A NEW METHOD OR METHODS OF MAKING CERUSE, OR WHITE LEAD
Year: 1797

page_text: THE EARL OF DUNDONALD'S SPECIFICATION.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ARCHIBALD,
EARL OF DUNDONALD, send greeting.
WHEREAS His most Excellent Majesty King George the Third, by His
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the Eighteenth day of August now last past, did give and grant
unto me, the said Archibald, Earl of Dundonald, my executors, administrators,
and assigns, His said Majesty's special licence that I, the said Archibald, Earl
of Dundonald, my executors, administrators, and assigns, during the term of
years therein mentioned, should and lawfully might make, use, exercise, and
vend, within England, Wales, and the Town of Berwick-upon-Tweed, my
Invention of "A NEW METHOD OR METHODS OF MAKING CERUSE, OR WHITE
LEAD;" in which said Letters Patent there is contained a proviso obliging
me, the said Archibald, Earl of Dundonald, by an instrument in writing under
my hand and seal, particularly to describe and ascertain the nature of my
said Invention, and in what manner the same is to be performed, and to
cause the same to be inrolled in His said Majesty's High Court of Chancery
within one calendar month next and immediately after the date of the said
recited Letters Patent, as in and by the same, reference being thereunto had,
will more fully and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Archibald, Earl of Dundonald, do hereby declare that my said Invention, as to
one method or process thereof, is described in manner following; that is
to say:
Lead is to be brought to the state of a calx or oxyd; the calx is to
be mixed with muriat of potash, or sal degestions silvii, or with the oxygenated
muriat of potash, or with the solution of either of these salts, in the proportion
which shall be found requisite; this, for the most part, may be reckoned at
one part of salt, by weight, to five parts of the calx of lead. The materials
are to be intimately mixed, by grinding or otherwise, and are to be stirred at
different times, to expose fresh surfaces to the action of the air, and are to be
alternately wetted with water (either impregnated or not with fixable air or
carbonic acid), and dried by exposure to atmospheric air, or to any air in
which carbonic acid is contained, until the compleat action of the materials,
the one or the other is effected. In this state they consist of a ceruse, or
white lead, or carbonet of lead, and muriat of potash. The muriat of potash
is, by washing, to be separated from the ceruse or white lead, to be concen-
trated by evaporation, and to be preserved to act again on more of the calces
of lead. Lastly, the white lead is to be ground, levigated, and dried. It is
proper here to state, that muriat of potash, or salt of silvius, has in most
chemical treatises been represented to be of little or no use in the arts; and as
it is a salt which very rarely occurs as a residuum from chemical mixtures or
combinations, it might the more easily escape the notice and experiments of
chemical persons, or of persons in search of discoveries connected with different
branches of manufacture. Muriat of potash possesses properties different from
muriat of soda or sea salt, and in the present instance produces a change on
the calces of lead not effected when muriat of soda only is used. The appli-
cation of muriat of potash to the calces of lead, for the production of ceruse or
carbonet of lead, is not therefore to be confounded with the attempts of others
to produce a carbonat of lead by the mixture of muriat of soda with the calces
of lead. When the muriat of potash, or, more properly speaking, its solution,
is mixed with the calx of lead, a change takes place; the vegetable alkali of
the muriat of potash is disengaged in a caustic state, while the muriatic acid
enters into combination with the calx of lead, and forms muriat of lead. By
exposure of the materials to atmospheric or to air containing the carbonic acid,
this acid is attracted by the caustic vegetable alkali, and as it is received is
transmitted to the lead, forming therewith a carbonat of lead or ceruse, while
in return the alkali takes back from the muriat of lead the muriatic acid in a
state more oxygenated than that in which it existed in the muriat of potash

page_text: when first applied. The muriat of potash recovered is to be applied for
making with the calces of lead more ceruse or carbonat of lead. It has been
found most advantageous not to use the calx of lead very highly calcined. In
this highly calcined state I generally use a small proportion of lead in a
metalic state along with the calx. The process of mixing lead with the calx
or calces of lead for making with muriat of potash, ceruse or carbonate of lead,
is to be included under the Patent to which this Specification refers.
And I do hereby further declare, that the other method or process for making
ceruse or white lead, for which the Letters Patent herein-before recited have
been obtained, is as follows; that is to say:-In this method or process, muriat
of soda or sea salt is to be substituted for muriat of potash, and it or its solution
is to be mixed in the same manner with calx or calces of lead in the first pro-
cess or method herein-before mentioned. To this mixture, after the proper
degree of action has taken place, a sufficient quantity of vegetable alkaline salt
is to be added, to give or procure to the lead the carbonic acid, which is more
speedily done when the vegetable alkali is in a state of carbonat. The salts
are then to be separated from the ceruse or carbonat of lead by washing of the
two salts, consisting of soda or mineral alkali and muriat of potash, are to be
separated; or the soda may be separated before the potash is added to the
materials. Lastly, the ceruse or carbonat of lead is to be levigated and dried.
The muriat of potash, when separated, is to be preserved, and applied to
operate on more of the calx or calces of lead; and this comes under the
description given in the first method or process herein-before mentioned.
In witness whereof, I, the said Archibald, Earl of Dundonald, have
hereunto set my hand and seal, the Sixteenth day of September, in
the year of our Lord One thousand seven hundred and ninety-seven.
Inrolled the Eighteenth day of September, in the year above written.