William Champion's zinc process (1825)
Producing metallic zinc
This is the first known description of William Champion's zinc process. It appeared in the Annales des Mines, Tome X, 1825. The present edition was translated directly from the original French.
Figure 1 - general description
The furnace is round and covered with a cone which acts as a chimney.
The cone surrounding the furnace has as many openings as there are
- a-a small walls which are removed at will to put in or take out the pots. They
are made of bricks, with a hole through which an iron bar can be
inserted so the pots can be moved whilst still hot.
- b firedoor, closed with a brick.
- c ashpit in which the workman enters to clean the fire bars.
- d-d holes, formed in the upper part of the furnace dome, to permit entrance of
the flames into the chimney. The pots are also charged through these
holes. They are never closed all at the same time. The workmen can,
by closing some of them, direct the fire to any part of the furnace.
- e-e, e-e passages in the foundation corresponding to the pots.
- g-g containers, in sheet-iron, for the zinc.
- h cylindrical sheet-iron tube to be fitted to the condenser, conducting the zinc
into the container.
<>i condenser. This a slightly conical sheet-iron tube, with a flange at its upper
end by which it is attached to the pot. To secure it, a ring of
fireclay is placed on the flange and it is then pressed strongly
against the pot. To maintain it in this position, two iron rods k-k
are fixed to the lower part of the condenser by a collar. These pass
through little pieces of iron m, mounted into the wall. The rods are
then locked with the clamp screws n.
- 1-2 level of the upper floor
- 3-4 level of the lower ceiling
- 5-6 level of the lower floor
Figure 2 - Half-plan on the level 1-2.
Figure 3 - Vertical section of a pot and the equipment which is used to secure the
condenser against the pot.
Figure 4 - Wheeled tongs for transporting the hot pots.
Figure 5 - Half-plan on the level 3-4.
Note that the passages in the foundation are in double-cross form, to
accommodate condensers and containers for six pots.
Most of the works where [metallic] zinc is manufactured are
situated in the neighbourhoods of Birmingham and Bristol. This
presumably is caused by the fact that the [much older] direct
manufacture of brass [from copper and calamine], has for a
long time been concentrated in these two towns. So it is perhaps not
strange that, at the time when they began to make brass by alloying
[copper] with metallic zinc instead of calamine, the new
industry was also located at these places. There are some zinc
furnaces in the neighbourhood of Sheffield, too, on the nearby
The works at Bristol and Birmingham are principally supplied [with
ore] from workings at Mendip and in Flintshire. The Sheffield
furnaces draw their calamine from Alston-Moor in Cumberland.
Roasting of calamine
The calamine, from which any galena has first been separated by
sorting, is roasted before being put in a reduction furnace. Roasting
is done in a reverberatory furnace of about 10 ft long by 8 ft wide.
The ore, coarsely crushed, is placed on the sole of the furnace in a
bed about 6 inches thick.
In some works, the ore is not roasted and the calamine, broken to the
size of pigeon-eggs, is mixed with an equal volume of small coal.
The reduction process
The reduction furnaces are rectangular or round. They hold 6 or 8
pots. Round furnaces are the most advantageous for working. They
usually contain only 6 pots, as is shown on the Plate, in the Figures
1 and 2. The pots are inserted in the furnace after removing the
small walls a-a. When the pots are replaced whilst the furnace is
(still) hot, they are pre-heated in a special furnace. This has a
sole on which the pot is placed and on each side it has a small
fire-place. The heated pot is taken out, moved and positioned in the
zinc furnace by means of tongs mounted on two iron wheels, as shown
in Figure 4. The pots are made of fireclay. They have a hole in the
bottom, through which the zinc runs into the condenser. Prior to
charging the pots, this bottom hole is closed by means of a suitable
piece of wood. During smelting, the wood will be converted to
charcoal. This stop prevents the mixture, charged from above, from
flowing out of the pot.
The hole in the lid of the pot, see Figure 3, is left open for about
two hours after charging, until the blue colour of the flame
indicates the beginning of the reduction. At this point the hole is
closed with a plaque of fireclay. Next, the sheet-iron tubes are
fastened to the ends of the condensers and into the sheet-iron
containers which will receive the molten zinc. Sometimes, these
containers are filled with water to prevent the falling zinc from
During the time a charge is being worked, the only task of the
workmen is to feed the fire and to keep clear the condensers. These
are sometimes blocked with zinc, which collects in great abundance.
Opening up the condensers is done by means of a red-hot bent iron
bar, inserted into the condenser from below.
The zinc collected during smelting is in the form of droplets and
fine powder, and mixed with zinc oxide. This mixture is remelted in
an iron pot, placed on a special hearth. The oxide floats as a dross
on top, it is skimmed from the surface to be placed in the pots
again. The metal is cast into ingots.
To empty the pots at the end of each reduction operation, the
condenser is removed, the stop of charcoal in the bottom hole of the
pot is then broken away completely with a clinker bar and the ore
residue falls out when it is stirred from above. When replacing the
condenser, they put a little ring of damp fireclay on its flange, see
Figure 3, and press it against the bottom of the pot. It is kept in
position by means of small rods.
Workforce, output and costs
Three men are employed to work a furnace, a foreman and two
labourers. They themselves make the pots. A mixture is used of equal
parts of fresh fireclay and of calcined clay, the latter from the
debris of old pots. The average life of pots in the reduction furnace
is four months.
Five charges are made in fifteen days. In these five charges 6-10
[metric] tons of calamine and 22 - 24 [metric] tons of
coal are used. About 2 [metric] tons of zinc are produced.
One can roughly calculate the cost of a [metric] ton of zinc
at Bristol, as follows.
|3 tons of calamine @ £ 6
|24 tons of coal @ 5 s.
|a foreman @ 6 s. a day, for 7 days
|two labourers @ 4 s.
|cost of a ton of zinc at Bristol
The calamine from Alston-Moor, used at Sheffield, is less rich. At most it produces 25% zinc. The coal there costs 5s. 8d. per ton and the calamine, delivered at
the works, costs £ 5 [a ton]. From this, Sheffield zinc costs £ 32 14s. per ton.
These are of course cost prices, the zinc actually is sold to the customer for £ 40 to £ 44.
Imported zinc is sold at the London docks for £ 20 to £ 24. This
enormous difference is caused partly by the high price of calamine.
One is not surprised to learn that this metal has an import duty of
Use of blende instead of calamine
In England zinc is also made from blende. This mineral, washed and
crushed to nut-size is sold at Holywell, at the mine, for £ 3
per ton, or about half the price of calamine.
It is roasted, without any other preparation, in a reverberatory
furnace. These furnaces are about 8 ft wide by 10 ft long. The height
of the vault from the sole is 30 inches. The height of the fire
bridge [over the sole] is 18 inches.
The bed of blende is about 4 - 5 inches thick. It is stirred almost continuously.
The consumption of coal is 4 tons for each ton of roasted blende. The
loss [in metal] is 20%. The operation lasts 10 or 12 hours.
The mixture to be smelted is made up of a quarter roasted blende, a
quarter roasted calamine and a half of coal. It commonly gives 30%