if the best results 

 are to be obtained. The whole of the head above described is se- 

 cured immovably in the upper part of the furnace, and is protected 

 by the oven- setting from extreme heat ; it can, however, be readily 

 removed if desired. The lower part of each retort rests on the top 

 of a vertical hydraulic lift, which is worked by a moderate water- 

 pressure, provided by a special duplex pump ; and it is this press- 

 ure, which, with the interposition of some luting, forms the joint 

 between the head of the retort and its lower portion. The upper 

 part of the lift or platform is so arranged, that, when the retort 

 resting on it is in its place, the aperture in the bottom of the fur- 

 nace is completely closed. When the lift is lowered, the bottom 

 half of the crucible sinks to the floor level ; and a two-wheeled iron 

 hand-truck of special construction is wheeled up, and catching hold 

 of the crucible by two projections on its sides, provided for the 

 purpose, lifts it off the hydraulic ram, and by the aid of two men 

 transports it to the " dumping " pits, on the edge of which it is 



turned on its side ; the liquid carbonate of soda and finely divided 

 iron, which form the residue, are turned out ; and the inside is 

 scraped clean from the opposite side of the pit, under the protec- 

 tion of iron shields. When clean inside and out, the crucible is 

 again lifted by the truck, and carried back to the furnace, receiving 

 a portion of the fresh charge on its way. It is then again placed 

 on its ram and lifted to its place, having still retained a good red 

 heat. It takes two minutes only to remove and clear a crucible ; 

 from six to eight minutes performs the same office for the set of 

 five ; and the whole cycle of operations, including the distilling of 

 the sodium, requires one hour and fifteen minutes. The five cruci- 

 bles yield 500 pounds of sodium per twenty-four hours ; so thai 

 the battery of four furnaces is competent to yield 2,000 pounds, or 

 nearly one ton, of sodium per day. 



The only portions of this plant liable to exceptional wear are the 

 bottom halves of the crucibles, the durability of which is found to 

 depend very much on the soundness of the cast steel of which they 

 are made, because any pores or hollows are rapidly searched out by 

 the furnace flames. The average duration of each crucible at 

 present is about 750 pounds of sodium, or 125 charges. The car- 

 bonate of soda removed from the retorts is returned to the alkali- 

 makers, and is again converted into caustic soda, fit for further 

 use. 



The six pounds of sodium, the produce of each charge, is al- 

 lowed to trickle from the condensers into small iron pots, in which, 

 when cool enough, it is covered with mineral oil, and then trans- 

 ported to the sodium-store, where it is melted in large pots, which 

 are heated by an oil bath, and cast into ingots of convenient form 

 for the subsequent operations. The strong affinity of sodium for 

 oxygen is well known : hence it is best kept covered by an oil, 

 such as mineral oil. which does not contain oxygen in its composi- 

 tion ; and the greatest care has to be taken to protect it from water, 

 because water is decomposed with so much energy by sodium, that 

 the heat caused by the clashing-together of the atoms of sodium 

 and the oxygen of the water is sufficient to ignite the liberated hy- 

 drogen. Hence the apparent paradox, that, to make the sodium- 

 store fireproof, it is necessary to make it waterproof also, and at 

 the same time to avoid naked lights, which may chance to set the 

 vapor from the oil on fire. 



We have now got the two ingredients required for the produc- 

 tion of aluminium ; namely, the double chloride of aluminium and 

 sodium, and metallic sodium. The double chloride is broken into 

 small pieces, and mixed with cryolite (the native fluoride of alu- 

 minium and sodium, 6 Na F APF"), and with metallic sodium cut 

 into thin slices by an ordinary tobacco-cutting machine. The mix- 

 ture is tightly enclosed in a revolving wooden box, in which it gets 

 thoroughly mixed. This part of the process is somewhat trying, 

 on account of the hydrochloric-acid gas given off by the double 

 chloride, which slowly decomposes when exposed to the air. 

 When the ingredients are sufficiently mixed, they are turned out 

 on to the hearth of a regenerative reverberatory furnace, over which 

 the mixing cylinder is placed. The hearth is made to slope to- 

 wards a lateral opening, whichJs closed during the process of re- 

 duction by clay, supported by iron plates and keys. There are two 

 furnaces, — a small one, capable of producing 60 pounds of alu- 

 minium per charge ; and a large one, which yields 140 poundSi 

 The charge introduced into the furnace melts quickly ; and a re- 

 action, represented by the following formula, takes place : — 



2 (Na CI) AljClj -H 3 Na, = 8 Na CI +■ Al^ . 

 That is to say, one molecule of the double chloride and three mole- 

 cules of sodium yield eight molecules of common salt and one 

 molecule of aluminium. The process of reduction lasts about 

 three hours. The melted slag, which consists chiefly of common 

 salt and the cryolite (which merely served as a flux), is drawn off by 

 breaking the clay stopping of the hearth-opening from above down- 

 wards ; and finally the lower tapping-hole is broken through, and a 

 silvery stream of metallic aluminium runs out, and is received into 

 cast-iron moulds. The reducing operation requires considerable 

 skill, and great attention to the temperature of the furnace, which 

 has to be varied during the continuance of the re-action. 



The large furnace is competent to produce 840 pounds of alu- 

 minium per day of twenty-four hours ; and the small one, 360 

 pounds. 



