IMPROVEMENTS IN THE MANUFACTURE OF CERTAIN COLORING MATTER
Year: 1880

page_text: LETTERS PATENT to Alexander Watt, of 3, York Street, Covent Garden, in the
County of Middlesex, Chemist, for an Invention of "IMPROVEMENTS IN THE
MANUFACTURE OF CERTAIN COLORING MATTER."
PROVISIONAL SPECIFICATION left by the said Alexander Watt at the Office
of the Commissioners of Patents on the 13th April 1880.
ALEXANDER WATT, of 3, York Street, Covent Garden, in the County of
Middlesex, Chemist. "IMPROVEMENTS IN THE MANUFACTURE OF CERTAIN COLORING
MATTER."
My Invention consists of certain improvements in the manufacture of red
pigments, by means of which bright and pleasing tones of red color are obtained
very economically. It is well known that in the manufacture of jewellers' rouge
the iron is sometimes precipitated in the form of a hydrated peroxide, which after
being well washed is calcined at a red heat. To obtain a useful bright red pigment
of a permanent character, and at a very low cost of manufacture, I have discovered
that by treating the hydrated peroxido of iron in certain ways hereafter described
a bright red pigment of great beauty is obtained, and the tone of color may be
regulated according to the requirements of the manufacturer. I have also observed
that under certain conditions of temperature the hydrated peroxide of iron
undergoes considerable modifications of color, and if the process be arrested
at certain stages of the operation, the resulting pigment will assume certain
tints of color which are useful in the decorative arts. In order to obtain
such variations of red color in the most economical way, I proceed as
follows-Although the bydrated peroxide of iron may be obtained by
precipitating a persalt of iron by means of caustic potash or lime, for instance, I
prefer to employ liquid ammonia for this purpose, inasmuch as it is a volatile
alkali, and may be readily recovered and used for the same purpose over and over
again, ad infinitum. To obtain the hydrated peroxide I take a solution of any
persalt of iron, and add strong liquid ammonia, stirring briskly at the time, until
all the iron is thrown down, the ammonia being added in slight excess.
The
precipitate is then placed on a strainer and the liquid is carefully collected. When
the filtration is complete I submit tho precipitate to moderate pressure, and save
the runnings as before. The hydrated peroxide is now to be placed without

page_text: previous washing in a closely covered vessel, and heated in an oven or furnace
until the mass assumes a bright red color. I have found that the presence of the
resultant salt of ammonia in solution (if the vessel be kept closely covered) while
mechanically combined with the hydrated peroxide of iron causes the ferruginous
oxide to change from its original brown color to a bright scarlet-red, the change
being due to a slight increase of temperature above the boiling point of water,
which most saline solutions are capable of attaining. I have found that when
precipitated hydrated peroxide of iron is subjected to heat in an open vessel the
characteristic red color is only partial in the mass, the upper surface retaining its
brown color, while the interior becomes changed to bright red. When the mass
has been heated to boiling a glass rod may be occasionally dipped into it, and if it
presents a red color the operation is complete and the product may be washed with
hot water and dried in the ordinary way. It is important however to save the
first washing water, since it will be impregnated with salt of ammonia. A darker
and richer tone of red may now be imparted to the pigment by heating it to a
temperature a little below red heat, while various other shades of red, or a purple
brown tone may be obtained by augmenting the temperature to cherry-redness or
even higher. A very cheap and serviceable bright red pigment may be obtained
by adding to the above specified pure peroxide of iron so obtained certain sub-
stances which, under the conditions which I will proceed to describe, have the
effect of not only cheapening the pigment, but of enhancing its brilliancy and
attractiveness. To make a cheap bright-red pigment by my process, possessing
good body, high staining power, and good covering properties, I take certain
white substances which readily combine mechanically with the peroxide of iron,
and which do not affect the permanency of the pigment as such. For this I take,
for instance, native sulphate of lime (gypsum) calcined and washed or otherwise
freed from palpable particles or sulphate of baryta in a finely divided state, and
work such substances into a pasto with water, and when in this condition I add
the red peroxide, obtained as aforesaid, in such proportions as will form in coin-
bination a bright red pigment possessing more or less "body," according to the
requirements of the market. After the said white substance has been thoroughly
incorporated with the peroxide of iron I place the resulting mass on a drying plate
or expel the water by any convenient means, and then submit the dry product to a
moderate red heat, when the compound assumes a bright red color, richer in tone
than that obtained in the first operation.
Although the properties of the white substances and peroxide of iron may be
varied according to the taste of the manufacturer I have found that for most
practical purposes two parts of sulphate of lime or barium, for instance, to ono part
peroxide of iron prepared as described yield results which are very satisfactory.
Indeed the pigment thus formned possesses so good a body that the addition of a
still larger proportion of barium or sulphate of lime or both combined may be
added to cheapen the pigment.
