es, which allow the finest powder
to go through, the coarse being returned to the mill. When the one
happens to be mixed with copper or other metals which prevent
its reduction to powder, it is roasted or calcined in an oven or
reverberatory furnace, and pounded over again.

At the smaller mines, where they only use grindstones, they, for the
most part, grind the ore along with water, forming it into a liquid
paste, which runs out into receivers. When grinded dry, it has to be
afterwards mixed with water, and well moulded up with the feet for a
long time. For this purpose, they make a court or floor, on which that
mud, or paste of pounded ore and water, is disposed in square parcels
of about a foot thick, each parcel containing half a _caxon_, or
chest, which is twenty-five quintals or hundred-weights of ore, and
these parcels are called _cuerpos_, or bodies. On each of these they
throw about two hundred-weights of sea-salt, more or less, according
to the nature of the ore, which they mould or incorporate with the
moistened ore for two or three days. They then add a certain quantity
of quicksilver, squeezing it from a skin bag, to make it fall in drops
equally on the mass or _cuerpo_, allowing to each mass ten, fifteen,
or twenty pounds of quicksilver, according to the nature or quality of
the ore, as the richer it is, it requires the more mercury to draw it
to the silver contained in the mass, so that they know the quantity
by long experience. An Indian is employed to mould or trample one
of these square cuerpos eight times a-day, that the mercury
may thoroughly incorporate with the silver. To expedite this
incorporation, they often mix lime with the mass, when the ore happens
to be what they call greasy, and in this great caution is required,
as they say the mass sometimes grows so hot that they neither find
mercury nor silver in it, which seems quite incredible. Sometimes also
they strew in some lead or tin ore, to facilitate the operation of the
mercury, which is slower in very cold weather; wherefore, at Potosi
and Lipes, they are often obliged to mould or work up their cuerpos
during a month or six weeks; but, in more temperate climates, the
amalgama is completed in eight or ten days. To facilitate the action
of the mercury, they, in some places, as at Puno and elsewhere,
construct their _buiterons_ or floors on arches, under which they keep
fires for twenty-four hours, to heat the masses or _cuerpos_, which
are