A wall which will be called the "second wall " is constructed of brick
or stone, two feet and as many palms thick, in order that it may be strong
enough to bear the weight. It is built fifteen feet high, and its length depends
on the number of furnaces which are put in the works ; there are usually
six furnaces, rarely more, and often less. There are three furnace walls, a
back one which is against the " second " wall, and two side ones, of which I
will speak later. These should be made of natural stone, as this is more
serviceable than burnt bricks, because bricks soon become defective and
crumble away, when the smelter or his deputy chips off the accretions which
adhere to the walls when the ore is smelted. Natural stone resists injury
by the fire and lasts a long time, especially that which is soft and devoid
of cracks ; but, on the contrary, that which is hard and has many cracks
is burst asunder by the fire and destroyed. For this reason, furnaces which
are made of the latter are easily weakened by the fire, and when the accretions
are chipped off they crumble to pieces. The front furnace wall should be
made of brick, and there should be in the lower part a mouth three palms
wide and one and a half feet high, when the hearth is completed. A hole
slanting upward, three palms long, is made through the back furnace wall, at
the height of a cubit, before the hearth has been prepared ; through this
hole and a hole one foot long in the " second " wall—as the back of this wall
has an arch—is inserted a pipe of iron or bronze, in which are fixed the nozzles
" bronze age " prior to recorded civilization, starting with the savage who accidentally
built a fire on top of some easily reducible ore, and discovered metal in the ashes, etc. ; but
as this method has been pursued times out of number to no particular purpose, we will
confine ourselves to a summary of such facts as we can assemble. " Founders' hoards "
of the bronze age are scattered over Western Europe, and indicate that smelting was done
in shallow pits with charcoal. With the Egyptians we find occasional inscriptions showing
small furnaces with forced draught, in early cases with a blow-pipe, but later—about 1500
b.c.—with bellows also. The crucible was apparently used by the Egyptians in secondary
melting, such remains at Mt. Sinai probably dating before 2000 b.c. With the advent of the
Prophets, and the first Greek literature—9th to 7th century B.c.—we find frequent references
to bellows. The remains of smelting appliances at Mt. Laurion (500-300 B.c.) do not indicate
much advance over the primitive hearth ; however, at this locality we do find evidence of
the ability to separate minerals by specific gravity, by. washing crushed ore over inclined
surfaces with a sort of buddle attachment. Stone grinding-mills were used to crush ore from
the earliest times of Mt. Laurion down to the Middle Ages. About the beginning of the
Christian era the writings of Diodorus, Strabo, Dioscorides, and Pliny indicate considerable
advance in appliances. Strabo describes high stacks to carry off lead fumes ; Dioscorides
explains a furnace with a dust-chamber to catch pompholyx (zinc oxide) ; Pliny refers to the
upper and lower crucibles (a forehearth) and to the pillars and arches of the furnaces. From
au of their descriptions we may conclude that the furnaces had then reached some size, and
were, of course, equipped with bellows. At this time sulphide copper and lead ores were
smelted ; but as to fluxes, except lead for silver, and lead and soda for gold, we have practically
no mention. Charcoal was the universal fuel for smelting down to the 18th century. Both
Dioscorides and Pliny describe a distillation apparatus used to recover quicksilver. A formidable list of mineral products and metal alloys in use, indicate in themselves considerable
apparatus, of the details of which we have no indication ; in the main these products were
lead sulphide, sulphate, and oxide (red-lead and litharge) ; zinc oxide ; iron sulphide, oxide
and sulphate ; arsenic and antimony sulphides ; mercury sulphide, sulphur, bitumen, soda,
alum and potash, ; and of the alloys, bronze, brass, pewter, electrum and steel.
From this period to the period of the awakening of learning our only light is an
occasional gleam from Theophilus and the Alchemists. The former gave a more detailed
description of metallurgical appliances than had been done before, but there is little vital
change apparent from the apparatus of Roman times. The Alchemists gave a great stimulus
to industrial chemistry in the discovery of the mineral acids, and described distillation apparatus
of approximately modern form.
The next period—the Renaissance—is one in which our descriptions are for the first
time satisfactory, and a discussion would be but a review of De Re Metallica.
