AN IMPROVED MODE OF OBTAINING CARBONATE, OF LEAD, COMMONLY CALLED WHITE LEAD
Year: 1839

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOIN
LEIGH, of Manchester, in the County of Lancaster, Surgeon, send greeting. "
WHEREAS Her present most Excellent Majesty Queen Victoria, by
Her Letters Patent under the Great Seal of Great Britain, bearing date
at Westminster, the Twenty-eighth day of February, in the second year
of Her reign, did, for Herself, Her heirs and successors, give and grant
unto me, the said John Leigh, Her especial licence, that I, the said
John Leigh, my exors, adññiors, and assigns, or such others as I, the said
John Leigh, my exors, admors, and 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 "AN IMPROVED MODE OF OBTAINING CARBONATE, OF LEAD, COMMONLY
CALLED WHITE LEAD;" in which said Letters Patent is contained a proviso
obliging me, the said John Leigh, 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 Her said Majesty's High Court of Chancery
within six calendar months next and immediately after the date of the
said recited Letters Patent, as in and by the same, reference being thereunto
aad, will more fully and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
John Leigh, do hereby declare the nature of my said Invention to consist
in manufacturing carbonate of lead, commonly called white lead, by the
decomposition of some of the compounds of lead by certain substances not
hitherto employed for that purpose, to the best of my knowledge and belief;
and in further compliance with the said proviso, I, the said John Leigh, do
hereby describe these substances and the manner in which my said Invention
is to be performed, by the following statement thereof, that is to say :-
Firstly, I take a quantity of the lead ore called galena, say eighty-nine
hundredweight reduced to moderately fine powder, and to this I add somuch
nitric acid diluted with water as shall dissolve the lead of the galena, say, one
hundred and fifty hundredweight of nitric acid of the specific gravity 1.3,
diluted with three or four times its bulk of water; by the aid of a gentle heat
the acid and galena readily act on each other, and a solution of nitrate of lead
is formed; to this solution when clear I had a concentrated solution of common
salt or chloride of sodium, so long as any precipitation of chloride of lead
takes place, then the chloride of lead having subsided and the supernatant
liquor being decanted I wash the chloride of lead with fair water, adding the
first washings to the previously decanted liquor, which will consist of a solution
of nitrate of soda, but I do not confine myself to this mode of making the
chloride of lead, as it may be made in various other ways, as, by the decompo-
sition of any of the soluble salts of lead by the soluble chlorides of other
substances, or by the action of muriatic acid or litharge, or of the same acid
on the acetate of lead, &c. To the chloride of lead, however obtained, I add a
quantity of the purified liquor prepared from the ammoniated fluid formed in
the manufacture of coal gas, and commonly called gas liquor or gas water, or
of the purified liquor obtained in the distillation of putrescent human urine, or
of the purified matters resulting from the distillation of bones or other animal
matters, and which purified liquors are thus prepared:-The ammoniated liquor
obtained during the manufacture of coal gas,and commonly called gas liquor,
is to be introduced (after any tarry matt er has been carefully separated from it
into a distillatory apparatus connected with a receiver, which should be kept
cool, a common iron waggon-shaped boiler connected with a receiver will
answer very well. A quantity of liquor is to be distilled over by a gentle heat,
somewhat below boiling, equal to a little more than one-third the quantity
of crude gas liquor introduced. By this treatment the whole of the volatile
salts contained in the gas liquor will pass over into the receiver; the receiver
will contain a moderately concentrated solution of carbonate of ammonia,
mixed with a little hydrosulphateand hydrocyanate of ammonia; should anyoil

page_text: appear in the liquid it is to be carefully removed orskimmed off. To the liquor.
must then be added some salt of lead, I prefer to use the carbonate, which
should be finely powdered and added so long as any blackness is produced.
(The sulphur is thus separated from the liquid, and the sulphuret of lead
formed may be decomposed by dilute nitric acid. When the salt of lead ceases
to be coloured by the liquid, the latter should be allowed to stand till clear, and
then decanted from the precipitate, and if not sufficiently colourless redistilled
by a gentle heat, when it will be ready for use. When any solid carbonate of
ammonia forms on the upper part or sides of the receiving vessel it should,'
after the distillation, be dissolved in the liquid portion collected, or the ammo-
niacal salt may be procured solid by the repeated distillation at a moderate
temperature of the fluid distilled from the crude gas liquor, the salt rising and
condensing in the apparatus; this should be desulphurized after the first dis-
tillation in the manner herein-before described; the solid salt mixed with a
quantity of animal charcoal may then be introduced into a proper apparatus'
and sublimed, by which means the carbonate of ammonia will be obtained very
pure, and the solution of this in water will form a fluid fit for use. When
urine is employed instead of gas liquor it should be allowed to stand for a few
days in a covered vessel, then introduced into the distillatory apparatus, and
about three parts distilled over for every ten parts of urine introduced. The
distilled portion will consist chiefly of a solution of carbonate of ammonia; a'
little carbonate of lead should be mixed with this to separate any sulphur that
may be present, and any oily matter carefully removed. The liquor being
decanted and redistilled will be fit for use. When bones or other solid animal
matters are employed they should be introduced into an iron retort connected
with a series of receivers, as is ordinarily done in the process of distilling these
matters for the manufacture of salammoniac and bone black. The products
of the distillation collected will be solid and liquid consisting of solid carbonate
of ammonia, hydrosulphate and hydrocyanate of ammonia, and much oil.
The oil should be carefully removed as completely as possible; the liquid
portion freed from sulphur as described in speaking of gas liquor, and re-
distilled till sufficiently colourless, whilst the solid portion mixed with animal
charcoal may be sublimed, then dissolved in water, and also freed from sulphur
if necessary; or it may be at once dissolved in water, freed from sulphur
by carbonate of lead, and distilled to render it colorless.
Having described the mode of preparing these ammoniacal solutions, I shall'
now proceed to state how they are to be used in the manufacture of white lead.
On the chloride of lead washed I pour any of these solutions gradually, and
with constant stirring, so long as any decomposition takes place; some effer-

