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The specific gravity of the best wad, or black-lead, is, to that
of water, as two to one nearly: the coarser kind is heavier in
proportion, as it contains more stony matter. It comes from the
mine in pieces of irregular shape, and of various sizes,
requiring no process to prepare it for the market, further than
freeing the pieces from any stony or extraneous matter, which may
adhere to them. It is then assorted according to the different
degrees of purity and size, and thus packed in casks to be sent
off to the warehouse in London, where it is exposed to sale only
on the first Monday in every month.
In the year 1803, after a tedious search, one of the largest
bellies was fallen in with, which produced five hundred casks,
weighing about one hundred and a quarter each, and worth thirty
shillings a pound and upwards; besides a greater quantity of
inferior sorts; and since that time several smaller sops have
been met with; in the beginning of the year 1829, a sop produced
about half a dozen casks; the best part of which was eagerly
bought up at thirty-five shillings a pound. For three or four
years the quantity raised was trifling; but in 1833, they
succeeded in filling a few casks, the best part of which has been
sold at forty-five shillings a pound.
By an account published in 1804 the stock then on hand was valued
at £54,000, and the annual consumption stated to be about
£3,500. This
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