Improvements in the Manufacture of Pigments.
Year: 1892

page_text: Date of Application, 5'h Apr., 1892-Accepted, 21st May, 1892
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Pigments.
I, GEORGE WASHINGTON SCOLLAY, a citizen of the United States, residing at
No. 100 Maiden Lane, in the City, County and State of New York, in the United
States of America, Chemist, do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
The principal object of my present invention is to change or improve the color
of iron oxides and ores, hæmatite, burnt yellow or other ochres and all analogous
materials. The following is a description of the manner in which I now prefer to
work my present invention when treating what is commonly known as blue billy, a
substance which remains in the retort when iron pyrites is decomposed in sulphuric
acid works. This description will enable others skilled in the art to apply my
invention not only to the treatment of blue billy, but also to the treatment of other
analogous materials; and not only by the use of the materials and in the manner
described, but also by the use of equivalent materials which will accomplish
substantially the same result.
The following is a description of the way in which I now prefer to converi.
blue billy into a superior red pigment.
To convert this material into ferric oxide which is a commercial red pigment, it
is necessary to combine oxygen with it. While it cannot be made to take up oxygen
directly under ordinary circumstances, it can be made to take up the requisite
amount of oxygen to convert it into a ferric oxide when in the presence of oxygen
in the nascent state. The oxygen so taken up may be appropriated entirely from
the materials used, or it may be ultimately appropriated from the air.
By preference I mix with the blue billy after it has been reduced to a fine
powder, sulphate of ammonia and raise the temperature of the vessel to a moderate
heat-say, from 500 to 600 degrees F. By this treatment the sulphate of ammonia
is decomposed. The ammonia driven off is conducted out of the retort and may be
collected in any suitable vessel. Sulphate of ferric oxide remains in the retort.
By increasing the temperature, now to a low-red heat, the sulphate of the ferric
and ferrous oxide is decomposed and Nordhausen, or fuming sulphuric acid, passes
out. of the retort and may be collected in any suitable vessel. Ferric oxide which
is a valuable red pigment remains in the retort. In this operation the iron is
first converted into a salt, by the decomposition of which the red pigment
is formed.
Blue billy may be treated with any substance containing oxygen from which it
can appropriate the required oxygen necessary to convert it into a red pigment.
In order to obtain, however, a pure article or a pure color it is necessary that tho
substance used in the treatment should either leave no residue in the retort when
the treatment is completed, or the residue left must be of a color which will not
injuriously dilute or affect the color, unless, of course, such modified color be
preferred. When sulphate of ammonia is used a moderate heat drives off the
ammonia and a higher heat drives off Nordhausen acid, leaving pure ferric oxide
behind.
The blue billy may also be treated with other substances containing oxygen.
For example, I have already obtained more or less satisfactory results by the use
of the sulphate of ferrous oxide, the sulphate of ferric oxide, oxalic acid and
sulphuric acid.
However, I have obtained the best results by using a salt. My experiments
have led me to believe that when by the influence of heat in the presence of bluo
billy the elements of the salt are separated, the acid then liberated is in a more

page_text: active and efficient condition than would be the same acid if introduced into the
charge in the form of an acid while the material of the retort is less injuriously
affected, because the acid combines with the iron oxide as fast as it is liberatel.
Besides, as heat is an important element in converting the oxide of iron into a salt, the
use of a salt which does not decompose except at a temperature at which the
acid will readily combine with the iron oxide, promotes economy and secures
improved results.
Of the several materials I have employed, I prefer at present to use the sulphate
of ammonia, because I have thereby obtained the most satisfactory results with
the least trouble and expense while, like other treating agents which converts the
blue billy into sulphate of iron, the acid element after it has parted with some of its
oxygen to the iron may be made to acquire an equivalent of oxygen from the air
and hence may be, as will be hereinafter more particularly described, used over
and over again, so that theoretically an indefinitely small quantity of sulphate of
ammonia is capable of converting an indefinitely large amount of blue billy into a
red pigment by ultimately acting merely as a vehicle to carry oxygen from the air
to the iron to reinforce and change its color.
I will now describe the second feature of my invention which relates more
particularly to the reconversion of the elements disengaged during the processes
above described in which sulphate of iron is formed back again into the treating
material.
The ammonia first discharged from the retort may be collected in a vessel in which
the Nordhausen acid is also subsequently collected or, as above explained, they may
be collected in separate vessels.
If tetroxide of nitrogen or any higher oxide of nitrogen be present in the retort
containing Nordhausen acid with air and steam, a part of its oxygen will be given
up to and go to convert the Nordhausen acid, into sulphuric acid, reducing the
nitrogen tetroxide into nitrogen trioxide, which will take an equivalent of oxygen
from the air, being thereby raised again to nitrogen tetroxide; and so on until all
the work of conversion is accomplished. In this case the nitrogen trioxide or
nitrogen tetroxide act merely as vehicles or carriers of oxygen from the air to the
sulphurous acid. The sulphuric acid thus formed will if ammonia be present
combine with the ammonia, forming sulphate of ammonia. In order to obtain the
nitrogen tetroxide or higher oxide of nitrogen necessary for this purpose, nitrate
of lead, or nitrate of iron may be employed and may be decomposed by heat in any
suitable vessel forming nitrogen trioxide and oxygen. Other materials which yield
the nitrogen tetroxide or other higher forms of nitrogen oxide, or other equivalent
carrier, may be employed for the same purpose.
The manner in which I at present prefer to work my invention when treating
blue billy may be thus described; I first introduce into a retort with the blue billy
and mix with it 25 per cent. of sulphate of ammonia and one per cent. of nitrate of
lead or nitrate of iron. The vessel is now gently heated until ammoniacal gas
censes to be driven off. This gas is discharged into a retort maintained cool,
containing another charge of blue billy ground and ready to be treated. When the
evolution of ammoniacal gas ceases, I increase the heat, bringing it up to a low-
red and permit the Nordhausen acid, with the decomposed nitrate of lead, or nitrate
of iron also to pass into the retort containing the blue billy. The conversion of
the blue billy in the first mentioned retort into venetian red is now complete. It
is removed and a new charge introduced into its place. The blue billy in the
other retort which is maintained cool, is kept preferably in a state of constant
agitation. Into this second retort air and steam are admitted and sulphate of
ammonia is formed and intimately mixed with the blue billy. Heat is now applied
to this retort, first a low heat and subsequently a high heat, as before described,
and this charge of blue billy is also converted into a red pigment. The distillates
in this case, are led back into the first retort where they are mixed with a new
charge. A convenient apparatus for carrying on this operation may consist of two
separate chambers connected by a suitable duct and carried on wheels running on

