METALLURGY. For the specific treatment of the ores of copper, gold, iron, silver, tin, zinc, etc., see the articles on those metals.
As now understood metallurgy is the art of extracting metals from their ores. The operations are partly mechanical and partly chemical. Those processes which depend principally on chemical re actions for their results have reference chiefly to the roasting and smelting of ores, and are described under the heads of the different metals. But there are certain preliminary operations of a me chanical kind which metallic ores under go, such as crushing, jigging, washing, etc., which we shall describe here, as they are essentially the same for the ores of lead, copper, tin, zinc, and indeed most of the metals. Till comparatively recent times ore, or rather ore-gangue, asit came from the mine was in the first . stance broken by hammers before being passed on to crushing rollers or stamps to be reduced to smaller pieces or grains. In the year 1858 Mr. E. W. Blake of New Haven, Conn., invented a stone or ore crusher which has become so extensively used that it has, except in special cases, superseded hand labor for breaking up large pieces of ore. After passing
through this or some similar crusher, the vein stuff or impure ore is next taken either to the crushing rollers or to the stamping mill.
In recent years there has been con tinued improvement in the methods of carrying on metallurgical processes. The conditions produced by the war called for a production of iron and steel on an immense scale, and many improvements were devised to produce this result. One of the most important was the synthetic cast made from steel turnings by melting in an electric furnace in contact with coke. By this process power consump tion was more than double and iron of a very high degree of purity is obtained. The use of electric furnaces continued to increase. Especially in the treatment of non-ferrous metals, some important im provements were made in the designs of blast furnaces in 1917. See MINERAL ''RODUCTION, UNITED STATES.