CHAP. 49.—BLACK LEAD.
is used in the form of pipes and sheets: it is extracted
with great labour in Spain, and throughout all the Gallic
provinces; but in Britannia2
it is found in the upper stratum of
the earth, in such abundance, that a law has been spontaneously
made, prohibiting any one from working more than a certain
quantity of it. The various kinds of black lead are known by
the following names—the Ovetanian,3
and the Oleastrensian.5
There is no difference whatever in
them, when the scoria has been carefully removed by calcination.
It is a marvellous fact, that these mines, and these only,
when they have been abandoned for some time, become replenished,
and are more prolific than before. This would
appear to be effected by the air, infusing itself at liberty
through the open orifices, just as some women become more
prolific after abortion. This was lately found to be the case
with the Santarensian mine in Bætica;6
which, after being
farmed at an annual rental of two hundred thousand denarii,
and then abandoned, is now rented at two hundred and fifty-
five thousand per annum. In the same manner, the Antonian
mine in the same province has had the rent raised to four
hundred thousand sesterces per annum.
It is a remarkable fact, that if we pour water into a vessel
of lead, it will not melt; but that if we throw into the water
a pebble or a copper quadrans,7
the vessel will be penetrated
by the fire.