To recover the ammonia it is only necessary to mix the liquor filtered from the
hydrated" peroxide of iron with recently slaked lime into the form of a paste, and
then to place it in an ammonia retort and collect the ammoniacal gas in water in
the usual way. The expressed and filtered solution of ammoniacal salt inay thus
be reconverted into liquid ammonia and be reused for precipitating the persults of
iron on the same day on which it had been first employed for the same purpose,
and with the exception of a fractional loss the whole of the ammonia may be
recovered and reapplied while other details of the process are being carried on.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Watt in the Great Seal Patent Office on the 13th October
1880.
ALEXANDER WATT, of 3, York Street, Covent Garden, in the County of
Middlesex, Chemist. "IMPROVEMENTS IN THE MANUFACTURE OF CERTAIN COLORING
MATTER."
My Invention consists of certain improvements in the manufacture of red
pigments, by means of which bright and pleasing tones of red color are obtained
very economically. It is well known that in the manufacture of jewellers' rouge
the iron is sometimes precipitated in the form of a hydrated peroxide, which after
being well washed is calcined at a red heat. To obtain a useful bright red pigment
of a permanent, character, and at a very low cost of manufacture, I have discovered
that by treating the hydrated peroxide of iron in certain ways hereinafter described
a bright red pigment of great beauty is obtained, and the tone of color may be
regulated according to the requirements of the manufacturer. I have also observed
that under certain conditions of temperature the hydrated peroxide of iron
undergoes considerable modification of color; and if the process be arrested at
certain stages of the operation the resulting piginent will assume certain tints of
color which are useful in the decorative arts. In order to obtain such variations
of red color in the most economical way I proceed as follows:-Although the
hydrated peroxide of iron may be obtained by precipitating a persalt of iron by
means of caustic potash or lime, for instance, I prefer to employ liquid ammonia
for this purpose, inasmuch as it is a volatile alkali, and may be readily recovered
and used for the same purpose over and over again, ad infinitum.
To obtain the hydrated peroxide I take a solution of any persalt of iron and add
strong liquid ammonia, stirring briskly at the tine until all the iron is thrown
down, the ammonia being added in slight excess. The precipitate is then placed on
a strainer and the liquid is carefully collected, and when the filtration is complete
the hydrated peroxide is to be placed without previous washing in a closely covered
vessel, and heated in an oven or furnace until the mass assumes a bright red color,
or the precipitate may be boiled directly until the desired color is obtained. I have
found that the presence of the resultant salt of ammonium in solution (if the vessel
be kept closely covered), while mechanically combined with the hydrated peroxide
of iron, causes the ferruginous oxide to change from its original brown color to a
bright scarlet red, the change being due to a slight increase of temperature above
the boiling point of water, which most saline solutions are capable of attaining. I
have found that when precipitated hydrated peroxide of iron is subjected to heat
in an open vessel the characteristic red color is only partial in the mass, the upper
surface retaining its brown color, while the interior becomes changed to bright red,
until by evaporation the solution becomes more concentrated, the boiling being
continued with occasional stirring until the required red tint is obtained. When
the mass has been heated to boiling a glass rod may be occasionally dipped into it,
and if it presents a red color the operation is complete, and the product may be
washed with hot water and dried in the ordinary way. It is important however to
save the first washing waters, since they will be impregnated with salt of ammonium.
A darker and richer tone of red may now be imparted to the piginent by beating it
to a temperature a little below red heat, while various other shades of red, or a
purple brown tone, may be obtained by augmenting the temperature to cherry
redness, or even higher. A very cheap and serviceable bright red pigment may be
obtained by adding to the above specified pure peroxide of iron so obtained certain
substances which, under the conditions which I will proceed to describe, have the
effect not only of cheapening the pigment, but of enhancing its brilliancy and
attractiveness.
To make a cheap bright red pigment by my process possessing good body, high

page_text: staining power, and good covering properties, I take certain white substances which
readily combine mechanically with the peroxide of iron, and which do not affect
the permanency of the pigment as such. For this I take, for instance, native
sulphate of limo (gypsum), calcined and washed or otherwise freed from palpable
particles, or sulphate of baryta in a finely divided state, and work such substances
into a pasto with water; and when in this condition I add the red peroxide,
obtained as aforesaid, in such proportions as will form in combination a bright red
pigment possessing more or less "body," according to the requirements of the
market. After the said white substance has been thoroughly incorporated with the
peroxide of iron I place the resulting mass on a drying plate, or expel the water by
any convenient means, and then submit the dry product to a moderate red heat,
when the compound assumes a bright red color richer in tone than that obtained in
the first operation.
Although the proportions of the white substances and peroxide of iron may be
varied according to the taste of the manufacturer I have found that for most
practical purposes two parts of sulphate of lime or barium, or one part of each for
instance, to one part peroxide of iron prepared as described yield results which are
very satisfactory. Indeed the pigment thus formed possesses so good a body that
the addition of a still larger proportion of barium or sulphate of lime, or both
combined may be added to cheapen the pigment.
