The Yale expositor., 1909-06-04
HOW THE MANUFACTURE OF
WHITE LEAD HAS BEEN
REVOLUTIONIZED IN
MICHIGAN.


of the country. Strange it is, therefore
that with the exception of the milo
prOcess the methods of manufacture
of white lead have not kept pace will
the improvement in methods in othel
important industries of modern times
The process in general use is very old
was used before the time of Christ
and the Dutch have used it.for centur
les. 1t is largely a "rule of thumb
process because its different stages are
subject to but little control and the
product is not at all uniform.
THE OLD DUTCH PROCESS.
Under the old Dutch process the leaC
is moulded into discs weighing about
one pound each, and from sixteen e
eighteen of these discs placed in meta
pots containing acetic acid. These pots
are arranged in layers, piled one upon
another, board floors separating the
different layers, each one of which rests
upon several inches of ground tan bark
which is also placed about the pots
These pots remain buried i'm the tan
bark for period averaging about 125
days, during which the chemical action
caused by the heat of the fermepting
tan bark, and the acid slowly converts
| is commonly termed white lead. y
| During all this time the lead is buried
and beyond the control of workmen.
In addition it is process requiring
heavy expense as much labor is EN-
ployed in taking down the stacks and
removing the pots of corrOded metal,
such as is also employed in building
them and conveying the metal. The
/ M int
been complete and requires a vigorous
treatment Of crushing, rolling, screen
ing, grinding and floating to separate
the partially corroded lead, tan bark
and metallic lead. This, in itself, is
also an expensive operation and not
entirely satisfactory. To the laymen
the difficulties and handicaps of this
process become at once apparent. 1t
is costly and incomplete, requiring the
use of great quantities of acids and ex-
pensive tan bark, pots, lumber, which
must constantly be replaced, and does
not develop satisfactorily.
THE NEW MILD PROCESS.
The change from this blind, uncer-
tain method of manufacture to the
positive, certain and easily controlled
Mild process, with its uniform product
of superior Wilderness, density and
covering power, marks an epoch in the
paint industrya long step ahead in
the manufacture of perfect paints for
all purposes" All of the drawbacks of
the "Old Dutch" are overcome in the
Mild Process which neither requires
acids, the burying of metal, the delay
of three months for fermentation pur-
poses, the expensive outlay for tan
bark, lumber, pots, etc, formerly need
ed. This saving alone would justify
the new process, but it has other ad-
vantages, the full theoretical chemical
increase of % per cent for metal cor
rosion being secured, as well as the
utilization of all parts of the pig lead,
which can be of the ordinary market
product and not "A special metal made
for this purpose.
The new process has passed the ex-
detrimental stage its product having
been in constant use for over five years
and thoroughly tested The story of
the process is a most wonderful one
and so simple child can understand
it.
The pig lead is first melted in big
furnaces and then drawn off in fluid
form into immense "atomizers" where
the stream of molten lead is literally
"blown into atoms" by powerful jets of
steam-so powerful that the lead is re-
duced to a very fine powder that feels
between the fingers like the finest pot
ters clay. This fine lead powder falls
from the atomizers into large tanks
partly filled with water where it col
lects on the bottom and is then pumped
into large drums called "oxidizins,"
equipped with powerful agitators,
which keeps the finely divided lead
from settling to the bottom, while
fresh air is constantly forced through
the liquid. The lead rapidly combines
with water and oxygen in the air,
forming what is chemically. known as
basic hydroxide of lead. 1t is then
passed through the separating system
that returns the unOxidized metal to
the oxidizers and sends the oxidized
lead to the larger "carbonating cylin-
der" In these cylinders the lead is
kept constantly agitated and stream
of purified carbondioxide gas is forced
slowly through the semi-liquid mass.
In about thirty-six hours the lead, com
bining with the gas, is converted into a
strictly pure carbonate of lead-the
white lead of commerce. The semi
liquid white lead paste is pumped oil
rectly from the carbonators into steam
iacketed copper pans. The heat rapid
ly dries out the lead which is then
ready to be ground in oil or packed in
dry form for shipment. No separating,
sorting, grading or remelting is neces
sary, for there are no impurities to be
removed and the lead is so soft that no
crushing is necessary before it is ground
in oil.
ADVANTAGES OF THE MILD PROCESS
OF MANUFACTURING WHITE LEAD.
Every step of the process is under
complete control, insuring an absolute
ly uniform and perfect product. No
conveying in wheel-barrows, no trans
ferring from one place to another by
manual labor is necessary. Gravity
does most of the work; the balance is
done by pumps, requiring little power
and no hand labor TO operate.
No acids or alkalis OF any kind are
used, metallic lead, air, water and car.
bon dioxide gas only are employed.
Consequently there are no impurities to
be removed from the finished product,
no Off-grade lead TO be blended in or
sold af rpdupad pripao No nv. nroduptc