Aluminium and its future in the arts.

Practical Magazine 18, 1876

It is now about twenty years since the celebrated French Chemist, Deville, succeeded in demonstrating the possibility of producing the metal aluminium upon a large scale; but up to the present, the extent to which this interesting and praiseworthy invention has been utilized has but to a slight degree realized the sanguine expectations which intelligent minds of all professions have been accustomed to associate with it. So important, indeed, were the fruits of Deville's first investigations deemed to be, that they were at once invested with the dignity of royal patronage, and the first works for the manufacture of the new metal were shortly there after erected at Javelle, near Paris, from the private purse of the late Emperor of the French. It was expected that the new product would at once find its way into the useful arts as an effective and valuable substitute for many other metals. That these expectations were well founded, will be apparent from the characteristic and very exceptional properties of the metal. A bright, pure surface of aluminium possesses a greyish white colour, something between that of zinc and tin. Its extreme lightness is one of its very distinguishing properties, and affords an immediate means of identifying it from every other metal– its specific gravity is but 2.5 (water = 1), from which it appears that it is about three times lighter than copper, four times lighter than silver, and nearly eight times lighter than gold. When struck it emits a loud, clear, musical tone, which has been compared with that of crystal glass. The keen observing powers of the French chemist did not permit this property to pass unnoticed. He suggested the employment of aluminium for bell-metal, and in the year 1868 presented to the Royal Institution of Great Britain a bell a foot and a-half in diameter, which proved to possess a most exquisite tone, and which, despite its not inconsiderable dimensions, weighed no more than forty-four pounds.

The metal may be hammered out into the thinnest leaves, rolled into plates or sheets, and drawn into the finest wire. Its hardness approaches that of fine silver, and its tensile strength equals that of copper. Its melting point lies at 700° C. (about 1,300 Fahr.), or between that of zinc and silver; and it is worthy of note that it fuses with extreme slowness, and does not vaporize even in the heat of the blast furnace. Generally speaking, the metal is workable to an extraordinary degree, and it may be filed, turned, pressed, engraved, and coined quite readily. In compact masses the metal is quite indifferent to atmospheric influences, and even when being smelted, it does not sensibly oxodize. It must be remarked, however, that the properties above enumerated are predicated from the presumption that the metal is free from impurities.

The adaptability of aluminium as a circulating medium to substitute the great variety of small coin of various compositions now employed in the different countries, was strongly urged at the outset by Deville; and as long ago as 1855, a large and beautifully executed medallion of this metal, made under his direction, and presented to Prof. Wöhler, its first discoverer, attracted much attention. The properties of aluminium, which have been appealed to as establishing its admirable fitness for coinage into money, are, in addition to its colour, klang, and ease of manipulation, its extreme lightness, which would serve as a perfect check upon its fraudulent imitation, and especially its indifference to atmospheric influences. In this latter respect it is far superior to silver and copper, and the alloys of these metals, at present so largely employed for this purpose. Weights of aluminium, for example, have for a number of years been employed, and have proved to be excellently adapted for the most delicate work of precision in the laboratory, retaining their accuracy even after years of use. The same admirable conser vation has been remarked upon the numerous articles of luxury and fancy, which, immediately after the first public knowledge of the metal, it became the fashion to possess. Nor can it be urged with much reason that it is undesirable for coinage purposes because of the possibility of the discovery in the near future of some simple method of producing the metal from clay — which is known to contain it in considerable proportion — since this problem has been repeatedly attacked and as often abandoned as hopeless of solution; and the price of the metal has remained very constant for a number of years.

It may be considered an objection to its employment for monetary purposes, that it is energetically dissolved by a solution of soda or potash; but in reply, it may be remarked that silver and copper are equally objectionable in this particular, since they are both eagerly dissolved by nitric acid, to the action of which aluminium is quite indifferent. Upon the whole, it appears to the writer that the permanency of the metal, by which is meant its great stability when exposed to atmospheric influences and its indifference to the action of many of the usual solvent agents, and the great difficulty attending its production in large quantities, fairly entitle aluminium to be ranked with the noble metals; and when, in addition to the foregoing, its very exceptional properties are called to mind, the metal may justly claim careful consideration on the part of those who interest themselves with the question of reforming the world's circulating medium.

