April 5, 1889.] 



SCIENCE. 



26s: 



The first portion of metal which runs out, and which forms 

 rather more than three-fourths of the charge, is of the greatest pu- 

 rity ; the remainder, which has to be scraped off the hearth, or 

 which gets entangled in the slag, and has to be subsequently sep- 

 arated out, contains a larger proportion of foreign substances. 

 The cause of the difficulty in obtaining the separation of the metal 

 from its slag consists in the very low specific gravity of aluminium. 



The metal is now taken to the casting-house, arranged like an 

 ordinary brass foundery, is remelted in plumbago crucibles, and 

 cast into ingots, plates, or bars for subsequent sale or manufacture. 



It is evidently impossible to here enter into all the details of 

 manufacture, although these details are of the highest importance 

 in obtaining commercially valuable results. Day by day, as the 

 manufacture progresses, improvements are made which either en- 

 hance the economy of production or increase the purity of the so- 

 dium or aluminium produced. Such improvements in details can- 

 not very well be made public till their value is thoroughly ascer- 

 tained, and the protection of the patent law obtained when consid- 

 ered necessary. 



The following table gives the quantities of the several ingredi- 

 ents employed to make one ton of aluminium : — 



Metallic sodium 6,-ioo lbs. 



Double chloride 22,400 " 



Cryolite 8,000 " 



Coal 8 tons. 



To produce 6,300 pounds of sodium are required — 



Caustic soda 44,000 lbs. 



Carbide made from pitch (12,000 lbs.) and iron turnings (1,000 



lbs.) 7,000 ■' 



Crucible castings 2^ tons. 



Coal 75 " 



For the production of 22,400 pounds double chloride are re 

 quired — 



Common salt 8,000 lbs, 



Alumina hydrate 11,000 ** 



Chlorine gas 15,000 " 



Coal 180 tons. 



For the production of 15,000 pounds of chlorine gas are re- 

 quired — 



Hydrochloric acid 180,000 lbs. 



Limestone dust 15,000 '* 



Lime 30,000 *' 



Loss of manganese 1,000 " 



The works are constructed so as to produce i^ tons of aluminium 

 per week : the quantities of the ingredients consumed are conse- 

 quently half as much again as the figures given in the table. It is 

 easy to see, therefore, that the factory must be on a very large 

 scale ; and the brief account of the process here given indicates 

 also how complicated the manufacture is, and how much care and 

 skill are necessary to conduct it successfully, if pure aluminium is 

 to be made. The great enemies of the metal are iron and silicon, 

 especially the former. When once it gets in, it is impossible to get 

 it out again by any commercially practicable means : hence every 

 precaution has to be taken to insure the purity of the materials ; 

 to which end a well-appointed laboratory, presided over by Mr. 

 Baker, a very able chemist, is kept in active operation. 



Aluminium is endowed with several remarkable properties. It 

 is the lightest of the metals which possess considerable tenacity 

 and hardness. A given volume of aluminium is only a little more 

 than 2i times (2.65) the weight of an equal bulk of water ; whereas 

 iron is yf times, copper nearly 9 times, gold 19* times, and plati- 

 num 21^ times, as heavy as water. The metal has a bright silvery 

 lustre. It is capable of taking a very high polish, and of retaining 

 its brilliancy and color under conditions which would rapidly tar- 

 nish silver, because it does not oxidize from exposure to either dry 

 or damp air, and is unaffected by that great enemy of silver, sul- 

 phuretted hydrogen, or other sulphur compounds present in Lon- 

 don fogs, either at ordinary temperatures or even at a red heat. 

 At ordinary temperatures it is not affected by either strong or di- 

 luted nitric acid. Weak sulphuric acid has no action on it, neither 

 have sulphuretted hydrogen or sulphide of ammonium, which ex- 

 plains the reason why it does not tarnish, even in very impure at- 

 mospheres. Water has no effect on pure aluminium under ordinary 



conditions ; but, if it be made the oxygen pole of a galvanic battery,, 

 it is readily converted into alumina, forming a copious white pre- 

 cipitate. The vegetable acids, such as acetic and tartaric, have no. 

