IMPROVEMENTS IN PREPARING CARBONATES OR OXIDES OF LEAD AND ZINC FOR USE AS PIGMENTS AND OTHERWISE.
Year: 1872

page_text: LETTERS PATENT to Thomas Rowan, of Glasgow, in the County of
Lanark, North Britain, Manufacturing Chemist, for the Invention
of "IMPROVEMENTS IN PREPARING CARBONATES OR OXIDES OF LEAD AND ZINC
FOR USE AS PIGMENTS AND OTHERWISE.
"
PROVISIONAL SPECIFICATION left by the said Thomas Rowan at
the Office of the Commissioners of Patents, with his Petition, on
the 15th February 1872.
I, THOMAS ROWAN, of Glasgow, in the County of Lanark, North
Britain, Manufacturing Chemist, do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN PREPARING CARBONATES OR OXIDES OF
LEAD AND ZINC FOR USE AS PIGMENTS AND OTHERWISE," to be as follows, that
is to say:-
This Invention relates to improved processes for preparing carbonates
or oxides of lead and zinc for use as pigments or otherwise.

page_text: One improvement consists in mixing a soluble salt of lead or of zinc
with an alkaline carbonate in water under pressure and aided by heat,
the pressure and corresponding temperature being increased in cach
case until double decomposition takes place, whereupon a carbonate
of the lead or zinc is precipitated in the form of an extremely fine
amorphous powder. Thus if nitrate of lead and chalk are treated in this
way, on a pressure of from 30 to 40 pounds per square inch being
attained, an instantaneous or nearly instantaneous precipitation takes
place, and a very superior white lead is produced.
The salt of lead or zinc should be slightly in excess as compared with
a chemically equivalent quantity of the carbonate. Thus for every
hundred pounds of chalk or for every hundred and ninety-seven pounds
of carbonate of baryta there should be at least two hundred and seven
pounds of lead or sixty-five pounds of zinc in the soluble metallic
salt.
The salt of lead or zinc may be obtained directly from orcs of the
metal by treating such ores in a crushed or pulverised state with a
suitable acid. Thus lead ore may be treated with nitric acid, care
being taken to saturate any free acid remaining with lead. Zinc ore
may be treated with nitric acid, care being taken to saturate any free
acid remaining by adding zinc. If zinc oxide is required to be used
as a white pigment or otherwise, it is obtainable from the carbonate by
heating the latter to drive off the carbonic acid.
The lead carbonate may be more or less heated, and with or without
access of air, whereby it will be more or less completely converted into
oxide and assume more or less of a yellow or red color.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Thomas Rowan in the Great Scal Patent Office on
the 14th August 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS 30
ROWAN, of Glasgow, in the County of Lanark, North Britain, Manu-
facturing Chemist, send grecting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fifteenth day of February, in the year of

page_text: our Lord One thousand eight hundred and seventy-two, in the thirty-fifth
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said Thomas Rowan, Her special licence that I, the
said Thomas Rowan, my exccutors, administrators, and assigns, or such
; others as I, the said Thomas Rowan, my executors, administrators, and
assigns, should at any time agree with, and no others, from time to time
and at all times thereafter during the term therein expressed, should
and lawfully might make, use, exercise, and vend, within the United
Kingdom of Great Britain and Ireland, the Channel Islands, and Isle
of Man, an Invention for "IMPROVEMENTS IN PREPARING CARBONATES OR
OXIDES OF LEAD AND ZINC FOR USE AS PIGMENTS AND OTHERWISE," upon the
condition (amongst others) that I, the said Thomas Rowan, my
executors or administrators, by an instrument in writing under my,
or their, or one of their hands and scals, should particularly describe
and ascertain the nature of the said Invention, and in what manner the
same was to be performed, and cause the same to be filed in the Great
Seal Patent Office within six calendar months next and immediately
after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Thomas Rowan, do hereby declare
the nature of my said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and by
the following statement in writing, that is to say :-
My said Invention relates to improved processes for preparing carbonates
or oxides of lead and zinc for use as pigments or otherwise.
One improvement consists in mixing a soluble salt of lead or of zinc
with an alkaline carbonate in water and in causing double decomposition
to take place under the influence of pressure aided by heat, whereupon
a carbonate of the lead or zinc is precipitated in the form of an extremely
fine amorphous powder. Thus if nitrate of lead and chalk are heated
in this way a pressure of from 30 to 40 pounds per square inch above the
atmosphere is employed and causes an instantaneous or nearly instan-
taneous precipitation, yielding a very superior white lead.
When an insoluble or nearly insoluble carbonate is used the ingredients
may be mixed together 'under atmospheric pressure in the cold or hot
state in any suitable boiler or vessel capable of safely sustaining the
pressure, and the pressure and heat may be gradually applied by admitting
steam into the boiler until the decomposition is effected.

