228 INDUSTRIAL MINERALS DIAGRAM 19 



tained by more or less complicated processes. Metallurgy is the 

 name given to these operations. 



Ores sometimes form considerable deposits, but they are 

 generally arranged in thin layers called veins or lodes. These 

 veins are often several leagues in length, by a breadth which 

 does not exceed a few inches. Most veins form hard masses, 

 which are worked by being Hasted with powder. The mines 

 which are dug to procure them are not generally subject to the 

 same dangers as coal mines, but are often difficult to work on 

 account ol the hardness of the rock in which the veins are em- 

 bedded. 



Iron ore. This is often met with at the surface of the ground, 

 and is nearly always of a red colour similar to that of rust. To 

 obtain the iron, the ore is thrown .into very hot furnaces, 

 called smelting furnaces. Coal is thrown in at the same 

 time, and the molten metal is collected at the bottom of the 

 furnace, where it flows into trenches of sand, and cools in masses 

 which are called pig-iron or cast-iron. This cast-iron must be 

 melted again before it can be used. It is then made into a great 

 many articles such as grates and kettles, and it is also made into 

 stoves, but these ought to be used as little as possible because 

 they are unhealthy, and may even cause serious accidents to 

 persons who work in rooms and workshops heated by these 

 stoves. 



To work cast-iron it is put into the fire and when it is suffi- 

 ciently softened it is put under an enormous hammer, the blows 

 of which remove those substances called sconce which make it 

 brittle and easily fusible. Iron thus purified melts with diffi- 

 culty. It is not brittle, and can be forged at will, and it is 

 called soft iron When the iron ore contains a large proportion 

 of sulphur, the iron remains brittle after having been purified. 



To make steel, the iron is mixed with a proper proportion of 

 coal, and is heated to redness. Steel is brittle, but elastic 

 and very hard. These qualities can be increased by heating it 

 more or less, after which it is plungecf either into oil or into 

 water, to be suddenly cooled. This process is called tempering. 

 The uses of cast-iron, iron, and steel, are innumerable, 