To recover the ammonia it is only necessary to mix the liquor filtered from the
hydrated peroxide of iron with recently-slaked lime into the form of a paste, and
then to place it in an ammonia retort and collect the ammoniacal gas in water in
the usual way. The expressed and filtered solution of ammoniacal salt may thus be
reconverted into liquid ammonia and be re-used for precipitating the persalts of
iron on the same day on which it had been first employed for the same purpose, and
with the exception of a fractional loss the whole of the ammonia may be recovered
and re-applied while other details of the process are being carried on.
To carry out my Invention I take any given quantity of a solution of a persalt
of iron (perchloride by preference) of the density of about 1150. To this I add
liquid ammonia until the whole of the iron is thrown down as hydrated peroxide
in the form of a semi solid mass. I allow the ammonia to be slightly in excess.
I next place the mass on a calico strainer, taking great care to save the liquor
(chloride of ammonium in solution) which passes through the strainer. Or instead
of employing the strainer the mass may be placed in a copper or other suitable
vessel and fire applied beneath until boiled, the copper being covered by means
of a lid until the boiling point is attained. At this time I raise the lid partially
so as to favor evaporation of a portion of the water (by which the strength
of the solution of chloride of ammonium is increased) and continue the boiling
with occasional stirring until the brown mass acquires a bright orange red
color. I then place the contents of the copper in a suitable vessel and allow
the color to subside. After a few hours reposo I run off the supernatant
liquor (chloride of ammonium in solution) and add fresh water (hot water by
preference) to the deposited color and stir well. The object of this process, which I
repeat as often as may be necessary, is to wash out as much of the chloride of
ammonium as possible. This solution of chloride of ammonium is carefully
preserved and may be mixed with slaked lime placed in a proper retort and
reconverted into liquid ammonia by any of the known processes. I find that by
mixing the first runnings of chloride of ammonium solution referred to with
recently slaked lime and putting the mixture in a retort, with the addition of
moderate heat, that I can recover and re-use the ammonia employed in the first
operation if necessary on the same day, whereby a great saving in the cost of the
operation is effected. The weaker washings of chloride of ammonium solution may
be strengthened by evaporation, and the last washings may be used instead of
water for the second washing in the earlier part of the washing process of
subsequent batches of color. Other persalts of iron may be used, but the perchloride
is preferred.

page_text: When the red color (pure peroxide of iron) is sufficiently washed to free it from
chloride of ammonium I place it on a drying plate heated by a suitable furnace fire,
and when dry it assumes the form of solid cakes. I now put these cakes into a
retort or other convenient vessel and apply moderate heat until a richer tone of
color is obtained, when I withdraw the charge of color and put it aside to cool.
When powdered by any of the ordinary means the color is ready for sale.
After
In order however to make a cheap but durable product for ordinary decorative
and coating or painting purposes, I find it advantageous to combine with the pure
material certain substances, which like the peroxide of iron, may be considered
imperishable or of an unalterable nature. For this purpose I take sulphate of lime
or baryta and mix either or both of these substances in suitable proportions
(according to the price which the prepared color shall realise in the market) with
the pure peroxide prepared as above described. To do this offectually I find it best
to incorporate the ingredients in a moist state, by which the white products
(sulphate of lime and baryta) become stained by the dense coloring matter.
mixing these materials carefully together into the form of a thickish paste I dry
the mass as before, and calcine the product in an iron retort, or in any other
convenient way until the desired tone of color is obtained. The resulting pigment
is a bright and lively red of great beauty. In carrying out the calcination of the
product, whether in its pure state or in combination with sulphate of lime or
baryta, care must be taken not to apply too great a heat otherwise the color will
pass from the red stage of calcination to the purple brown. A very moderate heat,
a little below rather than above red heat, gives the best results.
The Inventor having carefully tested the durability of the color produced by his
process has found that it is perfectly unalterable in all conditions of the atmosphere;
its manufacture is simple, easy, and economical, and has many advantages over
other red pigments, amongst which may be enumerated:-1st, its durability or
unchangeable character; 2, its non-poisonous properties; 3rd, its economy of
manufacture.
Having now described the naturo and particulars of my said Invention, in such
wise that the same may be readily carried into practical effect, I claim,―
The improvements in the process of manufacturing coloring matter as herein set
forth.
In witness whereof, I, the said Alexander Watt, have hereunto set my hand
and seal, this Thirteenth day of October, in the year of our Lord One
thousand eight hundred and eighty.
In presence of
WALTER A. BARLOW,
Patent Agent and Engineer,
6, St. Paul's Churchyard,
London, E.C.
ALEXANDER WATT. (L.S.)