IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD, PART OF WHICH IMPROVEMENTS ARE APPLICABLE TO THE MANUFACTURE OF MAGNESIA AND ITS SALTS
Year: 1841

page_text: 10 ALL TO WHOM THESE PRESENTS SHALL COME, I, HUGH
LEE PATTINSON, of Bensham Grove, Gateshead, in the County of Durham,
Manufacturing Chemist, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the Twenty-fourth day of September, in the fifth year of Her reign,
did; for Herself; Her heirs and successors, give and grant unto me, the said
Hugh Lee Pattinson, Her especial licence, full power, sole privilege and
authority, that I, the said Hugh Lee Pattinson, my exors, adñiors, and
assigns, or such others as I, the said Hugh Lee Pattinson, my exors, admors,
or assigns, should at any time agree with, and no others, from time to
time and at all times during the term of years therein expressed, should.
and lawfully might make, use, exercise, and vend, within England, Wales, and
the Town of Berwick-upon-Tweed, my Invention of "IMPROVEMENTS IN THE
MANUFACTURE OF WHITE LEAD, PART OF WHICH IMPROVEMENTS ARE APPLICABLE
TO THE MANUFACTURE OF MAGNESIA AND ITS SALTS;" in which said Letters
Patent is contained a proviso that I, the said Hugh Lee l'attinson,
shall cause a particular description of the nature of my said Invention, and
in what manner the same is to be performed, to be inrolled in Her said
Majesty's High Court of Chancery within six calendar months next and
immediately after the date of the said in part recited Letters Patent, as in
and by the same, reference being thereunto had, will more fully and at large

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Hugh Lee Pattinson, do declare that my Invention consists in dissolving car-
bonate of magnesia in water impregnated with carbonic acid gas, by acting
upon magnesian limestone, orother earthy substances containing magnesia in
a soluble form, or upon rough hydrate of magnesia, in the mode afterwards
described, and in applying this solution to the manufacture of magnesia and its
salts, and to the precipitation of carbonate of lead from any of the soluble
salts of lead, but particularly the chloride of lead, in which latter case the
carbonate of lead so precipitated is triturated with a solution of caustic potash
or soda, by which a small quantity of chloride of lead it always contains is
converted into hydrated oxide of lead, and the whole rendered similar in
composition to the best white lead of commerce. And in further compliance
with the said proviso, I, the said Hugh Lee Pattinson, do hereby describe the
manner in which my said Invention is to be carried into effect by the following
statement thereof (that is to say) :-
I take magnesian limestone, which is well known to be a mixture of carbonate
of lime and carbonate of magnesia, in proportions varying at different locali-
ties, and on this account I am careful to procure it from places where it is
rich in magnesia. I reduce it to powder and sift it through a sieve of forty
or fifty apertures to the linear inch. I then heat it red hot in an iron retort
or reverberatory furnace for two or three hours, when the carbonic acid being
expelled from the carbonate of magnesia, but not from the carbonate of lime,
I withdraw the whole from the retort or furnace and suffer it to cool. The
magnesia contained in the limestone is now soluble in water impregnated
with carbonic acid gas, and to dissolve it I proceed as follows:-I am
provided with an iron cylinder lined with lead, which may be of any convenient
size, say, four feet long by two feet and a half diameter. It is to be made
strong enough to resist the necessary pressure, and is to be furnished with a
safety valve and an agitator, which latter may be an axis in the centre of
the cylinder, with arms reaching nearly to the circumference, all made of iron
and covered with lead. The cylinder is placed horizontally, and one extremity
of this axis is supported within it by a proper carriage, the other extremity
being prolonged, and passing through a stuffing box at the other end of the
cylinder,so that the agitator may be turned round by its projecting end either
by hand or by machinery. A pipe leading from a force pump is connected
with the under side of the cylinder, through which carbonic acid gas may be
forced from a gasometer in communication with the pump, and a mercurial
guage is attached to shew at all times the amount of pressure within the
cylinder independently of the safety valve. Into a cylinder of the size given

