Every year adds to the general demand for electro-plated goods, and the experience necessary to produce them in the most perfect manner. The manufacture is based upon what has received the scientific name of electrolysis, that is, the decomposition of compound substances by means of the electric current. The current may be generated, either mechanically, with the ordinary friction machines, or chemically, as in the various galvanic batteries in use. The substance thus capable of being decomposed is called an electrolyte. Every electrolyte contains two or more elements which may be divided into two groups : those which are attracted to the positive pole of the battery, and those which go to the negative pole. These two groups are called ion, and those which move to the positive pole are called anions,-vf\\\Q those which move to the negative pole are called cations. To illustrate this, suppose the substance to be decomposed is sulphate of copper, in solution, and an electric current to be passed through it. Sulphate of copper is composed of copper and sulphuric acid, the latter of which is composed of sulphur and oxygen. Copper is a cation, hence it will move to the negative pole of the battery. Both sulphur and oxygen 154 are anions, lionce, tlie acid which the union of these substances forms will move to the positive pole without decomposition, as would be the case were either sulphur or oxygen a catTon. The terms im, anion, and cat'ion, were first suggested by Faraday. The first is derived from a Greek word, to go, and anion s'gnifies, literally, that which goes upward, while cation signifies that which goes down. These terms are applied to indicate the opposite directions in which substances move when their union is broken up by electrolysis, a word whch, literally, signifies to loosen by electricity. The laws which govern electrolysis are very simple. Bodies, with few exceptions, are only decomposed while in the liquid istate, brought about, either by fusion or solution. No elementary substance can, from the nature of the case, be an electrolyte. The direction of the electrolysis depends upon the arrangement of the battery and the amount of it is directly proportional to the quantity of electricity passed through the electrolyte. Those bodies, only, are electrolytes which are composed of a conductor and a non-conductor of electricity. The conductors of electricity accumulate on the negative pole of the battery, and are the cations. The non-conductors accumulate on the positive pole and are the anions. These comprise all the general laws of electrolysis, so far as known. The positive pole of a battery is now generally called the Kincodc, and the negative pole the platinode, because when zinc and platinum constitute the metallic plates of a battery, the zinc is positive and the platinum is negative. Electro-plating consists in the electrolysis of a metallic salt, the object to be plated being connected with the platinode of the battery, as the metals, being electro-positive elements, or cations, will move to that pole, and accumulate upon it. The objects to be plated must be chemically clean ; that is, they must be entirely free from dust, grease, oxide, or tarnish from any cause. Oxides and sulphides are conveniently removed by polishing with rouge, and grease may be removed by v/ashing with an alkaline solution. The surface thus pre pared, the article, having a small slip of metal slightly soldered to the back, it necessary for convenience in attaching the wire, is suspended on a hook so that it is immersed in the electrolyte, or solution of a metallic salt, and the negative pole of the battery being connected by a conducting wire with the article to be plated, while a wire from the positive pole is connected with the electrolyte,the decomposition of the salt, and the deposition of the metallic element contained in it at once commence. There are, however, many circumstances which may defeat success in electro-plating, and no amount of reading can compensate for practical experience in its execution. The metallic film may be imperfect, owing to the presence of impurities upon the surface of the article to be plated. This can be ascertained by examination, and remedied by the proper clean-ijig. Sometimes the rapid evolution of gas raises little blisters upo 1 the surface, and at others, the deposit, instead of being smooth and granular, will be rough and crystalline. A great variety ol means are employed by experts in the art to remedy these evils, such as wider separation of the poles, increasing the thickness of the conducting wire connected with the positive pole, warming the electrolyte, increasing or diminishing the number of elements in the battery employed, etc., etc. Experience, in these cases, is the best guide, in fact, it is the only one which can, with certainty, be relied upon. The article, having received a suflacient coating, is washed, dried, and burnished, with the exception of such parts as are desired to remain as deposited, and this completes the operation.
This article was originally published with the title "Electro-Plating and Gilding" in Scientific American 21, 10, 153-154 (September 1869)