Page:The American Cyclopædia (1879) Volume XVI.djvu/847

 ZINC from the apparatus of reduction. The purest commercial zinc is that of Pennsylvania and New Jersey, as appears from the following analyses given by Kerl : FOREIGN SUBSTANCES. i. i!. 3. 4. 5. 6. 7. 8. 9. 10. Iron 0-24 0-186 0-101 0-155 0-15 0"041 Lead 0-3 to 2-0 2-898 1-563 1-100 0-45 0'27 to 0'91 0*503 0- i'i Cadmium traces traces 0-282 0-16 to 0-23 0-078 Nos. 1 and 2, Tipper Silesia; 3, Bleiberg; 4, Dombrowa ; 6, Carniola ; 6, Austria ; 7, La Salle, 111. ; 8, Bethlehem, Lehigh co., Pa. ; 9, Engis (from calamine) ; 10, Engis (from blende). The amount of arsenic in European zincs is said to range from 0'0005 per cent, in the best Belgian to 0'19 per cent, in the worst French. The zinc of Freiberg in Saxony contains about 0'04 per cent, of iridium ; that of Johannisthal in Carinthia, 0-2 to 0-5 per cent, of sulphide of lead ; that of New Jersey is doubtfully re- ported to contain traces of copper and tin. Manganese, antimony, and even cobalt and nickel, are also named as occurring in traces in commercial zinc. The Silesian metal de- rives its high percentage of iron (shown in the above table) from the kettles in which it is melted. Cadmium frequently accompanies it in its ores, as manganese does iron, replacing it to some extent in the chemical formulas of the minerals, or forming combinations isomor- phous with those of zinc. As will be inferred from the foregoing, zinc readily forms alloys, the most important of which are those with copper, or copper and nickel. Ordinary brass contains about VI '5 parts copper to 28-5 zinc; pinchbeck, 84'5 copper to 15'5 zinc. The term tombac, employed in German for pinchbeck, appears to be used at present by English wri- ters in a different sense. According to Brande, tombac is brass with an excess of zinc; and later English authors apply the term to white copper, an alloy of copper and arsenic. There are numerous other alloys of zinc and copper, or zinc, copper, and tin, composing 'a great variety of oroides or imitations of gold, bronze powders, button metals, &c. German silver or argentan (originally imported from China under the name of pacTcfong or white copper) is an alloy of copper, zinc, and nickel, much employed as a substitute for silver in utensils, and especially as a basis for the best silver plate (electro-plate). The general rule is said to be that copper and zinc in this alloy should bear the proportion of 8:3, and that the nickel should be not less than one fourth nor more than three fourths of the amount of cop- per. But Aubelen says that copper 3, zinc 1, and nickel 1 gives the best alloy for working, and also most nearly resembling silver ; and many analyses of good English ware approach this composition. The alloy of zinc and silver plays an important part in the processes of Parkes, CorduriS, Flach, and others, for the de- silverization of argentiferous lead. (See LEAD, and SILVER.) Apart from its alloys, zinc is used for ornamental castings (statuettes, &c.), which are to be painted, copper-plated, or bronzed. For this purpose it is adapted by its cheapness, fusibility, and property of filling the mould completely without shrinkage, giv- ing sharply defined castings. It is also em- ployed as sheet zinc in roofing, cornices, signs, vessels, &c. ; for coating iron (see GALVANIZED IRON) ; for sheathing ships ; as fuel, so to speak, in the galvanic battery ; and in the preparation of hydrogen by the decomposition of water. The Dobereiner lamp, once common, but now superseded by friction matches, is a small hy- drogen generator, consisting of a bell glass in which is suspended a piece of zinc, and which is placed in a jar containing very dilute sul- phuric acid. The action of the acid and water upon the zinc liberates hydrogen, which, col- lecting in the upper part of the bell glass, drives the liquid down and out into the sur- rounding jar ; so that when a certain quantity of the gas has accumulated the zinc is no longer in contact with the liquid, and the process ceases until, the hydrogen being drawn off, the liquid rises again under the bell, and again attacks the zinc. The hydrogen, when a light is required, is allowed to escape through a small cock at the top, and to impinge upon a ball of platinum sponge, which, condensing the gas in its pores, grows white hot, and sets the hydrogen jet on fire. For the production of pure hydrogen the zinc must be free from ar- senic, traces of which are common in the com- mercial article. This is particularly important in Marsh's test for arsenic. The most impor- tant compounds of zinc are the oxide, carbon- ate, chloride, sulphate, and acetate. The oxide, flores einci, ZnO (80 parts of zinc to 20 of oxygen), a soft white or faintly yellow, taste- less, and inodorous powder, turning lemon-yel- low when heated, and recovering its _ white- ness on cooling, has been used medicinally as a tonic and anti-spasmodic, in epilepsy, whooping cough, chorea, and various spasmo- dic affections, and as an exsiccant, externally applied in powder or in ointment to excoria- tions, slight ulcerations, &c. In the manu- facture of spelter and the melting of brass, a portion of the zinc is volatilized and oxidized, the exide settling on the walls of the furnace in a white or gray mass. The former is called by pharmacists nihil album, the latter tutia Alex- andrina, though under both these names sub- stances are now sometimes offered which consist of gypsum or other earthy minerals, without a trace of zincic oxide. The metallurgical name is furnace calamine or cadmia. The carbonate is best precipitated by pouring a hot, pure so- lution of the sulphate into one of sodic car- bonate. It is used medicinally in fine pow-