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color and lustre identical with those of platinum articles found in the arts.

One part of finely laminated platinum (platinum-sponge is preferable) is covered in a long-necked glass flask with a mixture of 15 parts of hydrochloric acid and 10 parts of nitric acid of 40° Baumé. It is then heated upon a plate of perforated sheet-iron, so that the bottom of the flask. alone receives the heat. An abundant disengagement of orange-yellow fumes ensues, and the platinum disappears, leaving a reddish liquid, which should be heated until it becomes viscous enough to adhere to the sides of the flask. This latter part of the operation may be effected in a porcelain evaporating dish, the shallow form of which hastens the evaporation of the excess of acids. After cooling, the residuum is dissolved in 50 parts of distilled water, and, if necessary, filtered.

In a separate vessel, 10 parts of phosphate of ammonium are dissolved in 50 parts of distilled water, and the two solutions are mixed. A copious precipitate of phosphate of ammonium and platinum is formed in a liquid of orange color, which should not be separated, and into which should be poured, with constant stirring, another solution, composed of 50 parts phosphate of sodium in 100 parts. of distilled water.

The mixture is made to boil, and the evaporated water is replaced, until no more ammonia is disengaged (which is ascertained by the smell), and until the liquid, which was previously alkaline, begins to redden blue litmus. paper. By the reactions which take place, the previously yellow liquid becomes colorless, which indicates the forma tion of a double salt of sodium and platinum.

The solution is then ready to deposit platinum upon articles of copper, or its alloys; it is used hot, and with a strong electrical current. A platinum anode is used, but

as this is not dissolved by the solution the metallic strength of the bath must be maintained by occasional additions of the chloride of platinum.

Roseleur affirms that copper capsules thus coated with platinum resisted twenty successive evaporations of nitric and sulphuric acids alternately employed, though at last they were corroded.

According to the same authority, it is necessary to avoid with great care the contact of iron, zinc, lead, or tin with the bath, as these metals will decompose it, that is to say, platinize themselves by simple immersion, and the deposited metal will be black and pulverulent.

Dead-platinizing is pearl-gray; it is very hard, and cannot be brightened by scratch-brushes of brass, which render its surface yellow. Iron brushes, or, preferably, powdered pumice-stone, should be employed.

Platinum deposits may be burnished by energetic friction, and the lustre obtained is very durable.

As most platinized articles, such as chandeliers, fire grates, lamps, etc., are very lightly platinized, they are generally polished before coating. After the operation, they are rubbed with polishing rouge and chamois, whereby the difficulty of burnishing the platinum itself is avoided.

Platinum may be removed from copper by a very long immersion in the baths indicated for ungilding, but the operation is not always successful.

Other Formulæ.

Boettger (Pharmaceutical Journal, iii. 351) coats copper and brass with platinum as follows: he dissolves the double chloride of platinum and ammonium in water, adds thereto a few drops of ammonia, and uses the solu tion thus prepared, moderately heated, and with a con

stant current. The deposited The deposited platinum is said to be adhe

rent and lustrous.

Another solution of Boettger's for platinizing copper and brass either by simple immersion or by the current, consists of one part of double chloride of platinum and ammonium, and eight parts of sal ammoniac in water. The same author (The Polytechnic Review, vi. 255) recommends the following solution for obtaining electro-deposits of platinum. He treats freshly precipitated double chloride of platinum and ammonium, at boiling temperature, with a concentrated solution of the neutral citrate of sodium. The resulting liquid has a deep orange-red color, and a feeble acid reaction, and yields with a current of moderate intensity an adherent, lustrous coating of platinum.

Gore (Electro-Metallurgy, 120) refers to a solution made by dissolving the chloride of platinum in one of cyanide of potassium, the proportion of metal being kept at about one ounce to the gallon, and the bath used with a moderate current and warm. Jewreinoff prepares a solution for the electro-deposition of platinum on copper, brass, and iron as follows: Convert 10 parts of metallic platinum into chloride, and add thereto a solution of 10 parts caustic potassa in water. Dissolve the yellow precipitate by the addition of 20 parts of oxalic acid in aqueous solution, with the aid of heat, and add to the solution 30 parts of caustic potassa solution. The solution is strongly alkaline (soda may be substituted for potassa in this formula). A constant and moderate current is recommended, and Jewreinoff affirms that a platinum anode is dissolved in this liquid in the same proportion as platinum is deposited, so that the metallic strength of the bath is maintained without additions of platinum salt. This assertion we have had no opportunity to verify, but we

regard it as questionable. Gore, referring to similarly constituted solutions, says that it is difficult to obtain reguline white metal from them.

For platinizing sheets of silver Jewreinoff (Winckler, Handb. d. Metallüberzügen, 215) converts 3 parts of platinum into chloride, dissolves this in 300 parts of distilled water, and adds 20 to 25 parts of sulphuric acid. By using a platinum anode, the silver sheets soon accept a grayish coating of platinum, which simply requires to be washed.

A method of platinizing by contact with zinc, which is described as well suited for small articles is as follows (Chemical News, xix. 226): To a strong solution of platinic chloride, add powdered carbonate of sodium, until effervescence has ceased. Then add some glucose, and finally add enough common salt to cause a whitish precipitate. The small articles of copper or brass, to be coated, are placed in a colander of zinc, and immersed in the bath, kept at about 140° Fahr., for a few seconds. They are then removed, and dried in hot sawdust.

The deposition of platinum is attended with special difficulties, both on account of the non-solubility of the anode, which requires the operator to be adding fresh platinum salt from time to time where a solid deposit is desired; and also because of the disposition of the metal to give a black and pulverulent deposit. Roseleur's procedure is admitted to be the best that has thus far been devised for deposits of any thickness; and the citrate bath of Boettger is highly spoken of by those who have had occasion to use it.

Palladium, which belongs to the same group of metals as platinum, has also been experimented with as a coating for other metals. It appears to be more readily deposited from its solutions by the current.

For obtaining deposits of this metal, solutions have been made by dissolving the chloride in cyanide of potassium, or by saturating a solution of the cyanide of potassium with the metal, by the current, in the manner described with gold and silver. Cyanide of potassium appears to take up a considerable quantity of the metal, and the cyanide solution is said to yield the metal freely, so that heavy reguline deposits are not very difficult to - obtain.

Bertrand (Comptes Rendus, tome. lxxxiii., 857) describes the double chloride of palladium and ammonium, perfectly neutral, as a good solution with which to obtain palladium deposits, either by immersion or by the current. An anode of palladium is dissolved, while the deposit is going on. Palladium, however, is one of the rarer metals; it does not protect other metals as well as platinum, and its behavior is therefore of no practical importance.

We had the opportunity, while this work was in course of preparation for the press, of seeing some remarkably fine electro-deposits of iridium, the hardest and most refractory and unalterable, of all the metals of the platinum group. These iridium deposits, upon various metals, exhibited a fine steel-gray lustre and color. The inventor, Dr. W. L. Dudley, of Cincinnati, stated to us that he had solved the problem of coating metals with iridium by the use of a suitable solution of the metal, and the proper regulation of the current, and that a company was engaged in practically working the process in Cincinnati.

To maintain uniformly the proper strength of the plating solution, a plate of iridium is employed as an anode. The metal, from samples which we had the opportunity of observing, is deposited in reguline form, and is susceptible of taking a good polish. A thin platinum sheet, electro-plated with iridium, retains its flexibility, and when

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