IMPROVEMENTS IN THE PRODUCTION OF CHROMIC ACID, COMPOUNDS CONTAINING CHROMIC ACID, AUDITH ARD COMBERS OF CHROMIUM
Year: 1873

page_text: LETTERS PATENT to Desmond Gerald Fitz-Gerald, of 6, Lough-
borough Road North, in the County of Surrey, Electrician, and
Bernard Charles Molloy, of 1, Elm Court, Temple, in the County
of Middlesex, Barrister-at-Law, for the Invention of "IMPROVEMENTS
IN THE PRODUCTION OF CHROMIC ACID, COMPOUNDS CONTAINING CHROMIC ACID,
AUDITH ARD COMBERS OF CHROMIUM"
ealed the 25th November 1873, and dated the 13th June 1873.
PROVISIONAL SPECIFICATION left by the said Desmond Gerald
Fitz-Gerald and Bernard Charles Molloy at the Office of the
Commisioners of Patents, with their Petition, on the 13th June
1873.
We, DESMOND GERALD FITZ-GERALD, of 6, Loughborough Road
North, in the County of Surrey, Electrician, and BERNARD CHARLES
MOLLOY, of 1, Elm Court, Temple, in the County of Middlesex, Barrister-
at-Law, do hereby declare the nature of the said Invention for "Ix-
PROVEMENTS IN THE PRODUCTION OF CHROMIC ACID, COMPOUNDS CONTAINING

page_text: of chloride of barium to one equivalent of bichromate of potash in
solution. The mixture is then boiled until the solution becomes colourless,
when pure chloride of potassium is obtained in solution, and chromate
of baryta as an insoluble powder; or two equivalents of carbonate of
baryta (which may be in the form of powdered witherite) and one
equivalent of hydrochloric acid may be added to one equivalent of
bichromate of potash in solution, the solution being boiled as before
until carbonic acid gas is no longer evolved, and the solution becomes
colourless. The chromate of baryta produced may be mixed with either
one equivalent or four equivalents of sulphuric acid (according to the
oxidizing power and the nature of the residue required), and thus used
directly as an oxidizing agent; or it may be used as a source of pure
chromic acid by adding to it one equivalent of sulphuric acid, and
separating the soluble chromic acid from the insoluble sulphate of
baryta.
In another process we add to an equivalent of bichromate of potash
in solution two equivalents of (caustic) baryta obtained from the sulphate.
of baryta by the alternate action upon this salt of reducing and oxidising
agents at a high temperature; or to one equivalent of the chromate of
potash (obtained as hercin-after mentioned) we add one equivalent of
(caustic) baryta obtained as above. In either case the products are
caustic potash (potassic hydrate) in solution, and insoluble chromate of

page_text: Lastly, we produce the chromates of lime and baryta by roasting
chalk or lime, powdered witherite or (caustic) baryta in an oxidising
flame, either with powdered chrome iron ore or preferably with sesqui-
oxide of chromium (obtained from the residues left after employing as
oxidising agents chromic acid or compounds containing it, or from
chrome iron ore by the process in which the iron in the orc is reduced
by charcoal and dissolve out by sulphuric acid, or from any other
available source), and we employ these compounds directly as oxidising
agents, or as sources of chromic acid by treating them with a mineral
acid, preferably sulphuric acid; or to obtain (basic) chromate of lead we
substitute oxide of lead for the chalk or lime, powdered withcrite or
baryta, and subsequently dissolve out the chromate of lead by means of
a caustic alkaline solution.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Desmond Gerald Fitz Gerald and Bernard Charles
Molloy in the Great Seal Patent Office on the 13th December
1873.
TO ALL TO WHOM THESE PRESENTS SHALL COME, we, DESMOND
GERALD FITZ-GERALD, of 6, Loughborough Road North, in the County
of Surrey, Electrician, and BERNARD CHARLES MOLLOY, of 1, Eleni
Court, Temple, in the County of Middlesex, Barrister-at-Law, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Thirteenth day of June, in the year
of our Lord One thousand eight hundred and seventy-three, in the thirty-
sixth year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto us, the said Desmond Gerald Fitz-Gerald and Bernard
Charles Molloy, Her special license that we, the said Desmond Gerald
Fitz-Gerald and Bernard Charles Molloy, our executors, administrators,
and assigns, or such others as we, the said Desmond Gerald Fitz-Gerald
and Bernard Charles Molloy, our exccutors, 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

page_text: of Man, an Invention for "IMPROVEMENTS IN THE PRODUCTION OF CHROMIC
AOID, COMPOUNDS CONTAINING CHROMIC ACID, AND CERTAIN OTHER COMPOUNDS OF
CHROMIUM," upon the condition (amongst others) that we, the said
Desmond Gerald Fitz-Gerald and Bernard Charles Molloy, our executors
or administrators, by an instrument in writing under our or their hands
and seals, or under the hand and seal of one of us or them, should
particularly described 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.

