chlorhydrate of alumina, whose composition is not known, and which is soluble in water. When the metal thus tarnishes in water one may be sure to find chlorine in the water on testing it with nitrate of silver.

Mierzinski: Cold and warm water have no influence on aluminium even if it is heated to redness.

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'Chemical News,' 1859: Aluminium leaf will slowly decompose water at 100°; at first it takes a bronze color, and after boiling some hours it becomes translucent.

ACTION OF HYDROGEN SULPHIDE AND SULPHUR
(H'S and S).

Deville: Sulphuretted hydrogen exercises no action on aluminium, as may be proved by leaving the metal in an aqueous solution of the gas. In these circumstances almost all the metals, and especially silver, blacken with great rapidity. Sulph-hydrate of ammonia may be evaporated on an aluminium leaf, leaving on the metal only a deposit of sulphur which the least heat drives

away.

Aluminium may be heated in a glass tube to a red heat in vapor of sulphur without altering the metal. This resistance is such that in melting together polysulphide of potassium and some aluminium containing copper or iron, the latter are

attacked without the aluminium being sensibly affected. Unhappily, this method of purification may not be employed because of the protection which aluminium exercises over foreign metals. Under the same circumstances gold and silver dissolve up very rapidly. However, at a high temperature I have observed that it combines directly with sulphur to give A12S3. These properties varying Al2S3. so much with the temperature form one of the special characteristics of the metal and its alloys.

Fremy H2S is without action on aluminium, acting towards it as towards the sulphides of iron, zinc, or copper. It is true that aluminium decomposes Ag2S, but it sets the sulphur at liberty and combines with the silver. These facts are in accordance with the resistance the metal offers to free sulphur.

SULPHURIC ACID (H2SO4).

Deville Sulphuric acid, diluted in the proportion most suitable for attacking the metals which decompose water, has no action on aluminium; and contact with a foreign metal does not help, as with zinc, the solution of the metal, according to M. de la Rive. This singular fact tends to remove aluminium considerably from those metals. To establish it better, I left for several months some globules weighing only a few milligrammes in contact with weak H2SO4, and they showed no visible

alteration; however the acid gave a faint precipitate with aqua ammonia.

Fremy: H2SO1, dilute or concentrated, exercises in the cold only a very slight sensible action on aluminium, the pure metal is attacked more slowly than when it contains foreign metals. The presence of silicon gives rise to a disengagement of Sill', which communicates to the hydrogen set free a tainted odor. Concentrated II2SO1 dissolves it rapidly with the aid of heat, disengaging sulphurous acid gas (SO2).

NITRIC ACID (HNO3).

Deville: Nitric acid, weak or concentrated, does not act on aluminium at the ordinary temperature. In boiling HNO3 the solution takes place, but with such slowness that I had to give up this mode of dissolving the metal in my analyses. By cooling the solution all action ceases. M. Hulot has obtained good results on substituting aluminium for platinum in the Grove battery.

HYDROCHLORIC ACID (HCl).

Deville: The true solvent of aluminium is HCl, weak or concentrated; but, when the metal is perfectly pure, the reaction takes place so slowly that M. Favre, of Marseilles, had to give up this way of attack in determining the heat of a combination of

the metal. But impure aluminium is dissolved very rapidly. At a very low temperature gaseous HCl attacks the metal and changes it into Al2C1o. Under these circumstances iron does not seem to alter; able, no doubt, to resist by covering itself with a very thin protecting layer of FeCl2. This experiment would lead me to admit that it is the HC and not the water which is decomposed by aluminium; and, in fact, the metal is attacked more easily as the acid is more concentrated. This explains the difference of the action of solutions of HCl and H2SO4, the latter being almost inactive. This reasoning applies also to tin.

When the metal contains silicon, it disengages hydrogen of a more disagreeable smell than that given out by iron under similar circumstances. The reason of this is the production of that remarkable body recently discovered by MM. Wöhler and Buff-SiH1. When the proportion of silicon is small, the whole is evolved as gas; when increased a little, some remains in solution with the aluminium, and then it requires great care to separate the metal exactly, even when the solution is evaporated to dryness. If 3 to 5 per cent. of Si is present, it remains insoluble mixed with a little SiO2, as has been cleverly proven by Wöhler and Buff by the action of hydrofluoric acid, which dissolves the SiO2 with evolution of H without attacking the Si itself. On dissolving commercial aluminium there is sometimes obtained a black,

crystalline residue, which, separated on a filter and dried at 200° to 300° takes fire in places; this residue is Si mixed with some SiO2. The presence of Si augments very much the facility with which Al is attacked by HCl.

Mierzinski: If HCl is present in a mixture of acids, it begins the destruction of the metal. III, HBr, and HF act similarly to HCl.

POTASH, SODA, AND LIME (KOH, NaOH, Ca(OH)2).

Deville: Alkaline solutions act with great energy on the metal, transforming it into aluminate of potash or soda, setting free hydrogen. However, it is not attacked by KOH or NaOH in fusion; one may, in fact, drop a globule of the pure metal into melted caustic soda raised almost to a red heat in a silver vessel, without observing the least disengagement of hydrogen. Silicon, on the contrary, dissolves with great energy under the same circumstances. I have employed melted NaOH to clean siliceous aluminium. The piece is dipped into melted NaOH kept almost at red heat. At the moment of immersion several bubbles of II disengage from the metallic surface, and when they have disappeared, all the Si of the superficial layer of Al has been dissolved. It only remains to wash well with water and dip it into nitric acid, when the aluminium takes a beautiful mat.

Mallet: The pure metal presents greater resist