ance to the prolonged action of alkalies than the impure.

Mierzinski: Lime-water acts similarly to NaOH or KOH, with the difference that the resulting calcium compound is precipitated.

AQUA AMMONIA (NH1OH).

Deville: Aqua ammonia acts only feebly on aluminium, producing a little Al2O3, which, according to a very curious observation of Wöhler, has the property of partly dissolving in the ammonia. In an atmosphere in which ammonia was present, the metal did not lose its lustre, which is easily explained, because it is only in contact with water that the oxidization of the metal takes place, with disengagement of hydrogen.

ORGANIC ACIDS, VINEGAR, ETC.

Deville: Weak acetic acid acts on aluminium in the same way as H2SO4,. i. e., in an inappreciable degree or with extreme slowness. I used for the experiment acid diluted to the strength of strongest vinegar. M. Paul Morin left a plaque of the metal a long time in wine which contained tartaric acid in excess and acetic acid, and found the action on it quite inappreciable. The action of a mixture of acetic acid and NaCl in solution in pure water on pure aluminium is very different, for the acetic

acid replaces a portion of the HCl existing in the NaCl, rendering it free. However, this action is very slow on the Al, especially if it is pure.

The practical results flowing from these observations deserve to be clearly defined, because of the applications which may be made of aluminium to culinary vessels. I have observed that the tin so often used, and which each day is put in contact with NaCl and vinegar, is attacked much more rapidly than aluminium under the same circumstances. Although the salts of tin are very poisonous, and their action on the economy far from being negligible, the presence of tin in our food passes unperceived because of its minute quantity. Under the same circumstances, aluminium dissolves in less quantity; the acetate of Al formed resolves. itself on boiling into insoluble Al2O3 or an insoluble sub-acetate, having no more taste or action on the body than clay itself. It is for that reason, and because it is known that the salts of the metal have no appreciable action on the body, that aluminium may be considered as an absolutely harmless metal.

SOLUTIONS OF METALLIC SALTS.

Deville: The action of any salt whatever may be easily deduced from the action of the acids on the metal. We may, therefore, predict that in acid solutions of sulphates and nitrates aluminium will precipitate no metal, not even silver, as Wöhler has

observed. But the hydrochloric solutions of the same metals will be precipitated, as MM. Tissier have shown. Likewise, in alkaline solutions, Ag, Pb, and metals high in the classification of the elements are precipitated.

It may be concluded from this that to deposit aluminium on other metals by means of the battery, it is always necessary to use acid solutions in which HCl, free or combined, should be absent. For similar reasons the alkaline solutions of the same metals cannot be employed, although they give such good results in plating common metals with gold and silver. It is because of these curious properties that gilding and silvering aluminium are so difficult. M. Paul Morin and I have often tried a bath of basic sulphide of gold, or hyposulphite of silver, with a large excess of sulphurous acid, with no good results. But M. Mourey, who has already rendered great services in galvanoplasty, readily gilds and silvers aluminium for commerce with astonishing skill when we consider the short time he has had to study this question. I know also that M. Christofle has gilded it, but I am entirely ignorant of the processes employed by these gentlemen. The coppering of aluminium by the battery is effected very easily by means of M. Hulot's process. He uses simply a bath of acid sulphate of copper. The layer of copper, if well prepared, is very solid.

All that I have said on the subject of the action.

of metallic salts is true only for pure aluminium. Impure metal, especially if it contains iron or sodium, acts then in producing in the copper salts with which I operate a deposit of metallic Cu. But this phenomenon, even in the most unfavorable cases, is produced very slowly, and if a leaf of aluminium is used one may see at the end of several weeks the texture of the metal etched with red fibres, as if the Fe and Al were only in juxtaposition, and the ferruginous fibres acted alone. Moreover, the deposit is only local, and little by little becomes complete; but it is slower as the metal is purer.

Mierzinski: Silver is precipitated by Al from a nitrate solution, feebly acid or neutral, in dendrites; the separation begins after six hours; from an ammoniacal solution of AgCl or Ag2CrO4, Al precipitates the metal immediately as a crystalline powder.

From CuSO4 or Cu(NO3)2 solution, Al separates Cu only after two days, in dendrites or octahedra ; from the latter it also precipitates a basic salt as a green, insoluble powder; from a CuCl solution the Cu falls immediately; somewhat slower from solution of acetate of copper. The sulphate or nitrate solution behaves similarly if a little KCl is added to it, and the precipitation is complete in presence of excess of Al.

From Hg2Cl2, Hg2Cy2, and Hg2(NO3)2, Hg separates first, and then forms an amalgam with the Al which decomposes water at ordinary temperatures or oxidizes in the air with development of

much heat; the same qualities are possessed by the amalgam formed by warming the two metals together in an atmosphere of CO2.

From Pb(NO3)2 and Pb(C2H3O2) the metal separates slowly in crystals; from PbCl2 immediately; an alkaline solution of PbCrO1 gives Pb and Cr203.

From an alcoholic solution of HgCl2 the Hg is precipitated much quicker with a gentle heat. Al also reduces Hg from a solution of HgI2 in KI. Al separates Hg from HgCl2 vapors, and APC16 deposits in the cooler part of the tube, the remaining Al being melted by the heat of the reaction. Al acts likewise toward melted AgCl, the silver set free being melted by the heat of the reaction. Zn is easily thrown down from alkaline solution.

Fremy: Aluminium decomposes a very large number of metallic solutions, which takes place especially easily if the solution is made alkaline or ammoniacal. Acid, and especially neutral solutions, are less favorable for the experiment. All the chlorides, excepting KCl and NaCl, are reduced by it. Al2C1 is no exception, for the solution is decomposed with evolution of hydrogen. Aluminium easily resists solutions of NaCl and alum separately, but dissolves in a mixed solution of these two salts. In alkaline solution, the metals are precipitated because of the facility with which aluminates of the alkalies are formed.

Watts (2d Supplement): The action of aluminium on metallic solutions is as follows: Cu is pre