IMPROVEMENTS IN THE MANUFACTURE OF OXIDE OF IRON SUITABLE FOR PIGMENT AND OTHER PURPOSES, AND OF HYDROCHLORIC ACID
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Edward Andrew Parnell at the
Office of the Commissioners of Patents on the 29th September 1881.
EDWARD ANDREW PARNELL, of Swansea, in the County of Glamorgan.
"IMPROVEMENTS IN THE MANUFACTURE OF OXIDE OF IRON SUITABLE FOR
PIGMENT AND OTHER PURPOSES, AND OF HYDROCHLORIC ACID."
This Invention consists in improvements which relate, in the first place, to the
production of oxide of iron from sulphates of iron (ferrous and ferric); and,
secondly, to the production of oxide of iron from the chloride of iron produced in
tin-plate works when hydrochloric acid is employed for "pickling" the iron plates
and to the recovery of hydrochloric acid therefrom.
The first part of this Invention, which relates to the production of oxide of iron
from sulphates of iron (ferrous and ferric), is as follows:-Instead of heating the
sulphate of iron alone, as commonly practised, I add to it a'small quantity of a
reducing or deoxidizing material, sufficient to reduce the sulphuric acid to
sulphurous acid and leave the oxide of iron either wholly a ferric oxide or mixed
with a lower oxide, as may be desired. By contact with a reducing or deoxidizing
agent the decomposition of the sulphate of iron is greatly facilitated; a lower
temperature suffices, and hence the operation may be casily carried on in a muffle
furnace, whereby it is under better control and oxide of the desired colour may be
obtained with greater facility.
A variety of deoxidising materials may thus be employed to assist the decom-
position of the sulphate of iron, some in the solid state, as for example iron pyrites,
coal, charcoal, and alkali-waste, and others in the gaseous state, as sulphuretted
hydrogen and carbonaceous gases.
In ordinary circumstances I prefer using either iron pyrites or charcoal, the
proportion of which I vary according to the desired colour of the oxide, as is here-
inafter described. In carrying out this Invention, I first mix the sulphate of iron
with the deoxidizing agent in a finely divided state, which may be done in a mill
when crystallized protosulphate is used; or when the solution is operated on I prefer
evaporating the liquor in a pan heated by surface heat and adding the finely
ground deoxidizing material when the liquor begins to thicken; the materials are
well stirred and the heat continued until the mixture is nearly dry, when it may

page_text: be drawn out of the furnace. If the mixture is made in a mill with crystals, it is
desirable also to dry such mixture partially before heating it in the decomposing
furnace.
The mixture is in the next place heated to dull redness, by which the sulphate
of iron is decomposed and resolved into sulphurous acid gas and peroxide of iron,
or a mixture of peroxide with more or less black oxide, according to the proportion
used of the deoxidizing material. For this operation an open furnace (as an
ordinary calcining furnace) may be used, but as a moderate heat suffices I prefer
using a muffle furnace; in the latter the operation is under better control, and the
sulphurous gas escaping from the mixture may be made available for making
sulphuric acid or for other purposes without being mixed with gases derived from
the fire-place.
The proportions of deoxidizing material which I employ are the following:—
1. In the case of iron pyrites, to obtain oxide of iron of a light red colour, that is
to say, Venetian red, I take one part of clean iron pyrites, finely ground, to about
ten parts of anhydrous ferrous sulphate or about eighteen parts of the crystallized
sulphate (common copperas). To obtain the oxide of a dark red colour (Indian
red), or of a purple colour, Í take one part of pyrites to about eight parts of dry
ferrous sulphate or fourteen parts of ordinary crystals.
2. In the case of coal or charcoal, to obtain a light red oxide I take one part of
finely ground coal or charcoal to about thirty parts of dry ferrous sulphate or
fifty five parts of ordinary crystals. To obtain a dark red or purple oxide I take
one part of coal or charcoal to about twenty parts of dry ferrous sulphate or thirty
six of crystals.
The mixture having been partially dried as before described is heated to dull
redness in a muffle furnace with well fitting doors. Abundance of sulphurous acid
is soon evolved. When this has almost ceased the charge, which-at-this.stage.may
contain some black oxide of iron, is worked with slight admixture of air until the
desired tint is obtained, when the charge is drawn ready for levigation.
I will now describe that part of my Invention which relates to the production
of oxide of iron from the waste liquor containing chloride of iron, which is
produced in tin plate works (when hydrochloric acid has been used for the purposes
of "pickling" the iron plates), and also to the formation at the same time of
hydrochloric acid. For this purpose I evaporate the said liquor to obtain the
chloride in a solid state, and this I heat moderately in contact with aqueous
vapour.
As the heat required is very moderate this operation is most conveniently done
in a muffe furnace. The steam may be introduced into the muffle from an
extraneous source, or else it may be derived from the hydrated chloride (such as is
obtained by evaporating a solution of ferrous chloride to dryness in an open pan),
the charges of chloride being so placed in the mußße that the steam from a fresh
charge shall pass over a charge undergoing decomposition. Ferrous chloride without
access of air thus leaves a residue of black oxide of iron, which by admission of
air to the muffle and stirring may be further oxidized until the desired purple
colour is obtained. Ferric chloride heated in contact with aqueous vapour leaves
a residue of peroxide of iron.
The hydrochloride acid gas which is thus formed by the decomposition of
chlorides of iron I condense with water in the usual apparatus employed for the
condensation of that acid, that is to say, pipes, stone tanks, Woulfe's bottles, and
coke-packed towers.
The liquor above referred to contains, when fresh, the iron in state of ferrous
chloride, the ferric chloride being formed when the liquor is exposed to tho air.