Improvements in the Manufacture of Venetian Red.
Year: 1891

page_text: Date of Application n
Complete Specification Left, 5th Dec., 1891-Accepted, 6th Feb., 1892
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Venetian Red.
I, WALTER JOHN WIGG, of Frodsham, in the County of Chester, Colour
Manufacturer, 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 :-
Hitherto, when it has been desired to obtain Venetian red, the coloring oxides
of iron have been first produced or obtained in any suitable way (as for instance by
the process of Letters Patent No. 370,511, granted in the United States of America
September 27th, 1887, to Wigg, Steele and Wigg) and have then been mechanically
mixed in a dry powdery state with powdered barytes, gypsum, or the like body-
forming agents ("as for instance by the process of the Peterson United States
Patent No. 203,936, dated May 21, 1878 "). In effecting this mechanical admixture
expense and time are involved, and in the end even at the best the two ingredients,
the coloring agent and the body-forming, that is the color-reducing agent, are in
separate particles of greater or less size and irregularly intermingled, and the
quality of the color is irregular and inferior.
The object of my invention is to obviate the above disadvantages and to obtain
cheaply and directly and in one operation Venetian red of good color and body;
and it consists in the processes herein described and claimed.
In carrying out my invention I preferably begin with the residual copper liquor
obtained in the precipitation of copper by the wet process, although any liquor will
answer which contains in solution a sufficient proportion of a salt of iron to make it
worth while treating it, and which contains also in solution (in the same or in a
different salt) a suitable proportion of a substance which will, on the admixture of
the re-agent employed, form with that re-agent or with its base an insoluble salt or
substance suitable for a body-forming or color-reducing substance. The residual
copper liquor referred to and preferred may be generally stated as containing in
solution about ten per cent. of chloride of iron, and sixteen per cent. of sulphate of
soda the substances specially operative in my process-and with them three per
cent. of chloride of sodium, traces of other salts, and seventy one per cent. of water,
though said proportions, will, of course vary considerably.
This liquor, thus containing soluble iron and a suitable proportion of another
suitable soluble substance as described, I treat with a large excess of milk of lime,
milk of magnesia, or the like suitable oxide-this reagent being in sufficient excess
to accomplish the following results :-namely, approximately all the iron of the
soluble salt of iron in the liquor becomes more or less oxidized and insoluble and
substantially all the other soluble salt or substance of the liquor unites with the
reagent or with its base, forming also an insoluble salt in quantity in excess of the
insoluble oxide of iron produced, the whole compound precipitate being of a greenish
color. The relative proportions of the residual copper or other liquor and the milk
of lime that I find satisfactory in practice are about six hundred weight of the lime
to such a quantity of the residual copper or other liquor employed as will produce

