3756. To Prepare Iron for Coating with Copper

3756.    To Prepare Iron for Coating with Copper. When it is required to cover an iron article with copper, it is first steeped in hot caustic potash or soda, to remove any grease or oil. Being washed from that, it is placed for a short time in dilute sulpiraric acid, consisting of about 1 part of acid to 1G parts water, which removes any oxide that may exist. It is then washed in water, and scoured with sand till the surface is perfectly clean, and finally attached to the battery, and immersed in the cyanide solution. (See No. 3755 (Cyanide Solution of Copper).) All this must be done with dispatch, so as to prevent the iron combining with oxygen. An immersion of five minutes' duration in the cyanide solution is sufficient to deposit upon the iron a film of copper. But it is necessary to the complete protection of the iron, that it should have a tolerably thick coating; and, as the cyanide process is expensive, it is preferable, when the iron has received a film of copper by the cyanide solution, to take it out, wash it in water, and attach it to a single cell or weak battery, and put it into a solution of sulphate of copper. If there is any part not sufficiently covered with copper by the cyanide solution, the sulphate will make these parts of a dark color, which a touch of the finger will remove. "When such is the case, the article must be taken out, scoured, and put again into the cyanide solution till perfectly covered. A little practice will render this very easy. The sulphate solution, when used for covering iron, should be prepared by adding to it by degrees a little caustic soda, so long as the precipitate formed is redissolved. This neutralizes a great portion of the sulphuric acid, and thus the iron is not so readily acted upon.

3757. To Coat Iron with Zinc

3757.    To Coat Iron with Zinc. In covering iron with zinc, the precautions necessary for copper are not required; zinc being the positive metal, acids have a stronger affinity for it than for iron, and therefore an acid solution may bo used. The solution generally used is the sulphate, used in the same way as sulphate of copper. (See No. 3661 (Solution of Copper for Electro-typing).)

3758. Test for Galvanized Iron

3758. Test for Galvanized Iron.

When zinc is deposited on iron by galvanic agency, it should form a chemical combination with the iron, and not be merely attached thereto. It is proposed by Mr. T. Bruce Warren, of England, to use this fact for practically testing the efficiency of the galvanization. If mercury be poured over the surface, the zinc that is only locally attached will form an amalgam with the mercury. Mr. Warren also uses this as a quantitative test, to verify the amount of zinc in combination with the iron.

3759. To Make a Cyanide Solution of Brass

3759.     To Make a Cyanide Solution of Brass. Dissolve 1 pound (troy) cyanide of potassium, 2 ounces cyanide of copper, and 1 ounce cyanide of zinc, in 1 gallon rain or distilled water; then add 2 ounces muriate of ammonia. This solution is to be used at 160° Fahr. on smooth work, with a compound battery of 3 to 12 cells.