To charge this battery, add five fluid ounces of sulphuric acid to three pints of cold water, pouring the acid slowly into the water and stirring it at the same time with a glass or carbon rod. When this becomes cold, after standing a few hours, add six ounces of finely pulverized bichromate of potash. Mix this thoroughly, and pour some of the solution into the glass cell until it is three-fourths full; then it will be ready to receive the carbons and zinc. When arranging the wood-clamps on the carbon and zinc plates it would be well to make two of the clamps longer than the others so that they will extend out far enough to rest on the top edge of the jar. To keep them in position at the middle of the jar, notches should be cut at the underside of these clamps, so that they will fit down over the edge of the jar. Any number of these cells may be connected together to obtain the desired amount of current, or electro-motive force. Other batteries suitable for electro-plating are the Edison primary, Taylor, Fuller, Daniell, gravity, Groves, and Merdingers. All of these may be purchased at large electrical equipment or supply houses. The Cleansing Process One of the most important operations of the plating process is to properly cleanse the articles to be plated before they are placed in the bath. When once cleaned the surfaces of these objects must not be touched with the fingers, or any dusty or greasy object; otherwise the electro-deposited metal will not hold on the surface, but will peel off, in time, or blister. A very small trace of foreign matter is sufficient to prevent the deposit from adhering to the surface to be plated; therefore, great care must be taken to eliminate all trace of anything that would interfere with the perfect transmission of metallic molecules to the prepared surfaces. Acids are chiefly employed to remove foreign matter from new metallic surfaces; and for copper, brass, iron, zinc, gold, and silver a table is given on page 281 which will show the right proportion of acids to water in order to cleanse the various metals. In the following scale the numerals stand for parts. For example: the first one means 100 parts water, 50 parts nitric acid, 100 parts sulphuric acid, and 2 parts hydrochloric acid--making in all 252 parts. These can be measured in a glass graduate. ----------------+-----+------+---------+------------ | |Nitric|Sulphuric|Hydrochloric |Water| Acid | Acid | Acid ----------------+-----+------+---------+------------ Copper and brass| 100 | 50 | 100 | 2 Gold | 100 | ... | ... | 15 Silver | 100 | 10 | ... | ... Wrought-iron | 100 | 2 | 8 | 2 Cast-iron | 100 | 3 | 12 | 3 Zinc | 100 | ... | 10 | ... ----------------+-----+------+---------+------------