page_text: a track over a furnace (so that they may be alternately heated) and, if desired,
provided with water jackets so that the temperature of one may be quickly reduced
and kept cool while the other is heated. In such an apparatus after the blue billy,
sulphate of ammonia and nitrate of lead or nitrate of iron have been introduced
into one chamber and a charge of blue billy in the other, it is only necessary to
heat the first until conversion is complete when the apparatus may be slid forward,
carrying one chamber away from the fire and bringing the other chamber over it,
when the charge from the first chamber may be removed and a new charge
introduced, and the action repeated again and again.
I desire to remark that in the foregoing Specification I have described the actions
and re-actions and the changes affected as I now understand them, but it is to be
understood that I do not limit my invention to a process or processes in which the
re-actions or changes described take place, as the effects produced may be due to
other causes not now understood by me. This Specification will be read, therefore,
merely as a statement of what I now understand to be the operation involved.
Furthermore I have herein incidently referred to a few of the modifications
which may be adopted in practicing my invention and a few of the materials to
which it is applicable, and a few of the materials which may be employed as agents
therein, but I desire it to be distinctly understood that mention by me of a few
modifications or of a few equivalents is in no way intended to exclude others not
referred to, but which are within the spirit and scope of my invention, the object
of this Specification being to instruct persons skilled in the art to practice my
invention in the way at present preferred by me and to enable them to understand
its nature. Many of the details described are not essential to my several inventions
separately considered. All this will be indicated in the concluding claims, where
the omission of elements above described is intended to be a formal declaration
of the fact that such elements are not essential to the inventions severally
covered.
Having thus particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
1. The method of making pigments, consisting in subjecting iron oxide to the
action of a salt, the acid element of which in the presence of heat sufficient to
decompose said salt will combine with the iron oxide; then subjecting the same to
heat by means of which the acid liberated combines with the iron oxide to form a
corresponding salt of iron and then decomposing said salt of iron by heat.
2. The method of making pigments, consisting in subjecting iron oxide, to the
action of sulphate of ammonia and heat.
3. The method of making pigments, consisting in subjecting iron oxide in the
presence of heat to the action of a volatile substance containing oxygen, such as
sulphuric acid, combined or uncombined, which oxygen is, in the presence of heat,
liberated and appropriated by the iron oxide; and of conducting the distillate into
another chamber containing oxygen and a carrier of oxygen, such as nitrogen
tetroxide, where it acquires the oxygen given up to the iron oxide in improving or
changing its color.
4. The method of making pigments, consisting in converting iron oxide into the
sulphate of iron; decomposing said salt; combining the acid driven off with air
and water in the presence of a vehicle of oxygen, such as nitrogen tetroxide, to
form, sulphuric acid.
5. The method of making pigments, consisting in converting iron oxide into
sulphate of iron; decomposing said salt; combining the acid driven off with air
and water in the presence of a vehicle of oxygen, such as nitrogen tetroxide, in a
retort containing a charge of oxide of iron to be converted into a pigment as herein
described.
6. The method of making pigments, consisting in heating a mixture of iron
oxide and sulphate of ammonia; decomposing the sulphate of iron thus formed

page_text: and combining the acid driven off with air and water in the presence of a vehicle
of oxygen, such as nitrogen tetroxide, and therewith treating a new charge of iron
oxide to be converted into a pigment.
7. The method of making pigments, consisting in heating a mixture of iron
oxide and sulphate of ammonia; decomposing the sulphate of iron thus formed and
combining the acid and ammonia driven off with air and water in the presence of
a vehicle of oxygen such as nitrogen tetroxide, and therewith treating a new
charge of iron oxide to be converted into a pigment.
Dated this Fourth day of April 1892.
CHEESBROUGH & ROYSTON, Fels. Chart. Inst. P.A.,
15, Water Street, Liverpool, Applicant's Patent Agents.