PART XII.

ALLOYS OF ALUMINIUM.

General Remark.-Mierzinski:

"Aluminium unites easily with most metals, the combination being usually accompanied by a lively disengagement of heat. Quite homogeneous alloys can be made, which for the most part are easily worked and have important applications. The alloys in general become harder the greater the proportion of aluminium, and become brittle if this proportion passes a certain limit, which with gold and copper is very low. On addition of a larger amount of aluminium than this limit allows, gold and copper become whiter, and at last entirely lose their color. The addition of other metals to aluminium imparts to it the same new properties. It becomes brighter and somewhat harder, but, united with small quantities of zinc, tin, gold, or silver, remains malleable. Iron and copper impart to it no specially prejudicial qualities, if they are not present in too large quantities. The alloys most frequently used are those of copper, silver, and tin. These owe their numerous uses to their fine color, their resistance to most chemical agents, and the facility with which they may be worked."

ALUMINIUM AND SILICON.

Tissier: "As Deville has observed, silicon is far from injurious to the malleability of aluminium, the latter bearing it much as iron and copper do. We have had occasion to analyze a specimen of aluminium, which, although it worked with difficulty, was yet employed to make various objects, and yet, attacked by HCl, it left an insoluble residue of no less than 15.67 per cent. But, even admitting that this residue still retained some aluminium with the silicon, we think that there was at least 10 per cent. of the latter in this specimen.'

Deville: "Any siliceous material whatever, put in contact with aluminium at a high temperature, is always decomposed; and if the metal is in excess there is formed an alloy or a combination of silicon and aluminium in which the two bodies may be united in almost any proportions. Glass, clay, and the earth of crucibles act in this way. However, aluminium may be melted in glassware or earthen crucibles without the least contamination of the metal if there is no contact between the metal and the material; the aluminium will not wet the crucible if put into it alone. But, the moment that any flux whatever facilitates immediate contact, even sodium chloride does this, the reaction begins. to take place, and the metal obtained is always more or less siliceous. It is for this reason that I have prescribed in melting aluminium not to add

any kind of flux, even when the flux would not be attacked by the metal. Among the fusible materials which facilitate the melting of aluminium, it is necessary to remark of the fluorides that they attack the siliceous materials of the crucible, dissolving them with great energy, and then the siliceous materials thus brought into solution are decomposed by the aluminium with quite remarkable facility. Aluminium charged with silicon presents quite different qualities according to the proportion of the alloy. When the aluminium is in large excess, there is obtained what I have called the 'cast-iron' state of aluminium, by means of which I discovered crystallized silicon in 1854. This 'cast' aluminium, gray and brittle, contains according to my analysis 10.3 per cent. of silicon and traces of iron. When siliceous aluminium is attacked by hydrochloric acid, the hydrogen which it disengages has an infected odor, which I formerly attributed to the presence of a hydrocarbon, but which we now know is due to hydrogen silicide, SiH“, thanks to the fine experiments of MM. Wöhler and Buff. It is by the production of this gas that may be explained the iron smell which is given out by aluminium more or less contaminated with silicon. But aluminium may absorb much larger proportions of silicon, for, on treating fluo-silicate of potash with aluminium, M. Wöhler obtained a material still metallic containing about 70 per cent. of silicon, sometimes occurring as easily separable

crystals. Since I had the occasion in a work which I published on silicon to examine a large number of these combinations, I found that they were much more alterable than pure aluminium or silicon, without doubt because of the affinity which exists between silica and alumina. I have, therefore, dwelt on and tried to explain the importance of this point in obtaining perfectly pure aluminium. I should say, in addition, that the metal now sold in commerce may contain either iron or silicon, according to the method of preparation. These two impurities are hurtful to most of the qualities of the aluminium, and everything ought to be done to avoid their presence."

ALUMINIUM AND MERCURY.

Deville: "Mercury is not able to unite with aluminium. Experiments of this nature which I have made myself, and which Mr. Wollaston has confirmed, prove it most clearly."

Watts: "According to Caillet, aluminium may be amalgamated by the action of ammonium or sodium amalgam, with water; also when it is connected with the negative pole of a voltaic battery and dipped into the mercury moistened with acidulated water, or into a solution of mercuric nitrate. Tissier confirms this statement respecting the

* Compt. Rend., xlix. 56.

battery method, and adds that if the aluminium foil is not very thick it becomes amalgamated throughout and very brittle." Tissier also finds that aluminium may be made to unite with mercury merely by the intervention of a solution of caustic potash or soda, without the intervention of the battery. If the surface of the metal be well cleaned, or moistened with the alkaline solution, it is immediately melted by the mercury, and a shining amalgam forms on its surface. The amalgam of aluminium instantly loses its lustre when exposed to the air, becoming heated and rapidly converted into alumina and mercury. It decomposes water with evolution of hydrogen and formation of alumina and mercury. Nitric acid attacks it with violence.

Watts (First Supplement) states that aluminium amalgam may be formed either by bringing the aluminium in contact with mercury containing a small quantity of sodium, or by Joules's method of electrolyzing the solution of an aluminium salt, with mercury for the negative pole ;* but the best method is to heat the two metals together in a gas which does not act on either of them. To do this, a piece of aluminium foil is placed at the bottom of a thick-walled test-tube, and well-dried mercury is poured on it, the tube having been previously drawn out at the middle to prevent the foil rising

*Chem. Gazette, 1850, p. 339.