page_text: I introduce from one hundred to one hundred and twenty pounds of the
calcined limestone with a quantity of pure water, nearly filling the cylinder;
I then pump in carbonic acid gas, constantly turning the agitator and forcing
in more and more gas till absorption ceases under a pressure of five atmo-
spheres. I suffer it to stand in this condition three or four hours, when I run
off the contents of the cylinder into a cistern and allow it to settle. The
clear liquor is now a solution of carbonate of magnesia in water impregnated
with carbonic acid gas, or, as I shall hereafter call it, a solution of bicarbonate
of magnesia, having a specific gravity of about 10-28, and containing about
one thousand six hundred grains of carbonate of magnesia to the imperial
gallon. I consider it the best mode of obtaining a solution of bicarbonate of*
magnesia from magnesian limestone to operate upon the limestone after being.
calcined at a red heat in the way described, but the process may be varied by
using in the cylinder the mixed hydrates of lime and magnesia obtained by
completely burning magnesian limestone in a kiln as commonly practised,
and slacking it with water in the usual manner; or, to lessen the expenditure
of carbonic acid gas, the mixed hydrates may be exposed to the air a
few weeks till the lime has become less caustic by absorption of carbonic
acid from the atmosphere; or the mixed hydrates may be treated with
water, as practised by some manufacturers of Epsom salts, till the lime
is wholly or principally removed, after which the residual rough hydrate of
magnesia may be acted upon in the cylinder as described; or hydrate
of magnesia may be prepared for solution in the cylinder by dissolving mag-
nesian limestone or liydrochloric acid, and treating the solution, or a solution.
of chloride of magnesium obtained from sea water by salt makers, in the
form of bittern, with its equivalent quantity of hydrate of lime, or of the
mixed hydrates of lime and magnesia obtained by completely burning
magnesian limestone and slaking it as above. When I use this 'solution of
bicarbonate of magnesia for the purpose of preparing magnesia and its salts,
I evaporate it to dryness, by which I obtain at once a pure carbonate of
magnesia, without the necessity of using a carbonated alkali as in the old.
process, and from this I prepare pure magnesia by calcination in the usual
manner; or instead of boiling to dryness, I merely heat the solution for some
time to the boiling point, by which the excess of carbonic acid is partly driven
off, and pure carbonate of magnesia is precipitated, which I then collect and
dry in the same way as if precipitated by a carbonated alkali. If I require
sulphate of magnesia I neutralize the solution of bicarbonate of magnesia
with sulphuric acid, boil down and crystallize, or I mix the solution with
its equivalent quantity of sulphate of iron dissolved in water, heat to the
boiling point, and then suffer the precipitated carbonate of iron to subside,

page_text: after which I decant the clear solution of sulphate of magnesia, boil down,
and crystallize as before. When I use this solution of bicarbonate of
magnesia for the purpose of preparing carbonate of lead, I make a saturated
solution of chloride of lead in water, which, at the temperature of fifty or sixty
degrees Fahrenheit, has a specific gravity of about 1008, and consists of one
part chloride of lead dissolved in one hundred and twenty-six parts water. I
then mix the two solutions together, when carbonate of lead is immediately
precipitated; but in this operation I find it necessary to use certain pre-
cautions, otherwise a considerable quantity of chloride of lead is carried down
along with the carbonate. These precautions are, first, to use an excess of the
solution of magnesia, and, second, to mix the two solutions together as rapidly as
possible. As to the first, when I use a magnesian solution containing one thou-
sand six hundred grains of carbonate of magnesia per imperial gallon with a
solution of chloride of lead saturated at fifty-five or sixtydegrees Fahrenheit, one
measure of the former to eight and a half of the latter is a proper proportion, in
which case there is an excess of carbonate of magnesia employed, amounting to
about an eighth of the total quantity contained in the solution. When either
one or both the solutions vary in strength, the proportions in which they are to
be mixed must be determined by preliminary trials. It is not, however,
necessary to be very exact, provided there is always an excess of carbonate of
magnesia, amounting to from one eighth to one twelfth of the total quantity
employed. If the excess is greater than one eighth no injury will result, except
the unnecessary expenditure of the inagnesian solution. As to the second
precaution of mixing the two solutions rapidly together, it may be accomplished
variously; but I have found it a good method to run them in two streams, pro-
perly regulated in quantity, intoa small cistern, in which they are to be rapidly
blended together by brisk stirring before passing out through a hole in the
bottom into a very large cistern or tank, where the precipitate finally settles.
The precipitate thus obtained is to be collected, washed, and dried in the usual
manner. It is a carbonate of lead, very nearly pure, and suitable for most
purposes, butit always contains a small portion of chloride of lead, seldom, less
than from one to two per cent., the presence of which, even in so small a
quantity, is somewhat injurious to the colour and body of the white lead. I
decompose this chloride and convert it into a hydrated oxide of lead by
grinding the dry precipitate with a solution of caustic alkali in a mill, similar
to the ordinary mill used in grinding white lead with oil, adding just so much
of the ley as may be required to convert the precipitate into a soft paste. I
allow this paste to lay a few days, after which the chloride of lead being
entirely or almost entirely decomposed, I wash out the alkaline chloride formed
by the reaction, and obtain a white lead, similar in composition to the best

