tools of the same metal are used, which facilitate at the same time the fusion of the solder and its adhesion to the previously prepared surfaces. Tools of copper or brass must be strictly avoided, as they would form colored alloys with the aluminium and the solder. The use of the little tools of aluminium is an art which the workman must acquire by practice. At the moment of fusion the work needs the application of friction, as the solder suddenly melts very completely. In soldering it is well to have both hands free and to use only the foot for the blowing apparatus. The solders used are of aluminium, copper, and zinc. (See the ones given by Kerl & Stohman, p. 250.) No. IV. is the one generally preferred, particularly for small objects. In order to make the solder, the copper is first melted, the aluminium added, and the whole stirred with an unpolished iron rod, just as it comes from the forge, adding also a little tallow. The zinc is then added, avoiding too much heat, which would drive it off. In soldering, also, too high a heat should be avoided for the same reason.

VENEERING WITH ALUMINIUM.

Deville is the first writer to make mention of this art :

"M. Sevrard succeeded in 1854 in plating aluminium on copper and brass with great perfection. The two metallic surfaces being prepared in the

ordinary manner and well scoured with sand, they are placed one on the other and held tightly between two iron plates. The packet is then heated to dark redness, at which temperature it is strongly compressed. The veneer becomes very firmly attached, and sheets of it may be beaten out. I have a specimen of such work perfectly preserved. The delicate point of the operation is to just heat the packet to that point that the adherence may be produced without fusing the aluminium, for when it is not heated quite near to this fusing point, the adherence is incomplete. Experiments of this kind with copper and aluminium foil did not succeed, for as soon as any adherence manifested itself the two metals combined and the foil disappeared into the copper. In an operation made at too low a temperature, the two metals, as they do not behave similarly on rolling, become detached after a few passes through the rolls. Since then, the experiments in veneering aluminium on copper, with or without the intervention of silver, have succeeded very well."

The only other article to be found on this subject is Dr. Clemens Winckler's paper, from which we extract the following *

-

"The question demands attention whether it is not possible to coat certain metals and alloys with aluminium, and thereby impart to them, superfi

*Industrie Blätter, 1873.

cially at least, the advantageous properties of that metal. The present high price of the metal does not stand in its way for this purpose; and it only remains now to decide whether it is practicable to coat our common metals, iron, copper, etc., with it. The question must at present be answered in the negative. Two methods can be used for covering one metal with another, galvanoplasty and plating or veneering. The separation of aluminium by the galvanic current succeeds only by the use of a bath of molten anhydrous AlC16.2NaCl, melting at 165° C. (329° F.), but the metal is deposited as a non-coherent powder, mixed with NaCl, and therefore the object of plating is not attained in this way. No one has yet been able to throw down aluminium in a metallic state from aqueous solution, and it was an error when Gore stated that he had coated copper with aluminium by means of a solution of Al2C16 in water and a weak galvanic current. Concerning the coating of metals by the so-called plating method, it is indeed, according to my own experience, possible to a certain degree, but the product is entirely useless, every plating requiring an incipient fusing of both metals and their final intimate union by rolling. The ductility of aluminium is, however, greatly injured by even a slight admixture with other metals; iron makes it brittle and copper, in small per cent. makes it fragile as glass. If now it were possible in any way to fuse a coating of aluminium upon another metal, there would be

formed an intermediate alloy between the two metals from which all ductility would be gone and which would crumble to powder under the pressure of the rolls, thus separating the aluminium surface from the metal beneath. But even if it were possible in this way to coat a metal with a thin plate, it is still doubtful if anything would be attained thereby. For, while compact aluminium resists oxidizing and sulphurizing agencies, the divided metal does not. In powder or leaves aluminium is readily oxidized, as is shown by its amalgam becoming heated in the air and quickly forming alumina. In the form of a coating upon other metals it must necessarily be in a somewhat finely divided state, and hence would probably lose its durability."

GILDING AND SILVERING ALUMINIUM.

Deville says: "The gilding and silvering of aluminium by electricity is very difficult to do satisfactorily and obtain the desirable solidity. M. Paul Morin and I have often tried it by using a bath of acid sulphide of gold or of nitrate of silver with an excess of sulphurous acid. Our success has only been partial. However, M. Mourey, who has already rendered great services in galvanoplasty, gilds and silvers the aluminium of commerce with a surprising perfection considering the little time he has had to study the question. I also know that Mr. Christofle has gilded it, but I

am entirely ignorant of the methods employed by these gentlemen."

Watts's Dictionary: "Eight grammes of gold are dissolved in aqua regia, the solution diluted with water and left to digest twenty-four hours with an excess of lime. The precipitate, with the lime, is well washed, and then treated with a solution of twenty grammes of hyposulphate of soda. The liquid resulting serves for the gilding of aluminium without the aid of heat or electricity, the metal being simply immersed in it after being previously well cleaned by the successive use of caustic potash, nitric acid, and pure water."

Kerl and Stohman: "Gilding and silvering aluminium galvanically does not offer the least difficulty. One can, by using a proper ground, coat it with silver and gold in six different colors, by employing the correct combination, such as shining or matt gold and silver or lead gray."

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