Page:The New International Encyclopædia 1st ed. v. 09.djvu/22

GOLD. GOLD-BEATING. tailings to float away. At intervals the amalgam on the boxes and on the plates is removed and is placed in retorts to which heat is applied, vapor- izing the mercury and leaving the gold as metal. Extraction by Aqieois Solution. There are two principal methods of extracting gold . by means of aqueous solutions, known as the Platt- ner or chlorination process and the MacArllmr- Forrest or cyanide process. The chlorine process consists first in calcining the ore in furnaces, by which all the metals present except gold and silver are converted into oxides, which are not acted upon by chlorine. The next process is the application of chlorine gas to the calcined ores in chlorination vessels. The result is the forma- tion of auric cliloride or chloride of gold, which is leached out of the ore by means of water. To this aqueous solution of auric chloride sulphate of iron or cliarcoal is added, which precipitates the gold. This precipitate is finally treated to remove impurities. In the cyanide process the crushed ore is treated with a solution of potassio cyanide, the addition of zinc to which will pre- cipitate the gold. The process has been most suc- cessfully practiced in the Transvaal in treating the tailings from the amalgamation process. Parting. As the greater part of the gold pro- duced by the preceding processes carries silver (see Silver), the parting of the gold from the silver is an important process in the metallurgy of gold. Parting is performed in what are known as the dry w-ay and the w?t way, and by electroly- sis. The dry method of parting depends upon the fact that silver can be converted into sulphide or chloride, while gold is attacked by neither sul- phur nor chlorine at high temperature. The wet method depends upon the solubility of silver and the insolubility of gold in nitric acid, and in boiling concentrated sulphuric acid. The elec- trolytic method depends upon the property of silver to pass from a bar of gold-silver alloy employed as an anode to the cathode when the two poles are immersed in an acidulated solu- tion of nitrate of silver, and an electric current established. The wet process, using sulphuric acid as the solvent, and the electrolytic process are the two parting processes most employed at present. For a full treatment of the inetallurg^' of gold, consult : Schnabel, Hatidhook of Metal- lurgy, translated (New York. 1880) ; Egleston, The Mcfalliirfjy of ftilrer. flold, and Mercury in the United States (New York. 1887). Commercial Uses. It is estimated by compe- tent authorities that about one-fourth of the annual production of gold is employed in coinage, the remainder being consumed in the arts and in making good the annual loss from various causes. The purposes for which gold is employed in the arts are familiar to every one. Some of the items are jewelry plate, gold leaf, gilding, etc. Bibliography. Suess, Die Ziikunft dex Goldes (Vienna. 1877) ; Delmar, History of the Precious Metals (London, 1880) ; Lo<'k. Gold. lis Occur- rence and Extraction (I.«ndon, 1882) ; Patterson, New Golden Afje. and Influence of the Precious Metals on the World (London. 1882) ; Soetbeer. Materialien zur ErWuterung und Beurteilung der wirtschaft lichen Edehnetalh-erhaltnisse (Ber- lin, 1886) ; Weil, L'or {chiinie. geologic, mine- ralogie. metallurgie) (Paris, 1895) : Hatch, The Gold Mines of the Rand (London, 1895) ; Rose, Metallurgy of Gold (London, 1896); Eissler, Metallurgy of Gold (London, 1896) ; Kemp, Ore Deposits of the United States (New York, 1900) ; The Mineral Industry (Kew York, 1893 et seq. ) . Statistics may be found in the Annual Reports of the Director of the Mint (Washington, 1880 et seq. ) . GOLDATJ, gdl'dou. A village in the Canton of Schwyz, Switzerland ( Map : Switzerland, C 1). It was formerly situated between Mount Rigi and the Rossberg, and was the scene of the terrible landslide from the Rossberg, September 2, 1806, which destroyed Goldau and three other villages, burying 457 people, and filling up part of Lauwerz Lake. The present village of Goldau, built near the mines, contained a popu- lation of about 500 in 1000. GOLD-BEATER'S SKIN. A delicate mem- brane prepared from the large intestine of the oz, and used as the fabric for court-plaster, etc., but chiefly by gold-beaters. The outer or peritoneal membrane is used for this purpose. The intestine is first subjected to a partial putrefaction, by which the adhesion of the merabranes is suffi- ciently diminished to enable them to be sepa- rated; the separated membrane is then further cleaned from adhering muscular fibres, dried, beaten, and pressed between paper, besides being treated with alum, isinglass, and white of egg, the object of which is to obtain the pure con- tinuous membrane free from grease and impuri- ties, and thus prevent weakening by putrefactive processes. When thus prepared, gold-beater's skin may be beaten continuously for several months with a twelve-pound hammer without material injur}'. The intestines of 500 oxen are required^ to furnish the 900 leaves that form one packet, or mold, as it is technically called. The manufac- ture is extremely oft'ensive. Clilorine has been introduced both as a disinfectant and to assist in the separation of the membrane. GOLD-BEATING. The process by which gold is hammered into thin leaves. The use of gold leaf for gilding is a very ancient art. having been practiced by the Egyptians and Greeks many centuries before the Christian Era, and gold used for this purpose is usually alloyed with silver or copper, according to the color re- quired. The consumption of gold leaf by dentists is also general, as the material in this form is extensively used for fillings. As gold leaf is not sold by weight, but by superficial measure, and as increasing the quantity of alloy diminishe3 the malleability, there is but little temptation to use the baser metals as an adulteration. The gold is first cast into oblong ingots about three- fourths of an inch wide, and weighing two ounces. The ingot is flattened out into a ribbon of about ^^ of an inch in thickness by passing it be- tween polished steel rollers. This is annealed or softened by heat, and then cut into pieces one inch square: 150 of these are placed between leaves of vellum or tough paper, each piece of gold in the centre of a square leaf, another placed above, and so on till the pile of 150 is formed. This pile, called a cutch, is inclosed in a double parchment case, placed upon a marble block, and beaten with a 16-pound hammer. The elasticity of the packet consideralily lightens the labor of beating, by causing the hammer to rebound with each blow. The beating is continued until the inch pieces are spread out to four-inch squares; they are then taken out and cut into four pieces. The