Sacramento daily record-union., 1890-09-20
WAITE LEAD.
INTERESTING FACTS ABOUT ITS MANU-
FACTURE.
Slow Process by Which 1t is Produced
why the Best Quality Comes
so High.
From the American Analyst !

from the American Audlysl.
White lead, as it is offered to the painter
ground in oil, is carbonate of lead,
called a hydrated carbonate of lead in
chemistry, because it contains proportion
of water held in chemical combination.
This particular chemical combination can
not be brought about by immediate and
quick chemical reaction, but must be ac-
complished by slow processes covering
eight or twelve weeks. A carbonate of
lead may be formed by making the me-
tallic lead into solution and precipitating
at once by the introduction of carbonic
acid, but such carbonate of lead would
contain SO large a percentage of carbonic
acid as to unfit it for use as pigment. 1t
is desirable to obtain carbonate of lead
which shall have the largest proportion of
lead in perfect chemical union with the
least carbonic acid, and this is accomplished
as set forth below. Metallic lead of the
greatest purity is used; this is obtained
| from our argentiferous (silyer- bearing ores)
| or galena The silver being first ex-
| tracted, having then the pure lead cast
into pigs for convenience in handling
weighing generally go to 100 pounds each,
the first step in the process is casting
The pigs are placed in heavy iron ket-
| tie or crucible, under which is kindled a
fire of sufficient temperature to melt the
lead. When melted to such degree as to
run in small stream from the kettle, an
opening is made by means OF valve near
the bottom Of the kettle, and the lead is
allowed to flow in a continuous stream
therefrom, falling upon molds so linked to-
gether as to form an endless revolving
belt or chain, each mold constituting a
link in the chain and being hinged to the
next. This chain of molds is made to pass
in lateral direction away from the kettle
to such distance as to insure the harden
ing of the lead by cooling, when it passes
around pulley, dropping out the nodded
| lead as it is inverted Continuing on
around second pulley, the molds are
again right side up, and receive their
| charge from the stream of molten metal
| These castings OF lead are called buckles
from the fact of their having somewhat
| the appearance OF buckle in shape. They
are made in thickness from an eighth to
nearly half an inch. Insted of having a
square shape, as buckles in general. the
outer circumference is round, and the
tines, as they might be called, reach all
the way across and are united at both ends
with the outer rim, which is from four to
six inches in diameter. The openings be-
tween the tines and the outer rings admit
of free circulation of air when placed in
stacks for corrosion, and the thinness OF
the buckles presents the more surface to
the action of the chemicals. In fact, these
castings are made for the sole purpose OF
obtaining the greatest possible surface OF
lead in a given quantity for the free and
more rapid action of the chemical yapors.
Having now the lead cast into small
buckles, the next step is setting these
pieces of lead in the stacks or beds for cor
rosion.
/ For convenience in handling and in
order that the lead may not be pressed too
closely together by its weight, small
earthen pots are used in which to place it.
These pots are constructed expressly for
this use. They are generally about nine
inches high, eight inches wide across the
top, and taper to about FIVE inches across
the bottom having the appearance of large
flower pots. Two openings of about two
inches in diameter are made in opposite
sides of the pot, and one higher than the
other to allow a circulation of vapors and
inside the pot about one-third its hight,
are three or four projecting knobs, upon
which the lead rests without being placed
in the bottom of the pot. A corroding
house, or bed, as it is sometimes called
generally built of wood, from twenty to
thirty feet square, constructed with four
sides and floor only, one roof covering a
number of them, has spread upon its floor
frem twelve to fifteen inches of spent tan
bark, obtained from tannery after it has
served the purpose of tanning leather.
Upon this layer of tanbark the pots are
placed as closely together as possible until
the whole layer of tan is covered by them.
The next step is to pour into each pot
about half pint of vinegar weak acetic
acid, which fills the pot below the pro-
jecting knobs only. The buckles of lead
are then placed in the pots, filling them
from the knobs to the top By this means
the lead is above the acid without coming
in contact with it. The pots, all being
filled with acid and lead, are then covered
with layer of boards, which form a sec.
ond floor, upon which another layer OF
tanbark is spread, followed by second
layer of pots until eight or ten layers have
been set and the bed or corroding house is
full TO the top, finishing with layer OF
tanbark. A yentilating hue, about four
inches square, and running from the bot
tom layer out of the top of the corroding
house, is placed either in the middle or to
one side of the house. The setting is now
complete and the chemical action, called
corrosion, begins. The first occurrence is
the fermentation of the bark, which has
been placed in the bed wet. This fer
mentation generates carbonic acid gas, and
at the same time creates sufficient heat to
raise the temperature of the whole to
about 1909. The elevation of temperature
causes evaporation of acetic acid. The
vapor, rising in the pots, is circulated
through the buckles of lead coming in con-
tact with their surfaces and slowly forming
an acetate of lead.
Carbonic acid, which has no affinity for
combining with metallic lead, combines
readily with acetate of lead, displacing
acetic acid, which passes away through the
ventilating fue, and taking is place in
combination with the lead, which is now
carbonate of lead. Were it possible to
unite carbonic acid and metallic lead di-
rectly, there would be no necessity for the
use Of acetie acid; but this being imprac-
ticable, acetic acid is used to bring about
the union of the carbonic acid and the
lead, and having performed its part, it
escapes through the flue into the open air.
! The corrosion of the lead, as above stated,
begins upon the outside of the buckle and
gradually works its way inward, until all
! the lead becomes converted into carbon
ate-that is, if the corrosion is complete,
which is seldom the case Generally, upon
| opening the corroding house at the expira-
ton of three months, about 65 per cent.
only (by weight of the metallic lead is
! found 10 have been corroded. the remain