In the manufacture of jewellery and other articles of luxury, it is probable that aluminium may in time play an important part, though it is scarcely possible for it to ever rival the popularity of silver in these uses. In Paris, which by the way has always remained the head-quarters of the aluminium industry, it appears to be employed to a considerable extent for elegant inlaid work upon jewel and dressing-cases, fans, &c., for lids and covers of glasses, and for a variety of small articles of galanterie. From what has been done in this direction, we can estimate its fitness for a thousand elegant articles of taste, fancy, and utility, when once its popularity is established before the world at large, which is now scarcely cognizant of the existence of such a metal as aluminium. The clock and watch-makers' arts, the manufacturers of surgical and musical instruments, and of artificial teeth, and especially the manufacturers of fancy articles, such as seals, pen-holders, paper-weights, smokers’ and sportsmen's necessaries, shirt and sleeve buttons, canes and riding-whips, harness decorations, statuettes, gas-fixtures and lamps, and of other articles too numerous to mention, would without doubt derive much advantage and profit from the employment of aluminium, and sooner or later its peculiar fitness for these uses will be recognized.

For the manufacture of philosophical and engineering instru ments, and especially the latter, the indifference of aluminium to atmospheric influences and its extreme lightness, have of late met with general recognition, and the employment of the metal for these uses is steadily growing in favour.

For household utensils, likewise, aluminium has been highly recommended; but though, for this purpose as for others, neither a want of desirable properties nor excessive costliness have stood in the way of its introduction, it has been opposed by the despotic rule of custom or fashion, and in no instance with less show of reason. How much, for example, has been written and spoken concerning the danger of poisoning from the vessels employed in preparing food P How many warnings have been uttered against using copper cooking utensils, pots with lead glazing, and silver spoons that form verdigris? Were these household goods made of aluminium, we should be in possession of vessels that, so far as outward appearance and durability go, leave very little to be desired; that, furthermore, would be far more convenient to handle than the customary wares they would replace; and, what is of perhaps more importance, that would be perfectly innocuous. It appears somewhat curious that the experiment has never been tried of introducing the use of aluminium spoons. The present or prospective cost of aluminium can scarcely be offered as an objection thereto, for this is now only about one-half that of silver; while the difference in the specific gravity of the two metals is so considerable, that for the money value of one silver spoon of good quality, one might obtain no less than seven spoons of aluminium, of equal size and strength.

That prejudice and fashion are to some extent to blame for the general want of appreciation, and even total ignorance, of the eminently fitting characteristics of the new metal for a variety of uses, is very manifest; and the clearing away of such obstacles is generally a matter of great difficulty.

The alloys of aluminium are, however, worthy of special consideration, and there is a reasonable probability that a wide field of utility may be open for them in the future. Dr. Biedermann, referring to this subject, remarks, "although there is no mistaking the fact that the high expectations with which the appearance of aluminium filled the public mind have not been fulfilled, yet the aluminium industry has a safe guarantee of its existence in the use of the metal for aluminium alloys, which are capable of the most extensive use on account of their excellent qualities." The only aluminium alloys which have, however, acquired importance in the arts, are the so-called aluminium bronzes.

According to M. Morin, the director of the manufactory of Nanterre, very homogeneous alloys are obtained with copper and 5, 7½ and 10 per cent. of aluminium. The alloys with 5 and 10 per cent of aluminium are both of a golden colour, whilst that with 7½ per cent. has a greenish tint. Even so small an addition as I per cent. of aluminium to copper, according to another authority, considerably increases its ductility and fusibility, and imparts to it the property of completely filling the mould, making a dense casting free from air-bubbles. At the same time the copper becomes more resistant of chemical reagents, increases in hardness without losing in malleability, and unites in itself the most valuable qualities of bronze and brass. A copper alloy with 2 per cent. of aluminium is said to be used in the studio of Christofle, in Paris, for works of art. It works well under the chisel and graver.

The true aluminium bronzes, according to Rudolph Wagner, were first made by John Percy, in 1856. As above referred to, they are alloys containing 90 to 95 per cent. of copper with 10 to 5 per cent. of aluminium. The direct mixture, by first fusion, of 10 parts of aluminium and 90 of copper, gives a brittle alloy, which, however, increases in strength and tenacity by several successive fusions. At each operation a little aluminium is lost. After the compound has been melted three or four times, however, the proportion of aluminium does not appear to change, and the alloy may be again remelted several times without alteration. These fusions are effected in crucibles. The aluminium bronze is homogeneous, and possesses sufficient expan sion to fill the remotest parts of the mould. It affords sharp castings that can be worked more readily than steel. Aluminium bronze may be forged at a dull red-heat, and hammered until cooled off without presenting any flaws or cracks. Like copper, it is rendered milder and more ductile by being plunged into cold water when hot. The bronze polishes beautifully, and pos sesses great strength — according to Anderson's experiments, an average of 75,618½ lbs. per square inch. The resistance to compression is feeble. From the experiments of Col. Strange, on the relative rigidity of brass, ordinary and aluminium bronze, it appears that the last named is 40 times as rigid as brass, and 3 times as rigid as ordinary bronze.

