Mierzinski: No less remarkable than the conductivity of aluminium for electricity is that for heat. According to Calvert and Johnson (Dingler, 153, 285), that of silver being 1000, aluminium is 665.

SPECIFIC HEAT.

Deville: According to the experiments of M. Regnault, the specific heat of aluminium corresponds to its equivalent 13.75, from which we may conclude that it must be very large when compared with all the other useful metals. One can easily perceive this curious property by the considerable time which it takes an ingot of the metal to get cold. We might even suggest that a plate of aluminium would make a good chafing dish. Another experiment makes this conclusion very evident. M. Paul Morin had the idea to use aluminium for a plate on which to cook eggs, the sulphur of which attacked silver so easily; and he obtained excellent results. He noticed, also, that the plate kept its heat a much longer time than the silver one. This exceptional property should be utilized for something.

Mallet: The specific heat of absolutely pure aluminium was 0.2253, therefore the atomic heat is 0.2253 times 27.02 or 6.09.

Fremy: The specific heat of aluminium is

0.2181; larger than that of any other useful metal, which accords with its small atomic weight.

MAGNETISM.

Deville: I have found, as also MM. Poggendorff and Reiss, that aluminium is very feebly magnetic.

CRYSTALLINE FORM.

Deville: Aluminium often presents a crystalline appearance when it has been cooled slowly. When it is not pure the little crystals which form are needles, and cross each other in all directions. When it is almost pure it still crystallizes by fusion, but with difficulty, and one may observe on the surface of the ingots hexagons which appear regularly parallel along lines which centre in the middle of the polygon. It is an error to conclude from this observation that the metal crystallizes in the rhombohedral system. It is evident that a crystal of the regular system may present a hexagonal section; while, on the other hand, in preparing aluminium by the battery at a low temperature, I have observed complete octahedrons, which were impossible of measurement, it is true, but their angles appeared equal.

PART IV.

CHEMICAL PROPERTIES OF ALUMINIUM.

REMARK: Unless specifically stated otherwise, the properties here mentioned are those of the pure metal and not of the commercial, the impurities of which generally modify the properties of the aluminium more or less.

ACTION OF AIR.

Deville: Air, wet or dry, has absolutely no action on aluminium. No observation which has come to my knowledge is contrary to this assertion, which may easily be proved by any one. I have known of beams of balances, weights, plaques, polished leaf, reflectors, etc., of the metal exposed for months to moist air and sulphur vapors, and showing no trace of alteration. We know that aluminium may be melted in the air with impunity. Therefore air and also oxygen cannot sensibly affect it; it resisted oxidation in the air at the highest heat I could produce in a cupel furnace, a heat much higher than that required for the assay of gold. This experiment is interesting, especially

when the metallic button is covered with a layer of oxide which tarnishes it, the expansion of the metal causes small branches to shoot from its surface, which are very brilliant, and do not lose their lustre in spite of the oxidizing atmosphere. M. Wöhler has also observed this property on trying to melt the metal with a blowpipe. M. Peligot has profited by it to cupel aluminium. I have seen buttons of impure metal cupelled with lead and become very malleable.

With pure aluminium the resistance of the metal to direct oxidation is so considerable that at the melting point of platinum it is hardly appreciably touched, and does not lose its lustre. It is well known that the more oxidizable metals take this property away from it. But silicon itself, which is much less oxidizable, when alloyed with it makes it burn with great brilliancy, because there is formed a silicate of aluminium.

Watts: Aluminium may be heated intensely in a current of air in a muffle without undergoing more than superficial oxidation. When heated as foil with a splinter of wood in a current of oxygen it burns with a brilliant, bluish-white light.

'Chemical News,' 1859: Wöhler finds that aluminium leaf burns brightly in air and in oxygen with a brilliant light. The Al2O3 formed is as hard as corundum. Wire burns in oxygen like iron wire, but the combustion cannot continue because the wire fuses.

Mierzinski: Aluminium does not change at a somewhat high temperature in the air; but if heated to whiteness it burns, with the production of strong light, to Al2O3, which covers the surface of the bath.

ACTION OF WATER (II2O).

Deville: Water has no action on aluminium, either at ordinary temperatures, or at 100°, or at a red heat bordering on the fusing point of the metal. I boiled a fine wire in water for half an hour and it lost not a particle in weight. The same wire was put in a glass-tube heated to redness by an alcohol lamp and traversed by a current of steam, but after several hours it had not lost its polish, and had the same weight. To obtain any sensible action it is necessary to operate at the highest heat of a reverberatory furnace, a white heat. Even then the oxidation is so feeble that it develops only in spots, producing almost inappreciable quantities of Al2O3. This slight alteration and the analogies of the metal allow us to admit that it decomposes water, but very feebly. however, metal produced by M. Rose's method was used, which is almost unavoidably contaminated with slag composed of chlorides of aluminium and sodium, the Al2C1, in presence of water, plays the part of an acid towards aluminium, disengaging hydrogen with the formation of a sub

If,