almost without regard to temperature, and its simple formula should render it preferable to all others, were it not that it is variable in its operation. This bath, he adds, is especially open to the objection of ungilding one face of the object while the other face is being gilded, or of producing a red gilding at the bottom and a yellow one at the top of an object. This inconvenience, and others not enumerated, he concludes, may be made to disappear, though only imperfectly, by a prolonged ebullition. The first formula alone is recommended by this authority for the direct gilding of wrought iron, polished cast iron, and steel. The gilding obtained upon these metals with the other formulæ above named he does not consider to be so good. For gilding polished steel without the interposition of copper, Roseleur recommends the operator to diminish by one-half the proportion of cyanide indicated in the first formula; his proportions would therefore be of cyanide to 1 of gold. part The articles of steel, after cleansing by alkalies, are rapidly passed through a very diluted solution of hydrochloric acid, wiped off when practicable, and immersed in a very hot bath with an intense galvanic current at the beginning, which is gradually diminished afterwards by progressively withdrawing the platinum anode. Small articles of steel, such as pens, watch-hands, etc., are threaded upon a thin brass wire, and separated one from the other by glass beads. After cleansing, they are suspended in a boiling bath, then rinsed, and dried in hot and dry sawdust. Steel that has been tempered blue, is at once discolored by its passage through very dilute hydrochloric acid (say ' acid). The practice of the William Rogers Manufacturing Company, of Hartford, Conn., is to deposit gold and silver direct on iron and steel. In the gilding of Britannia metal, German-silver, etc., as the practice of this establishment is to use the gilding solution hot, these compositions are first coppered or silvered in a cold bath in the usual way, as the hot alkaline solution would oxidize these metals and the gilding would be without adherence. The proportions of the double cyanide gilding bath, as above remarked, are varied very much in practice without affecting the quality of the work, as will appear from the following statements derived from various authoritative Gore (Electro-Metallurgy, 131) recommends as sources. The same author states that the proportion of gold in the electro-gilding solutions used in large establishments, varies as much as from ounce to 50 Troy ounces to the gallon. We may add that the gilding solution used by the Wm. Rogers Manufacturing Company, of Hartford, contains considerably less than ounce gold to the gallon. Napier (Electro-Metallurgy (1876), p. 168) recommends for general work a gilding solution containing from onehalf to one ounce of gold, but adds that for gilding small articles, "a weaker solution will do." Urquhart (Electro-Pluting, 174) on this point has the following: "The proportions of gold and potassium cyanide to the gallon of solution vary according to the class or kind of work to be done in it. A fourth of an ounce of gold will be found to work; half an ounce will afford a better deposit in less time; and one ounce is sufficient for all ordinary work. The current needed for the richer solutions is small. Rich solutions admit of the complete art of electro-gilding being practised, and the various shades of color being given to the articles; while the weak solutions are only fitted for practically one color of gilding." Watt (Electro-Metallurgy, 59) remarks that "some gilders use five or six pennyweights of gold to the quart of solution, others as much as eight or ten pennyweights; but I have generally found that a solution containing less gold will give better results than one richer in metal, independent of the advantage in point of economy. I have observed that a bath containing five or six pennyweights of gold to the quart of water, and the necessary proportion of cyanide, and worked in several united cells of Smee's battery, has required a much larger surface of anode to be exposed to a given surface of negative electrode (that is, the article to be gilt), than would be required to gild an article in a solution containing one and a half pennyweights to the quart of solution, worked with a single cell of constant battery. Hence I infer that the weaker solution is the better conductor of the two." Napier (Electro-Metallurgy, 168) calls attention to the fact that the temperature at which the bath is worked has a decided influence on the color of the deposited gold, as well as on the current required. The hotter the solution the less current is required. "Generally," he adds, "three or four pairs of plates are used for gilding, and the solution is kept at 130° to 150° Fahr.; but one pair will answer if the solution is heated to 200° Fahr. For gilding German-silver, Watt prefers to work the bath at a lower temperature than usual with hot baths, to weaken the solution, and to expose a smaller surface of anode. The bath, he directs, should be so weak that the German-silver will not deposit the gold per se (that is without the battery); for gilding iron and steel goods, he directs that the bath should be weaker than for any other metal; and for this purpose, recommends the following, with which Gore substantially agrees: Watt's Formula for Gilding Iron and Steel. 4 parts. 16 66 20 66 This solution would contain between 3 and 4 dwts. of gold to the gallon. It should not be worked so hot as the ordinary solution, and with weak current, and small anode surface, and deposition must take place at first very slowly. He prefers also to give articles of iron or steel a preliminary coat of copper or brass before gilding. Gore, on the other hand, in his directions as to gilding, conforms very nearly to the usual American practice, in omitting the preparatory coppering of iron and steel. Respecting other base metals, he recommends (ElectroMetallurgy, 142) before gilding that articles composed of antimony, lead, tin or zinc, Britannia-metal, pewter, type metal, etc., should receive a film of copper or brass in a cyanide solution. In this connection, it may be observed that all authorities on this subject, with the single exception of Roseleur, agree in the statement that no solution has been found to work so well for electro-gilding as the simple cyanide of gold, dissolved in a solution of cyanide of potassium, or the double cyanide of gold and potassium dissolved in water. It is possible that the inconveniences attendant upon its use, as reported by Roseleur, may be due to the method of preparing it. For it will be observed, Roseleur, in this and several other formulæ recommended by him, adds the chloride of gold directly to the potassium cyanide solution, without first converting the gold into cyanide. The additional labor required to do this is very slight, but many electro-gilders follow the same careless method. The result is that there is formed in the gilding bath a quantity of chloride of potassium which is the equivalent of the gold chloride decomposed by the cyanide; and careful observers, who have studied this subject, do not hesitate to affirm that the presence of this foreign salt often seriously interferes with the successful working of the bath, when everything else may be in perfect order. It is worthy of notice also, that Roseleur in his directions for preparing the usual cyanide bath for electro-plating (silvering) calls attention to the practice followed by some operators of adding their chloride or nitrate of silver directly to the cyanide, and deprecates the practice as objectionable on the same grounds that we base our objection to his analogous mode of preparing the electro-gilding bath. It is certainly safer, and will be found more satisfactory by the operator, to first convert the chloride of gold into cyanide by the gradual addition, drop by drop, of cyanide of potassium, with constant stirring, and allowing the precipitate |