and then heat stronger, at last to redness. Cool, and when fully cold put it into a glass of cold water. A gray powder separates out which on nearer observation, especially in sunlight, is seen to consist of little flakes of metal. After it has separated, pour off the solution, filter, wash with cold water, and dry; this is the aluminium."

In reality this powder possessed no metallic properties, and, moreover, it contained potassium and Al2C16, which gave to it the property of decomposing water at 100°. To avoid the loss of AlCl by volatilization at the high heat developed during the reaction, Liebig afterwards made the vapor of AlCl pass slowly over some potassium placed in a long glass tube. This device of Liebig is nearly the arrangement which Wöhler adopted later, in 1845, and which gave him much better results. The following is Wöhler's second paper, published in 1845 :—*

"On account of the violent incandescence with which the reduction of AlCl by potassium is accompanied, this operation requires great precautions, and can be carried out only on a small scale. I took for the operation a platinum tube, in which I placed Al2C1 and near it some potassium in a platinum boat. I heated the tube gently at first, then to redness. But the reduction may also be done by putting potassium in a small crucible

* Liebig's Annalen, 53, 422.

which is placed inside a larger one, and the space between the two filled with A12C16. A close cover is put over the whole and it is heated. Equal volumes of potassium and AlCl are the best proportions to employ. After cooling, the tube or crucible is put in a vessel of water. The metal is obtained as a gray, metallic powder, but on closer observation one can see even with the naked eye small tin-white globules some as large as pins' heads. Under a microscope magnifying two hundred diameters the whole powder resolves itself into small globules, several of which may sometimes be seen sticking together, showing that the metal was melted at the moment of reduction. A beaten-out globule may be again melted to a sphere in a bead of borax or salt of phosphorus, but rapidly oxidizes during the operation, and if the heat is continued, disappears entirely, seeming either to reduce boron in the borax bead or phosphorus or P2O5 in the salt of phosphorus bead. I did not succeed in melting together the pulverulent aluminium in a crucible with borax, at a temperature which would have melted cast iron, for the metal disappeared entirely and the borax became a black slag. It seems probable that aluminium, being lighter than molten borax, swims on it and burns. The white metallic globules had the color and lustre of tin. It is perfectly malleable and can be hammered out to the thinnest leaves. Its specific gravity, determined with two globules weighing 32 milligrammes, was

2.50, and with three hammered-out globules weighing 34 milligrammes, 2.67. On account of their lightness these figures can only be approximate. It is not magnetic, remains white in the air, decomposes water at 100°, not at usual temperatures, and dissolves completely in caustic potash (KOH When heated in oxygen almost to melting, it is only superficially oxidized, but it burns like zinc in a blast-lamp flame."

These results of Wöhler's, especially the determination of sp. gr., were singularly accurate when we consider that he established them working with microscopic bits of the metal. It was just such work that established Wöhler's fame as an investigator. However, we notice that his metal differed from aluminium as we know it in several important respects, in speaking of which Deville says: "All this time the metal obtained by Wöhler was far from being pure; it was very difficultly fusible, owing without doubt to the fact that it contained platinum taken from the vessel in which it had been prepared. It is well known that these two metals combine very easily at a gentle heat. Moreover, it decomposed water at 100°, which must be attributed either to the presence of some potassium or to Al2C1o, with which the metal might have been impregnated; for aluminium in presence of Al2C1o in effect decomposes water with evolution of hydrogen.

After Wöhler's paper in 1845, the next improve

ment is that introduced by Deville, in 1854–55, and this is really the date at which aluminium, the metal, became known and its true properties established. He first read to the Academy an account of his laboratory process, by which he obtained a pencil of the metal. The following is his account:*

"The following is the best method for obtaining aluminium chemically pure in the laboratory. Take a large glass tube about four centimetres in diameter, and put into it pure A12C16 free from iron, and isolate it between two stoppers of amianthus (fine, silky asbestos). Hydrogen, well dried and free from air, is brought in at one end of the tube. The Al2C16 is heated in this current of gas by some lumps of charcoal, in order to drive off hydrochloric acid or sulphides of chlorine or of silicon, with which it is always impregnated. Then there are introduced into the tube porcelain boats, as large as possible, each containing several grammes of sodium, which was previously rubbed quite dry between leaves of filter paper. The tube being full of hydrogen the sodium is melted, the Al2C16 is heated and distils, and decomposes in contact with the sodium with incandescence, the intensity of which can be moderated at pleasure. The operation is ended when all the sodium has disappeared, and when the sodium chloride formed has absorbed so much Al2Cl as to be saturated with it. The Al

*Ann, de. Phys. et de Chem., xliii. 24.

which has been formed is held in the double chloride of sodium and aluminium, Al2C16.2NaCl, a compound very fusible and very volatile. The boats are then taken from the glass tube, and their entire contents put in boats made of retort carbon, which have been previously heated in dry chlorine in order to remove all silicious and ferruginous matter. These are then introduced into a large porcelain tube, furnished with a prolongation and traversed by a current of hydrogen, dry and free from air. This tube being then heated to redness, the APC16.2NaCl distils without decomposition and condenses in the prolongation. There is found in the boats, after the operation, all the Al which had been reduced, collected in at most one or two small buttons. The boats when taken from the tube should be nearly free from Al C16.2NaCl and also from NaCl. The buttons of aluminium are united in a small earthen crucible which is heated as gently as possible, just sufficient to melt the metal. The latter is pressed together and skimmed clean by a small rod or tube of clay. The metal thus collected may be very suitably cast in an ingot mould."

The later precautions added to the above given process were principally directed towards avoiding the attacking of the crucible, which always takes place when the metal is melted with a flux, and the aluminium thereby made more or less siliceous. The next improvement was the introduction by