208 NICKEL. 
left alone at the bottom, in a metallic state. After 
the operation is complete, the oxide is fused with char- 
coal, and again reduced to metallic lead. 
We must not omit to mention that, in some of the 
mines of Derbyshire, there is a singular variety of lead 
ore called slickenside. This is a kind of galena, which 
presents, to the eye, a smooth and bright surface, ap- 
pearing as if it were plated. Sometimes it forms the 
sides of cavities ; and it has the extraordinary property, 
when merely pierced with the miner's tool, of rending 
with great violence, and exploding with a crackling 
noise. Some miners, fearless of danger, venture to 
scratch it with their tools ; and, on coming again to the 
spot, they often find that, during their absence, the 
slickenside has exploded, and fallen off in considerable 
quantity. Sometimes, however, they suffer for their 
imprudence. Mr. Mawe, in his account of the Mi- 
neralogy of Derbyshire, says, that he has seen a man 
come out of a mine cut violently, as if he had been 
stabbed about the neck and in other parts of the body, 
in consequence of the explosion of slickenside which 
he had pierced. The cause of this extraordinary 
phenomenon has not been explained. 
240. NICKEL, when pure, is a fine white metal, somewhat 
resembling silver in appearance, lut it is attracted by the 
magnet, and has itself the property of attracting iron. 
It is ductile and malleable, difficult of fusion, and about 
nine times heavier than water. This metal is always mixed 
with arsenic (242) and iron. 
Nickel is found in Cornwall, and in some other 
counties of England ; in Germany, Sweden, France, 
Spain, and several parts of Asia. The Chinese employ 
it in making white copper ; and, in conjunction with 
copper and zinc, they manufacture it into various kinds 
of children's toys. Nickel gives a certain degree of 
whiteness to iron. It is used, with advantage, by some 
of the Birmingham manufacturers, in combination with 
that metal, and by others in combination with brass. If 
