1. Silver, holding in 100 marcs, 7 marcs and 3
loths of alloy 24 to 30 marcs.
2. Pure litharge, containing from 88 to 90 per
cent. of lead 50 - 60 quintals.
3. Impure litharge, holding a little silver 2 - 6 --
4. Skimmings of the cupellation 4 - 8 --
5. Floor of the furnace impregnated with litharge 22 - 30 --
NOTE.--_The marc is 7 oz. 2 dwts. 4 gr. English troy; and the loth is
half an ounce. 16 loths make a marc. 100 pounds Cologne are equal to 103
pounds avoirdupois; and the above quintal contains 116 Cologne pounds._
The loss of lead inevitable by this operation, is estimated at 4 parts
in 100. It has been diminished as much as possible in the Frankenscharn
works of the Hartz, by leading the smoke into long flues, where the lead
fumes are condensed into a metallic soot. The silver cake receives a
final purification at the Mint, in a cupel on a smaller scale.
From numerous experiments in the great way, it has been found that not
more than 100 quintals of lead can be profitably cupelled at one
operation, however large the furnace, and however powerful and
multiplied the bellows and tuyères may be; for the loss on either the
lead or the silver, or on both, would be increased. In one attempt, no
less than 500 quintals were acted on, in a furnace with two fireplaces,
and four escapes for the litharge; but the silver remained disseminated
through the lead, and the _lightning_ could not be brought on. The chief
object in view was economy of fuel.
_Reduction of the Litharge._--This is executed in a slag-hearth, with
the aid of wood charcoal.
Such is the train of operations by which the cupriferous galena
_schlich_, or ground ore is reduced, in the district of Clausthal, into
lead, copper, and silver. The works of Frankenscharn have a front fully
400 feet long.
[Illustration: 1012 _Silver-smelting Works of Frankenscharn, near
Clausthal._]
_Fig._ 1012. exhibits the plan and elevation of these smelting-works,
near Clausthal, in the Hartz, for lead ores containing copper and
silver, where about 84,000 cwts. of _schlich_ (each of 123 Cologne
pounds) are treated every year. This quantity is the produce of 30
distinct mines, as also of nearly as many stamp and preparation works.
All these different _schlichs_, which belong to so many different
joint-stock companies, are confounded and worked up together in the same
series of metallurgic operations; the resulting mixture being considered
as one and the same ore belonging to a single undertaking; but in virtue
of the order which prevails in this royal establishment, the rights of
each of the companies, and consequently of each shareholder, are
equitably regulated. A vigorous control is exercised between the mines
and the stamps, as also between the stamps and the smelting-houses;
while the cost of the metallurgic operations is placed under the
officers of the crown, and distributed, upon just principles, among the
several mines, according to the quantities of metal furnished by each.