METALS. 205 



2. The separation of the mineralizing ingredients when 

 jhe ore is pure, is sometimes effected by heat alone ; thus the 

 common ores of mercury and lead, both sulphurets, will give 

 up the sulphur in part when heated. In most cases, some 

 material is added to combine with the mineralizing ingre- 

 dient and carry it off; as when certain iron ores (oxyds of 

 iron) are heated with charcoal, the charcoal takes the oxygen 

 (forming the gas carbonic acid which escapes) and leaves 

 the iron pure. 



3. When two or more metals are mixed in the ore, one i3 

 sometimes removed by oxydation, or in other words, it is 

 burnt out. Thus lead containing silver, is heated in a draft 

 of air ; the lead unites with the oxygen of the air and forms 

 an earthy slag, while the silver, which is not thus oxydated, 

 remains untouched. Such a process, carried on in a vessel 

 of bone-ashes, or some material of the kind, which will ab- 

 sorb the oxyd of lead formed, is called cupellation. (See 

 beyond under gold.) Much of the iron in the ordinary cop- 

 per ore (copper pyrites) is removed in the common process 

 of reduction in England by repeated fusions and stirring, 

 while exposed to a draft of air. 



4. When there are impurities present, or a mixture of the 

 gangue, which is commonly the case, a material is sought 

 for which will form, when heated, a fusible compound with 

 the gangue and impurities ; and this material is called &Jlux. 

 Most iron ores are associated with quartz or clay, quartz be- 

 ing pure silica, and clay containing 75 per cent, of silica. 

 Common limestone readily fuses into a glass with silica, 

 when used in the requisite proportions, and hence it is gen- 

 erally employed as a flux in iron furnaces. A salt of soda 

 or potash would produce the same result, for these are the 

 ingredients which form with silica common glass. The 

 glass formed is more or less frothy, and is called slag or scoria. 



Before reduction, the volatile impurities and any water 

 present, are often removed by a process called roasting. 



The processes of reducing the ordinary metallic ores in 

 the arts are combinations of the different steps here pointed 

 out. There are other chemical methods for certain cases, 

 which it is unnecessary to allude to in this place. 



How is the mineralizing ingredient separated in some cases ? How 

 in others 1 Explain by examples. How in cases of mixture. Ex 

 plain the process of cupellation. How in still other cases, and explain th 

 use of fluxes by an example. What is said in conclusion of the pro 

 cesses of reduction ? 



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