Page:The American Cyclopædia (1879) Volume XI.djvu/433

 METALLOIDS for oxygen is the basis of a classification for- merly much used. It is embodied in part in the electro-chemical series of Berzelius, which played an important part in the development of chemical science. The alkaline metals oxi- dize rapidly in the air, and decompose water at ordinary temperatures ; others, as iron and zinc, do not oxidize in pure dry air, and de- compose water only at a red heat, or in con- tact with an acid; and others, as the noble metals, do not decompose water at any tem- perature. The electrical relations of the metals correspond in general to their affinity for oxy- gen. Thus, the alkaline metals are the most electro-positive, and the noble metals the most electro-negative. The metals likewise fall into groups in which the individual members can replace one another in compounds without change of crystalline form ; they are then said to be isomorphous. As examples may be cited mag- nesium, calcium, manganese, iron, zinc, copper, and aluminum; barium, strontium, and lead; sodium, silver, thallium, gold, and potassium; arsenic, antimony, and bismuth ; tin, titanium, tungsten, and molybdenum ; platinum, iridium, and osmium. The atomicity of the elements, or their combining values, forms the basis of classification for study in modern chemistry. Metals are thus divided into monads (or those replaceable by or equivalent to one atom of a monogenic element, as hydrogen or chlorine), dyads, triads, tetrads, pentads, and hexads, as follows: monads lithium, sodium, potas- sium, rubidium, calcium, silver; dyads cal- cium, strontium, barium, glucinum, yttrium, lanthanum, didymium, erbium, thorium, mag- nesium, zinc, cadmium, copper, mercury; triads gold, thallium ; tetrads titanium, tin, aluminum, zirconium, rhodium, ruthenium, palladium, platinum, iridium, osmium, lead, manganese, iron, cobalt, nickel, cerium, indium, uranium; pentads vanadium, arsenic, anti- mony, bismuth, niobium, tantalum; hexads chromium, molybdenum, tungsten. A few of the metals possess more than one atomicity, and appear in different compounds with differ- ent atomic values. The combinations of the metals with the non-metallic elements may be divided into two classes, those with chlorine, iodine, bromine, and fluorine, and those with oxygen, sulphur, selenium, and tellurium. The former class are saline compounds, while the latter are generally basic, exceptionally acid, as before mentioned. Formerly the distinction was generally observed between haloid and oxygen salts, the former being the combination of a metal with a haloid body, as chloride of sodium, and the latter a combination of a basic oxide with an oxy-acid, as sulphate of soda. In the modern chemistry both characters of salts are regarded as the replacements of hydrogen in the acid by a metal. The combinations of the metals among themselves are known as alloys, or, in case of mercury, as amalgams. (See ALLOY, and AMALGAM.) METALLOIDS. See METALS. METALLURGY 421 METALLURGY (Gr. //eraAAovpyd?, working met- als), the science which treats primarily of the separation and isolation of the metals contained in their natural combinations or associations, known as ores, and secondarily of the manipu- lation of the metals and the production of metallic compounds or alloys. The modes of occurrence of metals in nature are: 1, native, either pure or alloyed ; 2, sulphides and com- binations of sulphides and arsenides ; 3, oxides and combinations of oxides with silicic and carbonic acids. More rarely arsenides, chlo- rides, tellurides, &c., are met with, and also compounds of oxides with other acids than those mentioned, as phosphoric, sulphuric, &c. The metallurgical treatment of an ore depends first on the physical characters of the minerals and accompanying rocks, and secondly on their chemical composition. It may therefore be divided into mechanical and chemical, the former dealing with the sepa- ration of native metals or metallic combina- tions from enclosing rock and gangue, and with the separation of associated minerals from each other according to their relative specific gravities ; and the latter with the reso- lution of the chemical combinations of the met- als with the non-metallic elements and with each other. The separation of the associated minerals and of minerals and metals from the gangue is usually effected by purely mechanical contrivances known as ore-dressing and ore- concentrating machines. Sometimes the metal or mineral is isolated by a process of liquation, heat being used (bismuth, sulphide of anti- mony). I. ORE DRESSING. The dressing of ores is the separation by mechanical means, prelim- inary to further treatment, of the worthless portions of the material obtained in mining. This art is usually referred to the province of the mining engineer, rather than the metal- lurgist, because in most cases, where the mines and reduction works belong to separate propri- etors, the former are expected to deliver ores to the latter in a suitable condition for treat- ment. But strictly speaking ore dressing is a metallurgical process. Gillon classifies it a8 "mechanical metallurgy." Every ore has a valuable and a worthless portion, and there may be also an injurious portion, which causes loss in the treatment. To remove the worth- less portion (gangue) and the actively inju- rious portion, by mechanical means, is the object of ore dressing. In a few instances, such as the washing of coal and the simple panning or sluicing of gold without amalgama- tion, the separation furnishes, without further treatment, the marketable commodity desired. But these operations, though involving the same principles, are not usually classed as ore dressing ; and in most instances the mechanical preparation merely precedes the actual process of reduction. Whether any given ore should be subjected to this preliminary treatment is a question of economy, involving local condi- tions of expense and the unavoidable loss of