page_text: white lead of commerce. I prepare the caustic alkaline ley by boiling together
in a leaden vessel for an hour or two, one part by weight of dry and recently.
slacked lime, two parts of crystallised carbonate of soda (which being cheaper
than carbonate of potash I prefer), and eight parts of water. The clear and
colorless caustic ley obtained after subsidence will have a specific gravity of:
about 1090, and when dra.vn off from the sediment must be kept in a close;
vessel for use.
Having thus described the nature of my Invention, and the best means of
performing the same, I would have it understood that I do not claim the pre-
paration of a solution of bicarbonate of magnesia, nor the decomposition of
chloride of magnesium by means of hydrate of lime; but 1 claim,―
First, the dissolving of magnesia out of magnesian limestone and other
earthy substances containing magnesia in a soluble form, by submitting the
same to the action of water impregnated with carbonic acid gas; and also the
dissolving of magnesia, by the same mode of operating, out of the impure
hydrate of magnesia obtained by the action of hydrate of lime on a solution
of chloride of magnesium.
Second, I claim the application of this solution of bicarbonate of magnesia
'to the manufacture of carbonate of magnesia, by which I am able to produce
this latter substance (and from it pure magnesia) without the use of a car-
bonated alkali. And I claim the application of this solution of bicarbonate of
magnesia to the manufacture of sulphate of magnesia, in the manner described.
Third, I claim the application of a solution of bicarbonate of magnesia
to the manufacture of white lead by precipitation, as described, any soluble salt
of lead being used, but chiefly the chloride of lead; and,
Fourth, I claim the application of caustic alkali to the precipitate obtained
in the latter case for the purpose of converting the small quantity of chloride
of lead in the precipitate into hydrated oxide of lead.
And I would further have it understood, that I do not confine myself to any
particular form of apparatus, provided the general character of my Invention
be retained, which is to separate magnesia from earthy substances containing
it by means of water impregnated with carbonic acid gas, and to apply the
solution of bicarbonate of magnesia thus obtained to the manufacture of
magnesia and its salts, and to the manufacture of white lead by precipitation,
in the manner already fully described.
In witness whercof, 1, the said Hugh Lee Pattinson, have hereunto set
my hand and seal, this Twenty-third day of March, in the year of our
Lord One thousand eight hundred and forty-two.
HUGH LEE (L.s.) PATTINSON.

page_text: AND BE IT REMEMBERED, that on the Twenty-third day of March, in
the year of our Lord 1842, the aforesaid Hugh Lee Pattinson, Esqre, came
before our said Lady the Queen in Her Chancery, and acknowledged the Speci-
fication aforesaid, and all and every thing therein contained and specified,
in form above written. And also the Specification aforesaid was stamped
according to the tenor of the Statute made for that purpose.
Inrolled the Twenty-fourth day of March, in the year of our Lord One