page_text: vescence occurs from the escape of carbonic acid. I allow the chloride of lead
and the liquors to remain together for twenty-four or thirty-six hours, with
occasional agitation, in which time the mutual decomposition will be com-
pleted, the ammonia being converted into a muriate, and the lead into a
mixed carbonate and hydrated oxide. This operation should be conducted in
broad shallow vessels, to allow of the exposure of considerable surface. After
standing, the liquor should be decanted, and the mixed carbonate and hy-
drated oxide well washed with water, the first washings being added to the
decanted liquor. The quantity of the purified gas liquor or other ammoniacal
solutions necessary for the decomposition of a given weight of chloride of
lead will necessarily vary with the strength of those liquors, but will be easily
determined by trying the strength of the liquors by the quantity of an acid,
as the muriatic, necessary for their neutralization. This being ascertained, it
will be easy to calculate the quantity necessary for a given weight of the
chloride of lead. I find that the chloride of lead obtained from the quantity
before stated of galena and nitric acid is decomposed by the purified liquor
obtained from about seven thousand four hundred and sixty-six gallons of crude
gas liquor. After the mixed carbonate and oxide of lead, formed as above
described, has been well washed, I pass through it in any convenient apparatus
acurrent of gaseous carbonic acid, so as to convert it into a perfect carbonate
of lead, which is to be washed, dried, and ground in the manner usually prac-
tised and which is well understood. For the chloride of lead employed in the
process just described, sulphate of lead may be substituted, precisely the same
processes and operations being required. The results in this case will be
sulphate of ammonia and mixed carbonate and hydrated oxide of lead, the
latter of which is to be fully carbonated by gaseous carbonic acid; the sulphate
of lead may be formed by the mutual decomposition of acetate of lead and
the sulphate of alumina and potassa or common alum as is often practised,
or by the decomposition of any of the soluble salts of lead by the alkaline or
soluble earthy sulphates or sulphuric acid.
In my second process, instead of using the chloride or sulphate of lead,
as herein-before described, I add gradually, and with frequent agitation, a
solution of the nitrate or acetate of lead to the purified ammoniated liquors,
so long as any precipitation is produced, whereby are formed perfect car-
bonate of lead and a solution of nitrate or acetate of ammonia, the carbonate
of lead being precipitated; after the carbonate of lead has completely subsided,
the supernatant liquors should be decanted and the carbonate of lead well
washel, the first washings being added to the first decanted liquid. The
carbonate of lead must then be dried and ground in the usual manner,

page_text: The precipitation of the carbonate of lead should be conducted in a vessel
which can be closed after each addition of the solution of nitrate or acetate
of lead, and the mixture then agitated so as to prevent the escape of much
carbonic acid.
In my third process I decompose the chloride or sulphate of lead by pouring
upon it gradually, and with continued stirring, a solution of the sesquicar-
bonate or bicarbonate of ammonia, using such sisquicarbonate as is prepared
for the purposes of commerce. For every one hundred and forty parts of
chloride of lead or one hundred and fifty-two parts of sulphate of lead, I use
a solution of fifty-nine parts sesquicarbonate of ammonia or seventy-nine parts
bicarbonateof ammonia; considerable effervescence takes placeonthemixture
of the chloride or sulphate of lead with the sesquicarbonate or bicarbonate
of ammonia, and there is formed sulphate or muriate of ammonia and perfect
carbonate of lead. This process should also be conducted in a vessel that
can be closed after each addition of the materials aud during the agitation of
the mixture. It will be unnecessary to transmit gaseous carbonic acid through
the carbonate of lead formed in this case, as if properly conducted the lead
will be fully carbonated. There is nothing in these operations requiring such
a particular form of apparatus as to render its description necessary. In the
distillatory operations the stills or boilers may be of iron; the condensers and
all the other utensils required will be best of lead.
Now, whereas in these processes I do not claim the mode of decomposing
nitrate of lead by common salt, nor any particular mode of forming chloride
or sulphate of lead; nor do I claim the method of converting the mixed
carbonate and hydrated oxide of lead into perfect carbonate of lead by gaseous
carbonic acid; but I do claim the mode of making nitrate of lead from
galena and dilute nitric acid, also the mode of decomposing the chloride,
ulphate, nitrate, or acetate of lead by the purified gas liquor, or the purified
liquor from distilled urine, or the purified matters from distilled bones and
other animal substances.
I also claim the method of decomposing the sulphate or chloride of lead by
a solution of sesquicarbonate or bicarbonate of ammonia, whereby the use of
gaseous carbonic acid is rendered unnecessary; I do not claim the mode of
concentrating the gas liquor by distillation, as that has been done before; but
I claim the method of purifying it by distilling it and separating the sulphur
by means of a metallic salt, by which it is rendered fit for the manufacture
of carbonate of lead.
And such my Invention being to the best of my knowledge and belief
entirely new and never before used within that part of Her said Majesty's