62 



SCIENTIFIC NEWS. 



[Maj' 2nd, li 



merits. Articles likely to come into immediate contact with 

 the skin were for the most part worn colourless. The only 

 exceptions were flannels dyed with cochineal, which were 

 deemed salutary in rheumatism, and stockings, dyed either 

 black with copperas and logwood in the old-fashioned style, 

 dark blue with indigo, or greys made by " scribbling " the 

 above blacks and blues with undyed wool. 



But now materials dyed all the colours of the rainbow 

 are worn in immediate contact with the skm, and complaints 

 of unpleasant consequences not rarely " go the round of the 

 papers." Now, many of these complaints are grossly ex- 

 aggerated ; some carry impossibility on their very face, but 

 there still remains, we fear, a basis of fact. It may be 

 urged with truth that arsenic is no longer employed by 

 the leading colour manufacturers in the preparation of 

 aniline colours, and that neither their workmen nor those 

 in our great dye-works complain of any unpleasant results. 

 But it seems that a colour which has no action on the hands 

 may cause irritation if kept in close contact with the skin of 

 the feet or the chest, being all the time exposed to the action 

 of perspiration. Hence, the wiser course is to use for 

 under-garments undyed materials only. 



We have not here entered upon the question of " poisons 

 in the workshop," which, for the present, would take us 

 too far. 



THE ELECTRIC FURNACE AND THE 

 PRODUCTION OF ALUMINIUM AND 

 ITS ALLOYS. 



THE metal aluminium has recently attracted considerable 

 attention, and as there appears to be a probability of 

 its use being very greatly extended in the near future, we 

 give a brief account of it, and of two new allied processes 

 for its production, which are believed to contain the pro- 

 mise of great success. 



Aluminium probably exists in the earth's crust in greater 

 quantities than any other metal. It has an enormous dis- 

 tribution in the form of its oxide alumina in combination 

 with silica and other bases. The most familiar of its native 

 compounds is felspar, which is one of the constituents of 

 granite and of several other igneous rocks. The clays are 

 more or less pure combinations of alumina and silica, pro- 

 duced by the disintegration of felspar. When pure the 



Fig. I. 



clay is quite white, as we see in the porcelain clay of 

 Devonshire and Cornwall, which is derived from colourless 

 felspar. 



The uncombined oxide, alumina, is not common. It is 

 found, for instance, as corundum, as the gems amethyst, 

 ruby, and sapphire. Indeed, all the crystalline varieties of 

 alumina are exceedingly hard, the most common being 

 emery, so well known as a polishing substance, and which 

 is mainly corundum coloured with iron oxide. 



In spite of the abundant supply of aluminium compounds, 

 the metal itself is so rare and costly, that it may almost be 

 classed as one of the precious metals. But although in the 



metallic state it has hitherto only been obtained with com- 

 parative difficulty, aluminium has for long attracted the 

 attention of metallurgists on account of its possessing quali- 

 ties which render it remarkably suitable for use in the arts, 

 and for many purposes connected with engineering and 

 warfare. Thus its specific gravity is only 2-67, it being 

 rather lighter than glass, only a quarter as heavy as silver, 

 and one-third the weight of iron. This property was taken 

 advantage of by Napoleon III., who ordered the eagles 

 surmounting the standards of the French army to be made 

 of aluminium instead of silver. Aluminium is not acted 

 on by air even at very high temperatures, and sulphuretted 

 hydrogen, the gas which so readily tarnishes silver, has no 

 effect on it. In fact, it is found to preserve its appearance 

 — that of a bluish-white metal somewhat resembling silver 

 — almost as well as gold does. In the form of certain 

 alloys it has great beauty and strength ; thus the gold-like 



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alloy of which watch-chains, pencil-cases, and other orna- 

 mental articles are constructed, consists of about one part 

 of aluminium and nine parts of copper. It is the enormous 

 strength of some of these alloys or aluminium-bronzes that 

 constitutes their most valuable quality from a practical 

 point of view. This will be understood when we say that 

 the official trials of aluminium-bronze castings have shown 

 a tensile strength which far exceeds that of any forged 

 iron or steel when made into heavy guns; and thus that 

 guns, avoiding all forging, welding, and shrinking on of 

 rings, can be cast in any ordinary foundry and finished in a 

 lathe. Tempering, drilling, and annealing, now required 

 in the construction of heavy ordnance, would also be un- 

 necessary. An extensive use of aluminium must ensue if 

 a cheap process for obtaining it can be developed. Another 

 use of a very promising character has been introduced by 

 Mr. Nordenfeldt, of machine-gun fame, who has found that 

 it is possible to obtain articles of cast-iron equal in strength 

 to wrought-iron, if a little aluminium is mixed with the molten 

 metal. This effect appears to be due to the fact that the 

 small amount of aluminium causes the iron to fuse at a 

 much lower temperature than would otherwise be required. 

 Mr. Nordenfeldt has given the name "mitis metal " to iron 

 heated in this way. 



Aluminium has usually been obtained from one of its 

 native compounds, a mineral known as cryolite, by an 

 extensive and rather complicated smelting process. It 

 now appears probable that we shall have it sup- 

 plied at a comparatively cheap rate by a new process, 

 which has been invented and developed by Messrs. E. H. 

 and A. H. Cowles. This process is extremely interesting, 

 not only on account of its novelty, but because it is ap- 

 plicable to many other than aluminium compounds, and 

 opens out a series of possibilities the importance of which 

 it is difficult to over-estimate. 



The process of the Messrs. Cowles consists, briefly, in the 

 use of an electric furnace, in which the temperature attained 

 is much higher than has been possible hitherto, and by 

 means of which highly refractory substances, such as corun- 

 dum, may be fused and made to undergo decomposition and 

 recombination. The current for heating the furnace is ob- 

 tained from large and powerful dynamo-electric machines. 

 A small experimental Cowles furnace is shown in Figs, i 

 and 2. It consists of an oblong box of fire-brick, the interior 



