Page:Popular Science Monthly Volume 91.djvu/653

 Popular Science Monthly

��Make up another solution- of I oz. of the cyanide salts in a quart of pure water and pour enough of this over the washed precipitate to dissolve it, stirring well. When a clear, colorless liquid results, add more of the cyanide solution as there must be a slight excess of cyanide in the plating bath. Add enough water to give the desired quantity or strength.

If pure silver nitrate can be obtained, it may be used instead of the metal solution. Pure nitrate will contain approximately 635 grains of the metal in each 1000 grains of the salt.

A very good solution for ordinary work can be made by dissolving 1 oz. of pure' silver nitrate in 40 oz. of water and pro- ceeding as above to throw down and wash the precipitate and redissolve it in the cyanides. By adding two quarts of water, it is ready for use.

Preparing the Article to Be Plated

Having prepared the apparatus and solutions, the preparation of the work to be plated is next in order. Plating will cover no defects, such as stains, scratches, etc., but is likely to make them more prominent. Every blemish should be re- moved with a file or emery paper and the surface polished.

To remove corrosion from brass, copper, etc., soak the article in a. solution made by adding — a little at a time with free stirring 1 — 3 oz. of sulphuric acid to 4 oz. of water, and when this has cooled, pour in 1^ oz. of nitric acid. Be sure to add the sulphuric acid to the water a little at a time, allowing it to mix and cool before adding more, finally adding the nitric acid. Soak the work to be cleaned in this solution until all the corrosion is dissolved, or softened so that it may be removed with a stiff brush; then rinse thoroughly and polish. The time required to remove corrosion will vary from a few seconds to an hour or more.

Those parts which are to have a polished appearance when finished must be well polished before they are plated. This may be done in any way convenient. To use a polishing lathe or stand is the best method. Cloth disks, from 3 in. to 6 in. in diameter and l /2 in. to 1 in. thick may be made, some of canvas or other heavy, hard cloth, and others of flannel or muslin for the finishing touches. They should be used with powdered abrasives, using emery for the rougher operations and finishing with fine polishing powders and soft disks. If a

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lathe is not at hand, use brushes, and cloths.

When the work has been polished it should be washed thoroughly so that no traces of the polishing materials re- main. After polishing and washing, the articles should be attached to the slinging wires so that they need not be touched by the hands again. Soak the work a few moments in a hot solution made of a table- spoonful of potash in a pint of water. This is the potash "dip" and is to remove all traces of grease and dirt that may have been left.

After being given the potash dip the work is laid on a board where a small stream of water may flow over it while it is brushed with a stiff bristle brush, kept wet and occasionally dipped into pow- dered pumice stone. This will remove all the potash and grease and also give a slight grain to the surface of the plated article.

After scouring, rinse the work well in running water and soak for a few seconds in a solution made by dissolving an ounce of potassium cyanide in a pint of water and hang at once in the plating bath. Have the anode in position and the battery connected before hanging the work; other- wise the cyanide in the bath will attack the metal and injure the bath. The article will become white in a moment and a plate of silver will be deposited in from ten to fifteen minutes.

The Finishing Touches

When plated heavily enough, the article should be taken from the bath, rinsed in boiling water and dropped into fine, warm sawdust to dry. Exposure of a freshly plated surface to the air and light while it is covered with a film of the plating solu- tion, will cause it to turn yellow. When dried in the sawdust, it should be brushed and will appear a frosty white.

The first finishing is scratch brushing. A small brush wheel of fine brass wire is held in a lathe or polishing stand, and kept wet with stale beer or oatmeal water. The plated surface is held against it. Without a machine a bristle brush may be used, if stiff enough. When all the chalky whiteness has disappeared and the metal shows an even, dull color, give it another rinsing in plenty of water and dry. It is now ready for buffing and polishing with soft materials, light pressure and fine polishing powders.

If an extra heavy and durable plate

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