So then, within the limits usually found in commercial aluminium, i. e., silicon less than 5 per cent. and iron anywhere less than 10 per cent., a careful determination of the sp. gr. should, by a little calculation, give the amount of iron present within a limit of error of 0.5 per cent. at most, thus saving a wet determination of iron. AMALGAMATION OF ALUMINIUM. Wishing to observe the effect of mercury on metallic aluminium, I took a clean, bright piece of aluminium foil of Mr. Frishmuth's make, and put on it a small globule of mercury, which I rubbed in with the finger. Almost immediately a white powder appeared and the foil felt warm from the heat generated. On brushing away this powder, the foil underneath appeared white and unattacked. By letting the mercury remain on the foil, it very soon eat a hole through it. Compare with p. 261. It thus appears that mercury unites with a clean surface of aluminium, forming an amalgam, and the aluminium in the amalgam oxidizes in the air to alumina. The question arises, why does aluminium oxidize so easily? We know how the properties of this metal depend much on its state of division; its foil will burn in the air, whereas the metal in bulk will not. The mercury serves, as it amalgamates the aluminium, to draw apart even the molecules of the metal, and so this extremely minute, even molecular division of the aluminium permits it to exhibit in an intensified degree the principle just stated, which was illustrated by the burning of the foil, i. e., the finer its state of division the more easily is it acted on by oxidizing agents. Translating this into the language of chemical affinities, in metallic aluminium the atoms are united two by two by a mutual exchange of affinities, and the oxygen of the air is not able to break this molecular bond at ordinary temperatures. But by the intervention of the mercury this bond is broken, and the atoms of aluminium become united with atoms of mercury, which weakens the bond holding the molecule together. The strong affinity which oxygen has for aluminium is now able to break up the new molecule, the metal is rapidly oxidized and the mercury set free. REDUCTION OF ALUMINA. I experimented on reducing alumina by carbon in presence of copper. (See p. 213.) I took for a charge— 40 grms. 5 5 66 66 CuO and Cu. Charcoal. These were intimately mixed and finely powdered, put in a white-clay crucible and covered with cryolite. The whole was slowly heated to bright redness, and kept there for two hours. A bright button was found at the bottom of the crucible. This button was of the same sp. gr. as pure copper, and a qualitative test showed no trace of aluminium in it. This is the same result that other experimenters have reached, and the conclusion seems to be that the process gives no practical results. PRODUCTION AND REDUCTION OF ALUMINIUM Until the researches of M. Fremy, no other method of producing Al'S3 was known save by acting on the metal A with sulphur at a very high heat. Fremy was the first to open up this new field, and it may be that his discoveries will yet be the basis of successful industrial processes. Fremy is often quoted in connection with A12S3, and in order to understand just how much he discovered we here give all that his original paper contains concerning this sulphide.* "We know that sulphur has no action on silica, boric oxide, magnesia, or alumina. I thought that it might be possible to replace the oxygen by sulphur if I introduced or intervened a second affinity, as that of carbon for oxygen. These decompositions produced by two affinities are very frequent in chemistry, it is thus that carbon and chlorine, by acting simultaneously on silica or alumina, produce silicon or aluminium chloride, while either alone could not decompose it; a similar case is the decomposition of chromic oxide by carbon bisulphide, producing chromium sesquisulphide. Reflecting on these relations, I thought that carbon bisulphide ought to act at a high heat on silica, magnesia, and alumina, producing easily their sulphides. Experiment has confirmed this view. I have been able to obtain in this way almost all the sulphides which until then had been produced only by the action of sulphur on the metals. "To facilitate the reaction and to protect the sulphide from the decomposing action of the alkalies contained in the porcelain tube which was used, I found it sometimes useful to mix the oxides with carbon and to form the mixture into bullets resembling those employed in the preparation of Al2C16. I ordinarily placed the bullets in little * Ann. de Chem. et de Phys. [3] xxxviii. 312. carbon boats, and heated the tube to whiteness in the current of vaporized carbon bisulphide. The presence of divided carbon does not appear useful in the preparation of this sulphide. "The A12S formed is not volatile; it remains in the carbon boats and presents the appearance of a melted vitreous mass. On contact with water it is immediately decomposed. Al2S3+3H2O=Al2O3+3H2S. "The alumina is precipitated, no part of it going into solution. This precipitated AO3 is immediately soluble in weak acids. The clear solution, evaporated to dryness, gives no trace of alumina. It is on this phenomenon that I base a method of analysis as will be seen below. "Analysis of the product. Al2S3 being non-volatile, it is always mixed with some undecomposed alumina. It is, in fact, impossible to entirely transform all the alumina into A12S3. I have heated less than a gramme of alumina to redness five or six hours in carbon bisulphide vapor, and the product was always a mixture of Al'O3 and Al2S3. The reason is that the sulphide being non-volatile and fusible coats over the alumina and prevents its further decomposition. The Al2O3 thus mixed with the A12S3, and which has been exposed to a red heat for a long time, is very hard, scratches glass, and is in grains which are entirely insoluble in acids. By reason of this property I have been able to analyze the product exactly, for on treating the product with water and determining on the one hand the sulphuretted hydrogen evolved, and on the other the quantity of soluble alumina resulting, I have determined the two elements of the compound. One gramme of my product contained 0.365 grm. of Al2S3, or 36.5 per cent., the remainder being undecomposed alumina." The com The above is the substance of Fremy's remarks on A12S3. The next investigation in this field was made by Reichel. His paper is on the sulphides of magnesium and aluminium and he proceeded in methods so similar with both metals that he sometimes describes a process only for magnesium sulphide, MgS, with details, and merely states his results in working the same way for Al2S3, which will account for the frequent allusion in his paper to MgS. The paper is very lengthy, but only what bears directly on the subject in hand is extracted. "I wished to obtain more definite knowledge of MgS and Al2S3, and I also had a practical end in view; for, depending on the small affinity of sulphur for magnesium and aluminium, I hoped, if not to isolate them from the sulphide, at least to try the possibilities of this method." (As preliminary, Reichel here gives extended remarks on the behavior of aluminium and magnesium towards sulphur, and a description of the sulphides.) "Al2S3 appears yellow, at least that made from the metal and sulphur with exclusion of air always has this * Jrnl. fr. Prak. Chem. xii. 55. |