Coating With Platinum

This metal has never yet been successfully deposited as a protecting coating to other metals. A solution may be made by dissolving it in a mixture of nitric and muriatic acids, the same as is employed in dissolving gold; but heat must be applied. The solution is then evaporated to dryness, and to the remaining mass is added a solution of cyanide of potassium; next, it must be slightly heated for a short time, and then filtered This solution, evaporated, yields beautiful crystals of cyanide of platinum and potassium; but it is unnecessary to crystallize the salt. A very weak battery power is required to deposit the metal: the solution should be heated to 100°. Great care must be taken to obtain a fine metallic deposit: indeed the operator may not sue ceed once in twenty times in getting more than a mere coloring of metal over the surface, and that not very adhesive. The causes of the difficulty are probably these: the platinum used as an electrode is not acted upon; the quantity of salt in solution is very little; it requires a particular battery strength to gives a good deposit, and the slightest strength beyond this gives a black deposit; so that, were the proper relations obtained, whenever there is any deposit, the relations of battery and solution are changed, and the black pulverulent deposit follows.

We have occasionally succeeded in obtaining a bright metallic deposit of platinum, possessing the qualities of adhesion and durability: some of the articles thus covered presented no signs of change after many years: but we have never been so fortunate as to get a platinum deposit that could protect any metal from the action of acids, or other fluids by which the metal could be affected. We have covered iron, such as the end of a glass-blower's blowpipe, so that it could be made red-hot without the iron rusting, but rather taking the characteristic appearance of platinum: but even that did not protect the iron from rusting when it was put a short time into water, or kept exposed to moist air. We have seen again and again recommendations of certain solutions of platinum for the purpose of obtaining a reguline metal, and no doubt it has been obtained, but, as stated above, we believe more incidentally than at will. The protoxalate of platinum has been strongly recommended for covering copper and brass with platinum.*

Coating With Palladium

Palladium is a metal very easily deposited. The solution is prepared by dissolving the metal in nitro-muriatic acid, and evaporating the solution nearly to dryness; then adding cyanide of potassium till the whole is dissolved: the solution is then filtered and ready for use. The cyanide of potassium holds a large quantity of this metal in solution, and the electrode is acted upon while the deposit is proceeding. Articles covered with this metal assume the appearance of the metal; but so far as we are aware, it has not yet been applied to any practical purpose. It requires rather a thick deposit to protect metals from the action of acids, which is, probably, the only use it can be applied to.

Coating With Nickel

Nickel is very easily deposited; and may be prepared for this purpose by dissolving it in nitric acid, then adding cyanide of potassium to precipitate the metal; after which the precipitate is washed and dissolved by the addition of more cyanide of potassium. Or the nitrate solution may be precipitated by carbonate of potash; this should be well washed, and then dissolved in cyanide of potassium; a proportion of. carbonate of potash will be in the solution, which we have not found to be detrimental. This latter method of preparing the nickel plating solution is simple, and, therefore, has our recommendation. The metal is very easily deposited; it yields a color approaching to silver, which is not liable to tarnish on exposure to the air. A coating of this metal would be very useful for covering common work such as gasaliers, and other gas-fittings, and even common plate. The great difficulty experienced is to obtain a positive electrode: the metal is very difficult to fuse, and so brittle that we have never been able to obtain either a plate or a sheet of it. Could this difficulty be easily overcome, the application of nickel to the coating of other metals would be extensive, and the property of not being liable to tarnish would make it eminently useful for all general purposes. We coated articles with nickel in 1845, which were exposed to the air for many years without tarnish, and when last seen by the author exhibited no change.

* Polyteohni. Coustuh. 1855.

Antimony, Arsenic, Tin, Iron, Lead, Bismuth, And Cadmium

We have deposited these metals from their solutions in cyanide of potassium; but not for any useful application.

Iron

Iron may be very easily deposited from its sulphate: dissolve a little crystalline sulphate of iron in water, and add a few drops of sulphuric acid to the solution: one pair of Smee's battery may be used to deposit the iron upon copper or brass. The metal in this pure state has a very bright and beautiful silver color.

Lead

Lead may be deposited from a solution of an acid salt, . such as the acetate, but requires some management or strength of battery: it may also be deposited from its solution in potash or soda.