III. METALLURGY. 



Metallurgy embraces those chemical processes by which 

 metals are extracted from their ores, as well as those bj 

 which the crude metal is refined or purified, and may be ex- 

 tended to embrace further operations which have in view the 

 production of alloys, or other modifications, which still present 

 the metallic character. The extension of chemical technology 

 has evolved new processes for extracting metals from their 

 ores, and for producing metallic surfaces and other effects, 

 without the employment of fire, which was an element in for- 

 mer metallurgic processes. These processes being chiefly due 

 to the employment of chemical agents, or the metals them- 

 selves in aqueous solution, a distinct branch of metallurgy has 

 arisen, which we term hydrometallurgy, in distinction from 

 the more ancient pyrometallurgy. We have thrown the metals 

 into groups, dependent on their similar mode of occurrence 

 or similar treatment, beginning with iron, which is the most 

 important, and which is exclusively obtained by the reduction 

 of its oxide. Fuel affords heat for breaking up chemical af- 

 finities already existing in the native compounds of the ores, 

 and is at the same time the reducing agent for oxides. As 

 ores are never found in a pure state, but always accompanied 

 by foreign mjitter, this matter is removed by the addition of a 

 flux, which fuses with the foreign matter to a glass or slag 

 (cinder), and is then removed from the metal. 



On ancient metallurgy and mining in Britain, see an article 

 by J. Phillips, in Phil. Mag. April, 1849, and Amer. Journ. 

 (2) viii. 96-102, 258-263. 



Carbonic Oxide. — Filhol gives a convenient and economical 

 method of obtaining this gas (Journ. de Pharm. efde Ch. viii. 

 99), which consists in gently warming a mixture of 1 pt. sugar 

 or starch with 4 pts. by weight of oil of vitriol, and passing 

 the generated gas through milk of lime or potassa, to absorb 



