REDUCTION FROM CRYOLITE.

We will here give H. Rose's entire paper, as an account of this eminent chemist's investigations written out by himself with great detail, describing failures as well as successes, cannot but be of value to all interested in the production of aluminium.*

"Since the discovery of aluminium by Wöhler, Deville has recently devised the means of procuring the metal in large, solid masses, in which condition it exhibits properties with which we were previously unacquainted in its more pulverulent form as procured by Wöhler's method. While, for instance, in the latter state it burns vividly to white earthy alumina on being ignited, the fused globules may be heated to redness without perceptibly oxidizing. These differences may be ascribed to the greater amount of division on the one hand and of density on the other. According to Deville, however, Wöhler's metal contains platinum, by which he explains its difficulty of fusion, although it affords white alumina by combustion. Upon the publication of Deville's researches I also tried to produce aluminium by the decomposition of Al C16.2NaCl by means of sodium. I did not, however, obtain satisfactory results. Prof. Rammelsberg, who followed

* Pogg. Annalen, Sept. 1855. .

Moreover, exactly the

method of Deville, obtained but a very small product, and found it very difficult to prevent the cracking of the glass-tube in which the experiment was conducted by the action of the vapor of sodium on Al2C16. It appeared to me that a great amount of time, trouble, and expense, as well as long practice, was necessary to obtain even small quantities of this remarkable metal.

"The employment of AlCl and its compounds with alkali chlorides is particularly inconvenient, owing to their volatility, deliquescence, and to the necessity of preventing all access of air during their treatment with sodium. It very soon occurred to me that it would be better to use the fluoride of aluminium instead of the chloride; or rather the combination of the fluoride with alkaline fluorides, such as we know them through the investigations of Berzelius, who pointed out the strong affinity of A12F6 for NaF and KF, and that the mineral occurring in nature under the name of Cryolite was a pure compound of A12F6 and NaF.

"This compound is as well fitted for the preparation of aluminium by means of sodium as A12C16 or Al2C16.2NaCl. Moreover, as cryolite is not volatile, is readily reduced to the most minute state of division, is free from water and does not attract moisture from the air, it affords peculiar advantages over the above-mentioned compounds. In fact, I succeeded with much less trouble in preparing aluminium by exposing cryolite together with

sodium to a strong red heat in an iron crucible, than by using Al2Clo and its compounds. But the scarcity of cryolite prevented my pursuing the experiments. In consequence of receiving, however, from Prof. Krantz, of Bonn, a considerable quantity of the purest cryolite at a very moderate price ($2 per kilo), I was enabled to renew the investigation.

"I was particularly stimulated by finding, most unexpectedly, that cryolite was to be obtained here in Berlin commercially at an inconceivably low price. Prof. Krantz had already informed me that cryolite occurred in commerce in bulk, but could not learn where. Shortly after, M. Rudel, the manager of the chemical works of H. Kunheim, gave me a sample of a coarse white powder, large quantities of which were brought from Greenland, by way of Copenhagen, to Stettin, under the name of mineral soda, and at the price of $3 per centner. Samples had been sent to the soap boilers, and a soda-lye had been extracted from it by means of quicklime, especially adapted to the preparation of many kinds of soap, probably from its containing alumina. It is a fact, that powdered cryolite is completely decomposed by quicklime and water. The fluoride of lime formed contains no alumina, which is all dissolved by the caustic soda solution; and this, on its side, is free from fluorine, or only contains a minute trace. I found this powder to be of equal purity to that received from Prof.

www.

Krantz. It dissolved without residue in HCI (in platinum vessels); the solution evaporated to dryness with H2SO4, and heated till excess of acid was dissipated, gave a residue which dissolved completely in water, with the aid of a little HCl. From this solution, ammonia precipitated a considerable quantity of alumina. The solution filtered from the precipitate furnished, on evaporation, a residue of sulphate of soda, free from potash. Moreover, the powder gave the well-known reactions of fluorine in a marked degree. This powder was cryolite of great purity: therefore the coarse powder I first obtained was not the form in which it was originally produced. It is now obtainable in Berlin in great masses; for the preparation of aluminium it must, however, be reduced to a very fine powder.

"In my experiments on the preparation of aluminium, which were performed in company with M. Weber, and with his most zealous assistance, I made use of small iron crucibles, 1 inches high and 13 inches upper diameter, which I had cast here. In these I placed the finely divided cryolite between thin layers of sodium, pressed it down tight, covered with a good layer of potassium chloride (KCl), and closed the crucible with a wellfitting porcelain cover. I found KCl the most advantageous flux to employ; it has the lowest specific gravity of any which could be used, an important point when the slight density of the

metal is taken into consideration. It also increases the fusibility of the sodium fluoride. I usually employed equal weights of cryolite and KCl, and for every five parts of cryolite two parts of sodium. The most fitting quantity for the crucible was found to be ten grammes of powdered cryolite. The whole was raised to a strong red heat by means. of a gas-air blowpipe. It was found most advantageous to maintain the heat for about half an hour, and not longer, the crucible being kept closely covered the whole time; the contents were then found to be well fused. When quite cold the melted mass is removed from the crucible by means of a spatula, this is facilitated by striking the outside with a hammer. The crucible may be employed several times, at last it is broken by the hammer blows. The melted mass is treated with water, when, at times only, a very minute evolution of hydrogen gas is observed, which has the same unpleasant odor as the gas evolved during solution of iron in HCl. The carbon contained in this gas is derived from a very slight trace of naphtha adhering to the sodium after drying it. On account of the difficult solubility of NaF, the mass is very slowly acted on by water, although the insolubility is somewhat diminished by the presence of the KCl. After twelve hours the mass is softened so far that it may be removed from the liquid and broken down in a porcelain mortar. Large globules of aluminium are then discovered,