The smelting for which the calcination, roasting, crushing, etc., are preliminary prepara tions processes; consists in separating the metal and gangue by their difference in specific gravities after fusion. A necessary adjunct of the smelting operation is a flux which renders the naturally infusible gangue readily fusible by the formation of a slag with it which is easily separated from the heavy metal. The fluxes are earthy materials and may be acid or basic, depending on the character of the ore used. Acid gangue in the ore requires basic flux and vice versa. Lime, a basic flux, is usually used in the carbonate form or limestone. Fluorspar, calcium fluoride, is used only in small amounts to increase the fluidity of the slag. Barytes, strongly basic, also reacts as a desulphurizing agent. Silicious or acid fluxes are sand, quartz, etc. Smelting is usually either oxidizing or reducing. The reducing smelting in treating oxide ores has for a reduc ing agent carbon monoxide formed from coke which is a part of the furnace charge. Oxidiz ing smelting is practised mainly with the pur pose of refining a crude metal as many metallic impurities can be removed in this way. Other metallurgical processes are liquation, where advantage is taken of the difference of melting points of easily fusible compounds from infus ible ones, when the combination is heated to the lower melting point the more easily fusible runs out leaving the highly infusible gangue; distillation and sublimation, where the metal is driven off as a vapor, then condensed as a liquid or solid; scarification, or the roasting of an alloy with the object of removing the more oxidizable metal as a slag. This process is used practically only for separation of silver and lead. Other processes are cupellation, similar to scarification where the oxidizing is carried out on a hearth or oval which is of a material to absorb the fused oxide.
Wet Metallurgy in general involves the separation of a metal in the form of a solahlt salt from the insoluble gangue by means of ; solvent followed by the recovery of the dis solved substance, by evaporation or precipil tion. Amalgamation is a process in which thf ore, usually gold or silver, is treated with me- cury which dissolves the metal, and on setst quent heating the mercury distilled off, leatinz the metal. The ores need to be in a divided state and in such form as to be amenable to solvents which frequently mean: preliminary treatment, as roasting, weatheri•.:
etc. The solvents in common use are war aqueous solutions of gases; acids; bases, sz;; solutions. These solvents are used diluted are warmed. Ores for leeching are classed k sands and slimes, the sands being coarse atott6• to permit the leeching by percolation. Me slimes are so fine as to prohibit this method an require an agitation of slime with solvent This gives a colloidal solution which must coagulated, then separated by filtration decantation. The solution is then conceniratr. by evaporation and the salt crystallized o-,:t In dealing with precipitates they are usuaii dried in muffle, or reverbatory furnaces. Tr.r modern and most efficient method of trearir.: slimes is by the flotation process of separati7: The slime or pulp is fed into the bottom of tank and agitated with oil and compressed air Under this treatment the metal particles tio2 on the surface while the gangue particles sick Metals produced by the above methods ,a:t rather impure. For final refinement of a me and its production in the purest possible electrolysis is resorted to. Reduced to its plest form electrolysis consists of a solution a salt of the metal to he purified in which h, electrodes are dipped, one being of the imptrf metal and the other of the pure. When electric current is passed through this bath electrode of impure metal is dissolved aw-.1 and chemically pure metal is deposited on other electrode. After the metal is by some of the above processes it is usir.'1 made into some alloy by fusion with cd•r• metals and elements, then cast from the meItc state into the finished shape or into inew which must be forged by hammering, rollir pressing, etc., into the desired form. hot working operations are frequently foilcmt' by cold rolling as strips, sheets, spinning cr pressing for shapes, cold drawing for wire. these operations require careful and freqty-.t heating and cooling. The metal must be nealed to remove strains and make it soft ! the case of steel produced by alloying cal-IN- and iron it may be used for tools which re quire hardening and tempering by heating to 2 definite temperature, quenching in water or clit then reheating to some lower temperature.
All of these processes fall under the nietil lurgist's care as surely as the original extrv don and refining. Sec ALUMINUM; ODeers: