METALLURGY. (ALUMINUMZINC.) 



359 



Aluminum. Most of the investigations hav- 

 ing for their object the use of aluminum as a 

 source of heat have been conducted by Dr. Hans 

 Goldschrnidt, of Essen, and it is through his la- 

 bors, according to Sir W. C. Roberts-Austen, that 

 metallurgy is entering upon a new phase. In its 

 simplest form, Dr. Goldschmidt's process consists 

 in igniting a mixture of oxid of iron, ferric oxid, 

 and finely divided aluminum. To this mixture the 

 name of " thermit " is given, and several varieties 

 of it, adapted to various kinds of work, are used 

 by Dr. Goldschrnidt at his furnaces. The mixture 

 is placed inside of a crucible and ignited by a 

 small piece of magnesium wire, which serves as a 

 kind of wick if it is placed in a little heap of cal- 

 cium sulfate and aluminum. The aluminum ex- 

 tracts oxygen from the oxid of iron (for in- 

 stance), and a sufficiently intense heat is pro- 

 duced, not only to melt the iron which is liberated 

 from its oxygen, but also to melt up the slag, and, 

 further, to leave a considerable surplus ot heat, 

 which is available for doing other work. No 

 known pyrometer will enable the heat to be 

 measured. The author believes it is about 5,000 

 C. The ignited and molten mass in the crucible 

 is so intensely hot that it may be made to unite 

 surfaces of steel that require to be joined, such 

 as the ends of the lengths of rails, it being ap- 

 plied, as the author compares it, as a hot bandage 

 might be applied to a wound in surgical treat- 

 ment. Its work is well comparable with that of 

 the electric arc. The very hot molten iron may 

 also be used for repairing defective castings. By 

 mixing other metallic oxids with the iron oxid, 

 the metals they contain are reduced and alloy 

 themselves w 7 ith the iron, and the composition of 

 the defective casting can thus be matched. It is 

 likewise possible to produce directly steel of a 

 suitable degree of carburization. The use of 

 aluminum as a reducing agent has been dwelt 

 upon in other years. Manganese and chromium 

 containing only small quantities of carbon are 

 now produced on a large scale for industrial use 

 metals which are important, chromium in the 

 metallurgy of steel and manganese in that of cop- 

 per. Alloys of manganese and zinc are likely to 

 prove of value. Other alloys that have been thus 

 obtained are those of manganese and chromium ; 

 ferro-titanium ; of titanium and manganese; of 

 iron and boron; ferro-vanadium ; and of lead and 

 barium. The solid product of the combustion of 

 aluminum is alumina of a high degree of purity, 

 in the specially interesting form of ruby-tinted 

 crystalline masses resembling the natural ruby. 



In using aluminum as a fuel or as a reducing 

 agent the question arises as to what extent it 

 must be heated before it will begin to extract 

 oxygen from the air or an oxid. The presence 

 of a little mercury, Sir W. C. Roberts- Austen says, 

 enables aluminum to oxidize more readily, and it 

 will burn sooner in oxygen if its combustion is 

 started by a fragment of charcoal. The tempera- 

 ture at which it will abstract oxygen from a me- 

 tallic oxid will depend upon the oxid submitted 

 to the action. 



A new method of precipitating pure alumina 

 described by C. M. Hall consists in charging 

 bauxite (calcined at a red-heat if necessary), 

 burned lime, sodium carbonate, and water into a 

 digester provided with a stirrer and subjecting 

 the mixture at a considerable pressure to an 

 elevated temperature for from one to three hours. 

 Insoluble carbonates and silicates and inert im- 

 purities of the bauxite, such as iron oxid insolu- 

 ble alumina, etc., will form a residue to be sepa- 

 rated by nitration from the insoluble sodium alu- 

 minate. From the latter aluminum hydroxid is 



arid and 

 um r-ar- 



precipitated in the usual way by c-.nl, 

 filtered off. The filtrate, with it 

 bonate, is concentrated by heating ,n 

 with another charge. 



In experiments by L. Tetmajor, the !,<.- t ; - ft 

 alloy of aluminum brass was obtained , t], :;j 

 per cent, of aluminum, while hard allo\ 

 made with 1.4 per cent. The breaking sti 

 rapidly with increasing percentages of alu 

 Silicon acted in the same manner. 1 he 

 ments with aluminum bronze showed that up 

 to from 5 to 10 per cent, of aluminum the strength 

 increased, while the breaking strain fell. The pres- 

 ence of iron and silicon gave similar results. It 

 was further shoAvn that a 10-per-cent. aluminum 

 bronze containing 1.5 per cent, of iron and silicon 

 was too brittle for ordinary use. Pure aluminum 

 was malleable when cold, as was also the bronze. 

 When, ho\vever, the quantity of aluminum in the 

 latter amounted to 10 per cent., the malleability 

 had practically vanished. When hot, the bronze 

 was plastic, malleable, and easily rolled. Hard 

 aluminum bronze Avears Avell in use. The best-, 

 rolled bronze contains from 8 to 10 per cent, of 

 aluminum and silicon together. 



With a neAv modification of the Goldschmidt 

 process for alumino-thermic Avelding and casting 

 (see Annual Cyclopaedia for 1900, p. 3(51), by L. 

 Cohn, an ordinary Avorkman can effect a good 

 weld. The "thermit" mixture (of which 1 kilo- 

 gram yields 150 grams of molten iron) is placed 

 in a crucible made of iron plate lined with re- 

 fractory material, mounted on a substantial 

 tripod and closed at the bottom with one or 

 more small iron plates, according to the quantity 

 of thermit used. The thermit is covered Avith a 

 layer of kindling or priming mixture and an iron 

 plate with a central hole, through which the 

 charge can be ignited by means of a fusee, is 

 placed over the whole. The crucible thus prepared 

 is placed Avith its tap-hole immediately above the 

 gate of a refractory mold built around the ends 

 of the two rails to be joined, Avhich are so clamped 

 together that the surfaces to be welded are pressed 

 against each other. In a few seconds after the 

 charge is ignited the contents of the crucible 

 should become fluid, and melting away the sup- 

 porting plate, should flow into the mold and 

 make the required joint. In this process it is the 

 molten iron that first enters the mold, and the 

 molten corundum slag floating on the top passes 

 out last instead of first, as in the older teeming 

 process. The method lends itself well to the 

 jointing of rails already laid, and insures a sound 

 electrical contact; it is of no use, however, for 

 rails of which the ends are worn. The process can 

 not Avell be applied to the welding of tubes, as the 

 hot metal is liable to melt its Avay through the 

 tube at first contact. It is, hoAvever, very suitable 

 for the repair of broken shafts or rails, and is 

 especially recommended for use on board ship, as 

 the appliances required are exceedingly simple 

 and convenient. 



Zinc. Among metallurgical problems men- 

 tioned by J. W. S\van in his presidential address 

 before the Society of Chemical Industry as still 

 awaiting satisfactory solution, one of the fore- 

 most in importance is the economical extraction 

 of zinc from its ores. The present methods in use 

 are very Avasteful, and a practicable "electrolytic 

 method is much to be desired. The difficulties 

 in the way of a successful electrolysis have not 

 yet been fully overcome. Experimental operations 

 at Hayle, in Cornwall, by the process of Cowper- 

 Coles gave indifferent results. At Milton, in Staf- 

 fordshire, fairly satisfactory success was obtained 

 Avith the SAvinburne-Ashcroft fusion process; and 



