This substance, called by mineralogists “plumbago” and “graphite,”
is found in small quantities in various districts, and in a very
pure state in Cumberland. It is almost pure carbon, having but a
very slight admixture of iron; it is used to make blacklead pencils;
for coating the surface of iron, giving it a bright appearance and
preventing it from rusting; it is also used to prevent friction in
wooden machinery, and, mixed with tallow, as a lubricate for iron
machinery; blacklead, mixed with clay, is also used to make crucibles
for various purposes, these are especially adapted for melting
glasses and enamels, and are known in the trade as blue pots.