 effect : hence aluminium is admirably fitted for making into cook- 

 ing utensils, coffee-pots, teapots, etc., its extreme lightness being 

 also an advantage for this purpose. It is not acted upon by the 

 hydrates of potassium and sodium in a state of fusion ; but solu- 

 tions of these alkalies in water dissolve it readily, forming alumi- 

 nates of potassium and sodium, with evolution of hydrogen. Of" 

 this property the silversmith takes advantage in producing very 

 beautiful frosted effects, by plunging the polished metal for an in- 

 stant into a weak solution of caustic soda, washing in a large quan- 

 tity of water, and then digesting in strong nitric acid. Its powers, 

 of conducting heat are high in the scale, being about two-thirds, 

 that of copper; its specific heat is .22, only lithium, sodium, and 

 magnesium being above it. Its electrical conductivity is eight 

 times higher than that of iron, and about equal to that of silver.. 

 Its elasticity and tenacity are equal to that of silver, and have been 

 determined by Mr. W. H. Barlow at about 12 tons per square inch ;. 

 but weight for weight, its tenacity would be the same as high-class 

 steel, or 36 tons per square inch, that is to say, bars of equal weight 

 would carry the same loads. Experiments on very fine wire have 

 given the same results. It is very malleable and ductile, when 

 proper attention is paid to annealing during the process of work- 

 ing, — ■ a precaution common to the manipulation of most metals. 

 Aluminium of about 97 per cent to 98 per cent purity may be rolled 

 into thin sheets, and may be beaten into foil as thin as any that 

 can be produced from silver and gold. It can be drawn into very 

 fine wire, of only one-tenth of a millimetre diameter, and ought to 

 supersede silver in the manufacture of metallic braid and tissues, 

 because it will never tarnish as silver does. It can be stamped or 

 spun into hollow ware, but there is as yet some difficulty in solder-, 

 ing it ; at any rate, the process of performing the operation is known 

 to very few people. 



Aluminium forms alloys with most metals. Iron is always more 

 or less associated with it ; but it seems doubtful whether it be a 

 true alloy, or wholly or in part a mixture, like the carbon contained 

 in cast iron and in steel. Silicon is also invariably found asso-- 

 ciated more or less with the metal. Aluminium added to molten 

 iron and steel lowers their melting-points, and consequently in- 

 creases the fluidity of the metal, and causes it to run easily into 

 moulds and set there, without intrapping air and other gases, and 

 forming blow-holes and similar imperfections. It is in consequence 

 used to the extent of about | per cent and less by some steel 

 founders, and seems to render the production of sound steel cast- 

 ings more certain and easy. Admiral Kolokolzoff, the director of 

 the great gun-factory near St. Petersburg, uses ferro-aluminium, — • 

 an alloy with iron, containing 10 per cent of aluminium, — and 

 adds it to the crucibles of melted steel about ten minutes before pour- 

 ing, in the proportion of one pound of the alloy to 80 pounds of 

 steel, which gives one part in 800 of pure aluminium ; and the re- 

 sult is that he. gets the largest steel castings, completely free from, 

 air-bubbles, and with very excellent mechanical properties. 



One of the most remarkable applications of the property which 

 aluminium possesses of lowering the melting-point of metals has 

 been made by Mr. Nordenfelt, in the production of castings of pure 

 iron ; that is to say, iron free from any sensible quantity of carbon or 

 manganese. Pure iron melts at about the same temperature as 

 platinum, that is, about 1700" C. ; yet even then the molten mass, 

 is not liquid enough to be run into moulds, but the addition of from, 

 SDOT t° TTii P^'"' t)y vveight, of aluminium, lowers the melting-point 

 to such an extent that it becomes fluid enough to run into the 

 most minute and intricate forms. Mr. Nordenfelt has given the 

 name of " mitis " (flexible ductile) to his metal. Mr. Anderson 

 then called attention to a wire brush of solid casting, the back and 

 iron bristles forming one mass, and yet the bristles may be bent 

 about just like the softest iron wire. 



The process of manufacture is as follows : Wrought iron is 

 placed in crucibles, which are put into a liquid-fuel air-furnace of 

 peculiar and ingenious construction. In a furnace for six crucibles, 

 for example, they are arranged on an elongated hearth in pairs, 

 cross partition walls being so built as to cause the flame to em- 

 brace each crucible thoroughly. In the roof of the furnace are- 



