LEAD. 203 
used for the silvering of looking-glasses are much 
thicker. The article called tin-foil is an alloy, consist- 
ing generally of two parts of tin and one of lead ; and 
capable of being beaten to less than the thousandth 
part of an inch in thickness. 
239. LEAD is a heavy metal, of pale and livid grey colour 
when broken, not sonorous when pure, very flexible, and so 
soft that it may be marked with the nail. It stains paper or 
the Jingers of a bluish colour, and is about eleven times heavier 
than water. 
The most common state in which lead is found is in combi- 
nation with sulphur and a small portion of silver. This ore 
is known by the name of galena, and is frequently in the form 
of blackish cubical crystals. Lead is also found in union with 
arsenic (342) and many acids, 
Great Britain possesses the most important lead- 
mines in the world; and those that are best known are 
in the counties of Flint and Derby. The latter are 
supposed to have been worked even in the time of the 
Romans. 
Lead mines are entered sometimes by perpendicular 
shafts, and sometimes (when in the sides of hills) by 
levels. In some of the Derbyshire mines, where the 
depth of the veins will admit of it, the men work, at 
different heights, of from four to six feet above each 
other, along what are called stoops; the uppermost 
men being two or three yards before those next in 
succession, and thus forming a kind of steps. The 
implements used are picks, hammers, and strong iron 
wedges ; and the rocks are also frequently loosened by 
means of gunpowder. 
When the ore is brought out of the mine, it is sorted 
and washed, to free it from dirt and rubbish. After 
this it is spread on a board ; the best pieces are picked 
out and separated ; and those containing ore mixed with 
spar (194-) or other substances, are placed separate, to 
be broken, and again picked. After the ore, by picking 
and washing, has been sufficiently cleansed from ex- 
traneous matters, it is roasted in a kind of kiln to free 