page_text: about a ton of Venetian red. Care must be taken to employ much more of the
milk of lime than would simply be an equivalent of lime for the purpose of
precipitating the iron as an oxide, for the other soluble salt or substance of the
liquor appropriates and requires more of the reagent even than does the iron. The
mixture is preferably kept agitated for several hours, and preferably, with the first
beginning of the mixing, I begin to oxidize the product by forcing air or other
oxidizing gas or agent through the mixture. This is kept up for several hours and
it acts both to thoroughly agitate and intermingle the green colored mixture and
also to further oxidize it, causing it to gradually assume a yellow or yellowish-red
color.
This air-oxidizing step is preferably followed and supplemented by a steam
cxidizing and cleansing step; or the precipitate, after the mother liquor is drawn
off, is washed with water; or both steam and water are used. Then the washed
precipitate is preferably filtered in filter presses and then it is in all cases furnaced
in the usual way.
I show in the drawings apparatus well adapted to carry out my new process in its
preferred form, and I will now proceed to describe that preferred process more in
detail in connection with the said drawings.
a is the mixing and oxidizing vessel. It may be built for instance some 30 feet
in height and 10 or 12 feet in diameter, and is preferably cylindrical. Into this
mixing and oxidizing chamber is pumped the residual copper liquor or other liquor
employed, and at the same time and at a proper relative rate is pumped the milk
of lime, this through pipes shown in the drawings. When the mixture has attained
a depth of three or four feet in the vessel a air is turned on through the pipe b and
is forced up out of the perforated-arms of the pipe at the bottom of the vessel a
through the mixture. Thus is kept up a violent and continuous agitation of the
liquid contents of the vessel a. It will ordinarily take an hour or two to fill the
tank a with the copper liquor and the milk of lime or other reagent employed.
During all this time the blast of air has been kept up and it is preferably kept up
for some two hours or more after the vessel a is full. Owing to the continuous
violent agitation of the liquid the vessel a should not be filled to the top. The
time of shutting off the air blast is determined however by the condition and color
of the mixed liquor the air blast being continued until the whole of the precipitate
is of a yellowish red color. The milk of lime is preferably shut off when a small
amount of the dissolved iron is still unprecipitated. The mixture which has now
somewhat of a yellow or yellowish red color, is allowed to run out into the steam
washing and oxidizing vessel c, where it is submitted to the action of steam
introduced through the pipe d which has perforations at the bottom of the vessel as
shown.
From this vessel c the mother liquor is drawn off, the insoluble ingredients of the
mixture being allowed to settle to the bottom of the vessel. Pure water also is
introduced from time to time and drawn off, the insoluble precipitate being thereby
and by the action of the steam cleansed from soluble ingredients. The steam also
operates upon the precipitate apparently to further oxidize it and the color is
slightly deepened.
The apparatus e represents diagrammatically an ordinary filter press, where the
large excess of moisture is squeezed out from the precipitate and from which the
precipitate in cakes is introduced into the revolving cylindrical furnace f. This
furnace revolves about once in four minutes. The precipitate is being continuously
introduced at the upper end and the furnaced product, now a brilliant red, is
continuously delivered at the lower and opposite end of the furnace.
The heat is derived from the fire place g, the products of combustion from which
pass through the furnace f in contact with the precipitate and out through a suitable
vent at the other end of the furnace.
Air is introduced into and above the fire g, so that that the character and
quality of the flame in the furnace is readily controllable. Ordinarily the
furnacing consumes about an hour from the time a given mass of material enters

page_text: the furnace until it leaves it. The parts are preferably arranged as shown in the
drawings, one above the other, so that the treated material can be passed by
gravitation from one vessel to another, or when necessary pumps and elevators may
be used to raise the materials from one vessel to another.
It will be observed that by my improved process, the combination of the color-
producing oxide of iron with the body-forming or color-reducing substance (which
combination constitutes the Venetian red-the ultimate product sought) is effected,
not mechanically, as a mere mechanical admixture of dry powdered materials, but
is effected primarily and, as it were, chemically, the two substances being precipitated
simultaneously from the same solution; and it will also be observed that the thing
subjected to the furnacing step of the process is, not the color-producing substance
(the oxide of iron) but it is the combination substance consisting of the color-
producing material and in greater excess the body-forming or color-reducing
material.
The Venetian red produced by my process is therefore superior to that heretofore
produced or possible to be produced.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The process of producing Venetian red which consists in treating a proper
solution of iron and of a body-producing substance, with milk of lime or equivalent
reagent and furnacing the precipitate, substantially as and for the purpose
described.
2. The process of producing Venetian red which consists in treating a proper
solution of iron and of a body-producing substance, with milk of lime or equivalent
reagent oxidising the mixture and then furnacing the precipitate, substantially as
and for the purposes described.
3. The process of producing Venetian red, which consists in treating residual
copper liquor (obtained in the precipitation of copper by the wet process) with an
excess of milk of lime or equivalent reagent, oxidizing the mixture, and then
furnacing the precipitate, substantially as and for the purposes described.
4. The process of producing Venetian red which consists in treating a proper
solution of iron and of a body-producing substance, with milk of lime or equivalent
reagent agitating and oxidizing the mixture by blowing air or other oxidizing gas
or agent through it, further oxidizing and cleansing the precipitate by steam and
water, and then furnacing the precipitate substantially as and for the purposes set
forth.
Dated this 4th day of December 1891.