IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD
Year: 1840

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HUGH LEB
PATTINSON, of Benshaw Grove, near 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 Tenth day of September, in the fourth year of Her reign, did,
for Herself, Her heirs and successors, give and grant unto me, the said Flugh
Lec Pattinson, Her especial licence, full power, sole privilege and authority,
that 1, the said Hugh Lee Pattinson, my exors, admñiors, and assigns, or such
others as I, the said Hugh Lec Pattinson, my exors, adñiors, 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;" in which said Letters Patent is contained a proviso that I,
the said Hugh Lec Pattinson, 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 appear.
NOW KNOW YE, that in compliance with the said proviso, I, the
said Hugh Lee Pattinson, do declare that my Invention consists in the

page_text: application of carbonate of lime to certain salts of lead in such a manner
as to produce decomposition of the said salts of lead, and a reciprocal exchange
of acids and bases between the carbonate of lime and the salt of lead employed.
By this chemical reaction I obtain carbonate of. lead or white lead, and a solu-
tion of a salt of lime, the composition of which depends upon the particular salt
of lead made use of in the process;, and in further compliance with the said
proviso, I, the said Hugh Lee Pattinson, do hereby describe the manner in
which the said Invention is to be carried into effect, by the following statement
thereof (that-is-to-say):―
The salts of lead I employ are the chloride and the nitrate; but I will in the
first place confine my observations to the: chloride of lead; and in order to
make my processes more readily understood I will detail the chemical pheno-
mena I have observed to take place when carbonate of lime and chloride
of lead react upon each other; I will then proceed to describe the manufacture
of white lead by such chemical reaction.. I find that when equivalent
quantities of chloride of lead and carbonate of lime (which are about onc
liundred and forty parts of the former and fifty of the latter) are ground
tögetlier with the addition of water until the mass is in the form of a thin
paste, this paste after a short time shews signs of cliemical action; it-thickens
and dries, and at length becomes nearly solid. In a little time this'solid' mass
begins to deliquesce, and then resolves itself into a supernatent fluid, which is
a strong solution of chloride of calcium, and a white mass, which is a mixture
of carbonate of lead and the undecomposed chloride of lead and carbonate of
line: The solution of chloride of calcium being removed, and its place
supplied by pure water; further decomposition takes place; and by renewing
the water from day to day, and grinding occasionally the two substances
originally used, chloride of lead and carbonate of lime are almost entirely
decomposed, and'the residual mass is nearly pure carbonate of lead. This, how-
ever, takes from seven-to-fourteen days to accomplish; and even then traces of
both chloride of lead and carbonate of lime may be detected on-analyzing the
'carbonate of lead produced. I have observed that a reaction very nearly
similar both in nature and extent takes place wlien equivalent quantities of
nitrate of lead and carbonate of lime (or about one hundred and sixty-six
parts of the former and fifty of the latter) are ground together in the way
described); I have further observed, that the decomposition of both the chloride
and the nitrate of lead by carbonate of lime is much facilitated by using a
solution in water of carbonic acid gas, for carbonate of lime being soluble in
water impregnated with carbonic acid gas is presented in a form to be more
readily acted upon; and when one portion of carbonate of lime is decomposed;

page_text: the carbonic acid which dissolved it immediately takes up a fresh portion,
which is readily decomposed in the same manner. In this way the process
goes on with the same portion of carbonic acid until, all the carbonate of lime
has been made to act upon the salt, of lead, when both substances, if they
have been mixed together in exact, chemical proportions, will be completely.
decomposeil: The carbonic acid water becoming a solution of salt of lime
stronger and stronger as the operation. advances, it is better towards the end
to supply its place by a fresh portion of water impregnated with carbonic acid
gas, and this may even be repeated in order to: secure the decomposition of all
the carbonate of lime employed. The vessel in which the operation is. .per-
formed requires: to: be. agitated.
I will now proceed to explain the practical means, which I pursue in the
manufacture of white lead. I employ a mill called a flint mill, which is well
known and in constant use at potteries; this is when I am using the materials
ground in water only. It consists of a strong wooden tub hooped with iron,
the bottom of which is formed of blocks of quartz or chert .stones firmly
imbeded in cement, with their upper surfaces on the same level, so as to form
a flat bottom to the tub. Upon this is carried. round by machinery other
larger blocks of stone of the same kind, by which .any hard..and brittle
substance placed in the tub with water is continually triturated and rubbed
into the finest powder: This sort of mill I adopt because when in motion
it continually mixes and rubs together the bodies submitted to its action; but
for my purpose the moving stones need not be so heavy as those used at the
potteries because 'less grinding of, the materials.is.required. It is necessary, to
avoid in its construction the use of iron where the same may be likely to come
in contact with the substances ground in the mill. Where metallic fastenings
are necessary.within the tub they may be formed of copper. Into.a mill of
this kind, twelve feet;diameter and three feet deep, Iput.twenty-one hundred
weight of chloride of lead,; and seven and a half hundredweight of carbonate
of lime, a convenient form of which is that of the best washed chalk or
whiting; I then fill the tub with water to within fifteen inches-of its edge, set
the 'mill in motion, and, grind the materials together during four to six hours,
after which. I cease grinding, and add more water to the tub till it is nearly
full. I then suffer the, whole to stand till next morning, when I find at the
bottom of the tub a white mass, which consists of carbonate of lead,mixed
with undecomposed chloride of lead and carbonate of lime, and above this
a clear liquor, which is a strong solution of chloride of calcium nearly
free from ilead. This solution I draw off by a syphon or plug. I then.add
fresh water to the tub, as much as it will conveniently hold, and renew

