HYLURGY. 435 



When used for cooking, it should be tinned over ; as its rust and 

 salts are poisonous. Tin, is a white metal, which produces a pecu- 

 liar crackling sound when bent. It is used sparingly, for coating 

 iron or copper; and for forming, with copper, bell-metal and bronze. 

 Lead, is a heavy, but soft, bluish metal, easily tarnished, and, like 

 tin, easily melted. It is poisonous internally; but there are few 

 substances which will dissolve it: and it is much used for covering 

 roofs and cisterns, and forming water pipes. Zinc, is a hard and 

 brittle metal ; though ductile when hot ; and melting at a heat below 

 redness. With copper, it forms brass, and pinchbeck. 



Metallurgy, properly comprises the reducing of the metals from 

 their ores, and the elementary processes of working them. Most of 

 the metals are obtained from their oxides, sulphurets, or chlorides, 

 by smelting ; that is by heating them with charcoal, or coke, and 

 adding sometimes a flux, as of lime, or sand, to react upon the ores, 

 and fuse them. The charcoal combines with the oxygen, and thus 

 separates the metal ; which, in most cases, runs down, and is drawn 

 out from the furnace. The sulphurets and chlorides, by roasting, 

 or heating in the air, are converted into oxides ; and then reduced as 

 above explained. The furnaces used, are either draught furnaces, 

 which burn by the natural draught ; or blast furnaces, into which 

 the air is driven by bellows, or by machinery. Reverberatory fur- 

 naces, have arched roofs, to reflect the flame back upon the ores. 

 Among the processes of working iron, are casting, from the impure 

 melted iron first obtained ; forging, or purifying cast iron, which is 

 brittle, and hammering it into wrought iron, which is malleable ; 

 rolling and drawing wrought iron into sheets, bars or wire ; and the 

 converting of iron into steel, by combining it with a due portion of 

 carbon. The worker in rough iron is called a blacksmith : but the 

 filing and polishing of iron or steel is the work of the whitesmith ; 

 and the worker in lead is called a plumber. 



The art of Mining, or procuring metallic ores, mineral coal, and 

 rock salt, from mines dug in the earth, supposes a knowledge of 

 Geology , and often requires the aid of Machinery and Civil Engi- 

 neering. Mines, are worked, either by sinking a shaft, or pit, like 

 a well, and drawing up the materials, by means of a wheel and axle, 

 or other machinery ; or, when lying beneath a considerable slope, 

 they are entered by tunnels ; commencing, externally, on the level 

 of the bottom of the mine, or lower, in order to draw off the water 

 which may infiltrate. The minerals sought, lie sometimes in veins ; 

 but oftener in beds, or in successive thin strata ; requiring the removal 

 of much superfluous matter. The occurrence of a fault, where the 

 beds are broken across, and one part raised above the other, often 

 perplexes the miner, and interrupts the work. 



2. The Earthy Materials, used in the arts, are principally stones, 

 clay, sand, and lime ; used chiefly for building. In this relation, 

 stones may be classified as either calcareous, containing lime, or its 

 metallic base ; or siliceous, containing sand or silicic acid. Of cal- 

 careous stones, the most important is marble, which is simply crys- 

 tallized limestone ; it being easy to cut, and in mild climates suffi- 

 ciently durable, though gradually disintegrated by frost. Gypsum, 