page_text: by concentrating the solution and adding thereto oil of vitriol in the
proportion requisite to produce a dilute sulphuric acid of specific
gravity 1.55. The chromic acid is thus precipitated, and may be
obtained in a state of purity by means which are well understood.
The potash alum obtained may, if necessary, be purified by re-crystal-
lisation or by treating its solution with a salt of baryta or of lead so as
to precipitate the chromic acid it contains; but in many cases the
presence of the latter ingredient may be regarded as advantageous.
Other methods which we adopt to obtain chromic acid from bi-
chromate of potash involve the economical production and the
decomposition by sulphuric acid of the chromate of baryta. In one
process we take about three parts of bichromate of potash and two parts
of carbonate of baryta, or witherite in fine powder, and either boil the
ingredients in water sufficient to dissolve the bichromate salt, or
intimately mix them and expose to a red heat, preferably in a closed
crucible. In this process chromate of baryta and the normal chromate
of potash (which may be separated by solution from the former salt)
are produced.
In another process we boil together or heat to redness, in a condition
of fine admixture, about 3 parts of bichromate of potash, 2 parts of
anhydrous chloride of barium (or rather less than 2 parts of the
crystallised salt) and 2 parts of carbonate of baryta or witherite, and
thus obtain chromate of baryta and chloride of potassium, which may
be separated, as in the former case.
To obtain a solution of chromic acid from the chromate of baryta
thus prepared we boil or digest 2½ parts of the salt with about 1 part
by weight of strong oil of vitriol, or to obtain an oxidizing solution
containing sufficient sulphuric acid to produce sulphate of chromium
when the solution is spent (according to the equation 2 Ba Cr О+5
H, SO, 2 Ba SO,+5 H, 0+ Cr, 3 SO.+30) we boil or digest together
equal parts by weight of chromate of baryta and strong oil of vitriol.
The solution of chromic acid is then decanted from the insoluble sulphate
of baryta. The latter, which ordinarily contains a certain proportion
of undecomposed chromate of baryta, may be utilized as a pigment by
calcining it, either per se (in which case the colour is light yellow) or in
admixture with a small proportion of charcoal or other reducing agent
(in which case the color is light green).

page_text: In another process we add to an equivalent of bichromate of potash
in solution two equivalents of (caustic) baryta obtained from the
sulphate of baryta by the alternate action upon this salt of reducing
and oxidising agents at a high temperature. Or to one equivalent of
the chromate of potash (obtained as hereinafter mentioned) we add one
equivalent of (caustic) baryta, obtained as above. In either case the
products are caustic potash (potassic hydrate) in solution and an
luble ohuomate of haruta
In another process we add to an equivalent of bichromate of potash
in solution two equivalents of (caustic) baryta obtained from the
sulphate of baryta by the alternate action upon this salt of reducing
and oxidising agents at a high temperature. Or to one equivalent of
the chromate of potash (obtained as hereinafter mentioned) we add one
equivalent of (caustic) baryta, obtained as above. In either case the
products are caustic potash (potassic hydrate) in solution and an
insoluble chromate of baryta.
To obtain chromic acid the latter is treated as in the former case, and
the sulphate of baryta produced is converted into baryta, as above.
mentioned.
Under certain conditions we manufacture chromate of lime from
commercial bichromate of potash with the object of producing an
oxidising compound (containing free or virtually free chromic acid) by
the addition of sulphuric acid to the lime salt. This oxidizing
compound when " spent" (i. e. when its available oxygen has been
utilized) consists of sesqui-oxide or sulphate of chromium and insoluble
sulphate of lime.
One method of thus obtaining the chromate of lime is to add about
1 part of slacked lime to 4 parts of bichromate of potash in saturated
solution; the sparingly soluble chromate of lime is precipitated, whilst
a mixture of the normal chromate of potash and chromate of lime is
obtained in solution. The reaction may if preferred be effected by a
furnace operation, in which case an equivalent (or 1½ parts) of car-
bonate of lime may be substituted for the caustic lime, the two
ingredients being brought into intimate admixture exposed to a red heat
and treated with sufficient water to dissolve out the chromate of potash.
The latter salt as obtained in either of these processes may be purified
by the addition of carbonate of potash in quantity sufficient to pre-
cipitate as carbonate the whole of the lime in solution.
Another method we adopt is to add to 3 parts of bichromate of potash
1 of carbonate of lime (or rather more than 1 part of quicklime, which
should be slacked before use) and 1 of chloride of calcium. In this case
chromate of lime and chloride of potassium are obtained, the latter salt
being purified by digestion with sulphate of lead in sufficient quantity
to decompose the chromate of lime in solution,