page_text: the grinding for a few hours, after which the mill is stopped, and the
whole allowed to settle as before till next day. The clear solution is again
drawn off, fresh water, added, and the grinding renewed for a few hours, as
before. In this way the process is continued day after day, the clear liquor
every morning becoming a weaker solution of chloride of calcium, nearly free
from lead, until at the end of from seven to fourteen days it is nearly tasteless,
when the decomposition is judged to be completed. The white mass at the
bottom of the tub has now become a carbonate of lead, not, perhaps, entirely
It is then
but very nearly free from chloride of lead and carbonate of lime.
removed from the tub, dried, and prepared in the usual manner for the
market. I have modified this process by adding to the tub in the first instance
an excess of chloride of lead, say twenty-four hundredweight of chloride of
lead to seven and a half hundredweight of carbonate of lime, grinding and
washing in the way described until all the line is removed, which is known
by the clear liquor ceasing to taste bitter. When this is fully effected, 1
convert the excess of chloride of lead into carbonate of lead by the addition
of about four hundredweight of crystals of soda, or a proportionate quantity
of pure soda ash or carbonate of potash, purposely using the alkaline carbonate
a little in excess. The grinding is continued till all the excess of chloride of
lead is converted into carbonate of lead, after which the chloride of sodium
or chloride of potassium produced with the excess of the alkaline carbonate
are removed by washing. In this way the operation is shortened, and a purer
carbonate of lead is produced. But besides the additional expense of the
alkaline carbonate, it is attended with the disadvantages that before all the
lime can be removed by washing some of the chloride of lead is apt to be
'dissolved. In this case, however, the lead may be recovered by collecting the
latter washings, and precipitating them by any of the sulphurets of potash
or soda. When, instead of grinding the materials together with pure water,
as already detailed, I use water impregnated with carbonic acid gas, my
mode of proceeding is as follows:-I have a barrel made of lead, copper, or
wood, of convenient size, which may be, say, four feet long by two and a
half feet in diameter, strongly hooped with iron, and bound at the ends to
resist the necessary pressure. This barrel is mounted on gudgeons, upon one
of which is fixed a dead and live pulley connected by.a band with machinery,
so that the barrel can be made to revolve at pleasure. The other gudgeon
has a hole through it into the barrel, with a stopcock at the outer end beyond
the bearing part of the gudgeon, which, by means of a screw joint, can be
connected with a force pump for the purpose of forcing carbonic acid gas
juto the barrel. Such an apparatus is so common and so easily understood

page_text: that Drawings or further description will be quite unnecessary. I use this
vessel as follows:-I introduce through an opening, two or three inches
diameter, in the side of the barrel, one hundred and forty pounds of chloride
of lead and fifty pounds of carbonate of lime, and fill the barrel nearly full of
pure water, closing the side opening by means of a screw plate and leather
washer in the usual manner; I then connect the barrel with the pump already
mentioned, and force in carbonic acid gas till the water within is saturated
under a pressure of four or five atmospheres, after which I set the barrel in
motion, allowing it to make about twenty revolutions per minute. The
substances within the barrel immediately begin to react upon each other, the
carbonic acid solution dissolving the carbonate of lime, and presenting it to
the chloride of lead in a form to be immediately decomposed. This goes on
until at the expiration of three or four days the action has so far advanced
that very little of the original chloride of lead or carbonate of lime remains,
and the liquid is a strong solution of chloride of calcium. The barrel may
now be stopped, and after the insoluble mass has settled the solution of
chloride of calcium may be removed by a syphon through the side opening
of the barrel; fresh water is then to be introduced; and impregnated with
carbonic acid, the barrel set in motion for a day or two longer, at the end of
which time the decomposition is fully completed, and the carbonate of lead
produced is to be well washed and dried in the usual manner. In this mode
of operating I also occasionally use an excess of chloride of lead, to secure in
a shorter time the decomposition of all the carbonate of lime, and I after-
wards decompose the excess of chloride of lead in the grinding tub or barrel
by a carbonated alkali, used also in excess, as already detailed. When I
employ nitrate of lead I proceed exactly in the way detailed of the chloride,
whether I use the grinding tub with pure water, or water impregnated with
carbonic acid gas in the barrel, except that I always employ the exact
chemical equivalents of the two substances, that is, in the grinding tub, twenty-
four hundredweight and nine tenths of a hundredweight of nitrate of lead
with seven and a half hundredweight of carbonate of lime, and in the barrel
one hundred and sixty-six pounds of nitrate of lead with fifty pounds of
carbonate of lime, in both cases suffering the substances to react till the
decomposition is completed, after which the resulting white lead is well
washed, dried, and prepared in the usual manner for the market. I also
occasionally make a solution of carbonate of lime in water impregnated with
carbonic acid gas, and with this from a solution of chloride of lead or nitrate
of lead precipitate at once pure carbonate of lead. In this mode of operating
I make the solution of carbonate of lime in the barrel already described, and