The metals on which a coat of copper is deposited by electricity are lead and its alloys; tin and its alloys; iron, tinned iron; zinc; and steel. "When articles made of these metals are to be silver-plated, nickel-plated, or gilded, it is always advisable and sometimes necessary previously to coat them with copper. This cannot be done in a copper sulphate solution because that dissolves the metals. Various solutions have been used j but for the most successful one dissolve copper sulphate in hot rainwater. When cold, add strong liquid ammonia in small quantities and stir well with a stick each time. At first a green precipitate will be obtained; then, on adding more ammonia, the green precipitate will dissolve and form a clear azure-blue solution. To this add one of potassinm cyanide until the liquid assumes an amber tint, when rainwater should be added. The usual proportions are: Copper sulphate, loz.; potassinm cyanide, 3oz.; liquid ammonia, loz.; rainwater, 2 qt. Distilled water maybe used instead of rainwater, but spring and river waters are not suitable because of the earthy matters held by them. The solution should be held in an enamelled iron vessel.

If it is kept supplied with free cyanide and free ammonia it may be worked cold at from 6 to 8 volts; but the deposit may be improved by heating the solution to from 150° P. to 170° F., and the vat may then be worked at from 4 to 6 volts. The best generator is a plating dynamo, the next a three-cell accumulator; and among primary batteries the next best would be four A-gal. Bunsen cells. Anode plates of pure copper must be employed; these are connected by No. 16 S.W.G. copper wire to the positive pole of the generator. If the plates do not disssolved freely, but become encrusted with a green slime, a small quantity of potassinm cyanide and of liquid ammonia should be added to the solution. The surfaces of all articles to be copper-plated by this process must be cleaned and prepared. Iron and steel articles may tie cleaned from rust by steeping and swilling in a pickle composed of 6 fluid oz. of sulphuric acid and 1/2 oz. of muriatic acid in each gallon of water. They must then be rinsed in clean water and immersed in a pickle composed of 1/2 lb. of American potash dissolved in each gallon of hot water.

If the surfaces have been pitted, the corroded parts must be polished with emery held on a mop in a polishing lathe, after which the articles must be well swilled in the hot potash pickle to free them from oil and grease. All surfaces must be well polished before the copper is deposited, because the thin coat will not permit much polishing afterwards. Articles made of lead and tin, or their alloys, must be first scoured with sand and water, using a hard brush for the purpose, to free them from oxide; then rinsed in the hot potash pickle; again scoured with finer sand to polish them; wired with short lengths of No. 24 S.W.G. soft copper wire; again rinsed in the hot potash pickle, and transferred direct to the plating vat. The potash pickle will prevent rust forming on iron and steel articles, and will clear oxide from lead and tin and their alloys; but it is advisable to transfer the articles quickly to the plating vat, and not to rinse them in water on the way. Zinc articles are cleansed in a similar manner; but very fine sand or finely powdered bath brick must be used in scouring. If articles are bright and free from rust or tarnish, only a light brushing with a vegetable fibre brush in the potash pickle will be necessary to prepare them.

Each article must be attached to a short length of copper wire, which suspends it in the vat. Use No. 24 S.W.G. for small articles, and No. 18 S.W.G. for heavy ones. Each article should be held by the slinging wire during the final rinse, and the free end of this wire is bent over a brass rod on the plating vat, attached to the negative pole of the generator. Move each article to and fro with a rinsing movement when placing it in the vat, to remove any air bubbles on the surface. The current should be regulated by a resistance, usually a long length of German silver wire furnished with a switch. The resistance can also be increased by diminishing the surface of the anode exposed to the plating solution, and by placing the anode further from the article being plated. If the current is too strong, the deposited copper will be dark in colour and loose in character, and this will also happen if the solution contains too much copper. Movement of the articles whilst being plated will assist in securing a bright and smooth deposit.

Some gas is given off from the articles whilst deposition is going on, but this should be regulated by adjusting the current. Only a few minutes is required for plating each article. The plated articles should be rinsed in plenty of clean water to free them from cyanide and copper salts. If the surface is to remain coppery, the i'- should be rinsed in hot water, placed at once in hot bran or hot sawdust, and moved about therein until quite dry and bright. Pure copper rea lily tarnishes in the air when damp, but may be brightened with a scratch-brush. If the surface is to be nickel-plated the articles must be rinsed and transferred at once to the nickel-plating vat. If a thicker deposit of copper is desired, use an electrotyping solution, after depositing a thin film of copper in the alkaline solution above mentioned. If the plated articles are to be gilded, get a very thin and bright deposit of copper, or brighten it with a scratch-brush; then rinse and transfer at once to the gilding vat. If they are to be silver-plated, coat with a thin film of mercury before placing them in the silver-plating solution.

The solution is made by dissolving 1oz. of mercury in very dilute nitric acid, say 1 part acid to 10 parts distilled water, then making it up to 1 gal. of solution with distilled water. Give a brisk swill in this, and then rinse in clean water.