Or dissolve ounce of gold in 1 ounce of aqua regia, or a mixture of nitric and muriatic acids. Add 1 quart of soft water, and throw in gradually hyposulphite of soda in crystals. A brown sediment will form which will again dissolve if ad ditional hyposulphite is added. When this has dissolved, add a little more hyposulphite and immerse small ar ticles, or apply the solution by means of a brush or sponge.
Or use this solution to touch up gilded articles where the gilding has worn or been taken off by accident. Apply by means of a brush, and at the moment touch the spot with the bright side of a piece of shaving whittled from a piece of zinc.
The above are suitable for silver, copper, or brass.
Solutions for German-silver Pla ting.—To make a solution for elec troplating German silver and other metals, take the plate of German silver of a known composition and prepare a mixture of chlorides of the metals in the same proportion that they are found in the alloy. If, for example, the German silver consists of 1 part nickel, 1 part zinc, and 2 parts copper, dissolve 1 ounce of nickel, 1 ounce of zinc, and 2 ounces of copper in hydrochloric acid, and evaporate the excess of acid by gen tle heat. Dissolve this solution in the water for the bath, and add slowly potassium cyanide. The metals will be first precipitated, but as the cy anide solution is gradually added and the bath stirred, the metals will be redissolved. The solution will then be ready to apply, but to obtain the best results it should be raised to a temperature of at least 60°. The plate of German silver is suspended from the positive pole, and the arti cle to be plated, suitably cleaned, from the negative pole.
Brass Plating.—Prepare separate solutions of cyanide of potassium and neutral tartrate of ammonia in water, mix the two solutions for the bath, and add the cyanide of copper and zinc in the proportions desired for the alloy until the bath is satu rated, or until they commence to pre cipitate. Then add black oxide of copper and pure zinc white until the bath has dissolved all it can. This admits of the use of a weak galvanic current. If the color of the brass is too light, a little more copper salt may be added, or if too dark, a little more zinc salt. A brass plate of the composition desired is connected with the positive pole of the battery, and the zinc or other metal to be coated, with the negative pole. The latter must, of course, be thoroughly cleaned with acids and by scrubbing to give a chemically clean surface for the deposit.
Hints for Electroplating. — The process of electroplating with single metals, as copper, silver, gold, and the like, on various solid metals is very simple, but electroplating with alloys, as German silver, brass, and the like, is somewhat more difficult on account of the fact that the elec tric current shows a tendency, if the bath is not properly prepared, to de posit one of the metals contained in the alloy in preference to the others; hence some little experimenting will be required to succeed in electropla ting with alloys.
A weak current gives the best re sults with single metals, but with al loys it tends to favor one of the metals at the expense of the others. A strong current tends to deposit a rough, thick film which is not tena cious and does not adhere well to the article; hence care should be taken to prepare the solution for alloys exactly according to instruc tion.
The cyanide solution, which is al ways used for the precious metals, will give better results with alloys than the sulphate solution used in copperplating. All objects to be elec troplated must be carefully cleaned before they are put in the bath; hence they should be dipped in the mix ture of nitric and muriatic acids to remove any oxides, rinsed in water, and, if necessary, scoured with pure water and sand. On removal from the bath after plating, they may be dried in sawdust, cleaned, and polished.
Electroplating Silver on Iron.—To plate iron or steel, dissolve cyanide of potassium in soft water, using I pound of the cyanide to 1 quart of water. Dip the articles in pure sul phuric acid, scrub with fine sand and a scouring brush, rinse with pure water, and suspend them in the cy anide solution until it becomes white. Remove and suspend in the silver so lution.
Or first coat the steel or iron with sulphate of copper by suspending it in a bath of sulphate of copper, and deposit the silver solution on this coating.
To Plate Iron without Electricity. —To plate iron with silver without electricity, clean and smooth the sur face with a burnisher, heat it to blue ness, lay the silver leaf upon it and burnish it down. Continue adding silver leaf until the proper thickness is secured.
Or apply soldering liquid to the iron, and thin sheets of solder. Lay the silver over this, and heat gently until the solder melts.
Or tin the iron. First lay tin foil over it, and silver leaf or thin sheets of silver over all, and melt the tin with gentle heat.
Solution for Nickel Plating.—A pure solution of the double sulphate of nickel and ammonia gives a thick deposit with Et smooth surface capa ble of taking a high polish, but this solution must be chemically pure and free from foreign ingredients, espe cially nitric acid, alkalies, and lime. If these are used to clean articles to be nickel plated, the utmost care must be used in rinsing them, as a drop of nitric acid will ruin the solution by causing the nickel plate to become black and streaked. Potash or soda gives tt deposit of green oxide of nickel. Other metals, as copper, zinc, and arsenic, must also be avoided. Instead of a pure nickel plate at the positive pole of the battery, better results are obtained by a plate com posed of nickel combined with car bon, and such casting nickel plates are now obtainable on the market.