Other experiments have shown that aluminium bronze does not expand or contract as much as ordinary bronze, or brass; that under the tool it produces long and resisting chips, does not clog the file, engraves nicely, etc.; that it is easily rolled into sheets; that in the melted state it expands very much, and is fit for the sharpest castings; but that, as it cools off rapidly, it is subject to shrinkage, and hence to cracks when the articles are bulky, hence requiring numerous runners and a heavy feeding head; and lastly, that, although not entirely unoxidizable, it is not so readily tarnished by contact with the air as polished brass, iron, steel, etc. Dr. Biedermann speaks very highly of this metal. "In the construction of physical, geodic, and astronomical instruments," he says, "it is far preferable to all other metals. In jewellery and articles of art and luxury it is employed in large quantities. Many kinds of house utensils are made of it, and it is also adapted to journal and axle boxes. Gun and pistol barrels, as well as rifled cannon, have been made of it, and have done excellent service." It has been highly recommended for type metal; type made of it last ing, it is affirmed, fully 50 times as long as those from common type metal; it has been employed for the bed of perforating machines for perforating postage stamps; and for the main-springs of watches (90 copper and 5 aluminium), being very hard and elastic, not magnetic, and less liable to rust than steel. Its price, however, ranging as it does from $3 to $10 per lb., according to its percentage of aluminium, is probably the greatest impediment to its common use.

Aluminium alloys with many other metals have been made — notably with silver and iron — but none of them have acquired a permanent value in the arts. They may be passed over with the brief remark that aluminium containing 4 per cent. of silver is employed for the beams of fine balances — for which it is peculiarly fitted from its comparative lightness and stability; and that the addition of a small percentage of aluminium to steel is claimed to impart special virtues to the latter — a claim which, however, has not yet been well established.

In another direction, namely, in electro-plating and coating other metals with aluminium, numerous experiments have been tried, but thus far without practical result.

A few words more concerning the process of manufacture and the present commercial importance of the metal, and we have done. Its metallurgical production is as follows:

Aluminium is manufactured by decomposing the double chloride of aluminium and sodium, with the aid of metallic sodium. The sodium (which, by the way, has been materially cheapened in price since the establishment of the aluminium industry) is obtained by heating to redness a mixture of one hundred parts of calcined soda, fifteen parts of chalk, and forty-five parts of coal. The chloride of aluminium is prepared by passing chlorine gas over a moderately heated mixture of pure alumina (obtained either from alum, or the mineral bauxite), common salt and coal-tar. This operation is conducted in an iron gas-retort, and the result of the interaction of the several substances present is the combination of the coal-tar with the oxygen of the alumina, and the production of aluminium chloride, which unites with the chloride of sodium (common salt), forming a double salt, which volatilizes and is passed off into a separate chamber, where it condenses. From this method of obtaining the chloride, it is impossible to keep it free from chloride of iron, for which reason it is invariably present in the Parisian aluminium. From this double chloride of aluminium and sodium, the metallic aluminium is obtained, either by passing it in the form of vapour over a heated surface of metallic sodium, in a simply constructed and connected system of iron cylinders appropriately heated; or the materials are at once mixed and heated.

Rose, of Berlin, instead of the artificially prepared aluminium chloride, employed the mineral kryolite (a natural compound oc curring in deposits of considerable magnitude in Greenland, and consisting of fluoride of aluminium and sodium) quite successfully. By heating this mineral with sodium, metallic aluminium and fluoride of sodium are produced, and the latter compound is gotten rid of by treating the resulting mass with caustic lime. Of late the metal has also been manufactured from the mineral bauxite.

At present there are four aluminium works in existence, of which three are in France and one in England. Their total production amounts to about 3,500 lbs. yearly, of which 2,000 lbs. are produced in France, 1,500 lbs. in England. Its market value has averaged about $15 per lb., and has been for some years stationary at that figure.

Polytechnic Review.

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