page_text: When however a soluble carbonate is used it is not mixed with the
solution of the lead or zinc salt until the proper pressure and temperature
have been attained. also prefer to treat insoluble carbonates in the
same way. I put the solution of the soluble salt of lead or zinc into a
horizontal cylindrical boiler provided with any convenient agitator or
mixer, and I put the solution of the carbonate, or if the carbonate is
insoluble, a mixture of it with water, the carbonate being in a finely
pulverised state, into a separate vessel capable of withstanding pressure,
and placed at a higher level than the boiler. This separate vessel has
a pipe fitted with a stop valve leading from its bottom to the boiler,
and both it and the boiler are provided with valves for admitting steam.
Steam is admitted into the boiler containing the solution of the soluble
salt of lead or zinc until the necessary temperature and pressure are
attained therein, after which steam is admitted into the separate vessel
and the communication between it and the boiler is opened which causes
the carbonate to pass into the boiler. The carbonate of lead or zinc
is precipitated immediately on the matters becoming mixed, and is
allowed to settle. It is afterwards washed and dried in the ordinary
way. The salt of lead or zinc should be slightly in excess as compared
with a chemically equivalent quantity of the carbonate.
Thus for every
hundred pounds of chalk or for every hundred and ninety-seven pounds
of carbonate of baryta there should be at least two hundred and seven
pounds of lead or sixty-five pounds of zinc in the soluble metallic salt.
When a soluble carbonate is used a pressure of at least thirty pounds per
square inch above the atmosphere should be employed, whilst somewhat
higher pressures should be used in the cases of insoluble carbonates.
The salt of lead or zinc may be obtained directly from ores or oxides
of the metal by treating such ores in a crushed or pulverised state with
a suitable acid. Thus the ore or oxide may be treated with nitric acid,
care being taken to saturate with lead or zinc any free acid remaining
after all the metal of the ore or oxide is taken up. If zinc oxide is
required to be used as a white pigment or otherwise it is obtainable from
the carbonate by heating the latter to drive off the carbonic acid.
The lead carbonate may be more or less heated with or without access
of air, whereby it will be more or less completely converted into oxide
and assume more or less of a yellow or red color.
Having thus particularly described my said Invention, and the manner
of performing the same, I have to state that what I believe to be novel

page_text: and original, and claim as the Invention secured to me by the herein-
before in part recited Letters Patent is,―
1. The preparing of carbonates of lead and zinc by effecting the
double decomposition of mixtures of soluble salts of those metals with
alkaline carbonates under the influence of pressure and heat, substantially
as herein-before described.
2. The preparing of oxides of lead and zinc by heating carbonates of
those metals, such carbonates being obtained in the improved manner
herein-before described.
In witness whereof, I, the said Thomas Rowan, have hercunto set
my hand and scal, this Thirteenth day of August, in the year
of our Lord One thousand eight hundred and seventy-two.
Witness,
EDMUND HUNT,
Patent Agent,
Glasgow.
THOMAS ROWAN. (L.S.)