page_text: t
Another method is to add to 5 parts of bichromate of potash 1 part of
quicklime (which should be slacked before use), and 2½ parts of
sulphate of lime. In this case chromate of lime and sulphate of potash
are obtained, the latter salt being purified by digestion with sulphate of
lead (forming a yellow pigment) as in the preceding instance. These
two reactions, like the first, may be effected either in the moist way or by
a furnace operation. We prefer however to obtain chromate of lime (to
be used in this case either as an oxidant, being then in admixture with a
mineral acid, or for obtaining other compounds of chromuim) directly
from chrome iron ore, by roasting or heating in a reverberatory furnace
traversed by a current of air, and intimate mixture, about 10% cwt.
of chalk (for which an equivalent of lime may, if preferred, be
substituted), and one ton of chrome iron ore, both in fine powder, the mass
being afterwards lixiviated or ground with water. Chromate of lime is
by similar processes formed in many chrome works as a preliminary stage
in the manufacture of bichromate of potash being decomposed whilst yet
in solution by the addition of carbonate of potash; or according to
Jaquelain's process it is converted by means of sulphuric acid into
bichromate of lime (di-hydro-chromate of lime, Ca H, 2 Cr O₂) which
to obtain bichromate of potash is decomposed whilst yet in solution by
carbonate of potash. Instead of so decomposing the bichromate of lime
we add to its solution slacked lime until the fluid gives an alkaline
reaction, and we then separate the precipitated chromate of lime from
that which is held in solution, and obtain the salt in an isolated form by
drying the former in a current of air or otherwise, and by evaporating
the solution to dryness. Or to the solution of bichromate of lime we
add sulphuric acid or other mineral acid (preferably in the proportions
of 1 equivalent, or of 4 equivalents to the equivalent of bichromate of
lime) and use the mixture as an oxidising agent, which when "spent"
consists of a salt of lime and sesqui-oxide of chromium, or of a salt of
lime and a salt of chromium (according to the proportion of acid used).
Or instead of decomposing by carbonate of potash or sulphuric acid the
chromate of lime formed in the first instance we obtain it as an ultimate
product, or in a separate and isolated form by simply allowing the fluid
product of the lixiviation of the roasted mixture of chalk (or lime) to a
deposit impurities by subsidence, and afterwards evaporating to dryness
the clear solution.
To extract the salt in the first instoren na hinhuomata

page_text: the proportion of 1 equivalent for every 2 equivalents of chromate of
lime contained in the quantity of the mixture operated upon.
4
4
In using chromate of lime by whatever process it may be obtained to
produce an oxidising mixture which, when "spent," consists of a salt of
5 lime and sesqui-oxide of chromium, we prefer to add sulphuric acid in
the proportion of one equivalent to each equivalent of chromate of lime,
that is to say, about 2 parts of strong oil of vitriol to 3 parts of chromate
of lime (according to the equation 2 Ca Cr O₁ + 2 H, S O₁ = 2 Ca S
0,+Cr. O,+2 H₂ О+3 0). But we do not confine ourselves either to
the use of sulphuric acid or to the exact proportions specified, since any
mineral acid and other proportions of acid may in some cases be equally
effective. And in using chromate of lime by whatever process it may
be obtained to form an oxidising mixture which when "spent” shall
consist of a salt of lime and a salt of chromium, we prefer to add to it
5 sulphuric acid in the proportion of 5 equivalents to every 2 equivalents
of chromate of lime, that is to say, in the proportion of about 5 parts of
sulphuric acid to 3 parts of chromate of lime (according to the equation
2 Ca Cr O + 5 H₂ S O₁ = 2 Ca S O₁ + Cr, 3 S O̟ + 5 H₂ O +3 O).
But in this case also we do not confine ourselves either to the use of
sulphuric acid or to the exact proportions specified.
We would have it clearly understood that we do not claim the process
by which chromate of lime is formed since the salt has been frequently
so formed as an intermediate stage in the manufacture of bichromate of
potash. What we claim is,―
1. The production of crude chromic acid or of oxidising solutions
containing free chromic acid by means of the addition to a solution of
bichromate of potash of sulphate of alumina, and of sulphuric acid, as
hercin-before particularly described.
2. The particular modes of obtaining chromate of baryta, and the use
as an oxidising agent of the fluid obtained by treating this salt with
sulphuric acid in the proportion requisite to produce a salt of chromium,
as herein-before described.
3. The use as oxidising agents of mixtures of chromate or of bichromate
of lime and sulphuric acid, or other mineral acids, as hercin-before
particularly described.

page_text: 4. The production of chromate of lime by the addition of lime or
hydrate of lime to solutions of bichromate (di-hydro-chromate) of lime, as
herein-before described.
5. The production in a separate and solid form of chromate of lime
obtained directly from chrome iron ore, as herein-before described.
In witness whereof, I, the said Desmond Gerald Fitz-Gerald,
have hereunto set my hand and seal, this 12th day of December,
in the year of our Lord One thousand eight hundred and seventy-
three.
DESMOND G. FITZ-GERALD. (L.S.)