IMPROVEMENTS IN THE MANUFACTURE OF ARSENIOUS ACID AND METALLIC ARSENIC
Year: 1876

page_text: LETTERS PATENT to Edward Androw Parnell, of Swansea, in the County of
Glamorgan, Chemical Manufacturer, for the Invention of "IMPROVEMENTS IN
THE MANUFACTURE OF ARSENIOUS ACID AND METALLIC ARSENIC."
COMPLETE SPECIFICATION filed by the said Edward Andrew Parnell at the
Office of the Commissioners of Patents on the 12th May 1876.
EDWARD ANDREW PARNELL, of Swansea, in the County of Glamorgan, Chemical
Manufacturer. "IMPROVEMENTS IN THE MANUFACTURE OF ARSENIOUS ACID AND
METALLIC ARSENIC."
My said Invention relates to certain methods of extracting arsenic from the
arsenical bye-product obtained in the preparation of colouring materials by the action
of arsenic acid on aniline or other similar substances. The said bye-product consists
for the most part of a compound of arsenious acid and lime, and it also contains
carbonaceous matters derived from the aniline or other similar substances. When
the said arsenical bye-product is calcined at a moderate heat, a portion of its arsenic,
amounting to about one-third of the total quantity present, is disengaged and
volatized as metallic arsenic. The remainder of the arsenic is contained in the
residue in the state of arseniate of lime, from which heat alone is insufficient for
the elimination of the arsenic.
Under my said Invention the decomposition of the arsenical lime compound is
effected by the addition of a siliceous material in conjunction with a carbonaceous
or other deoxidizing material. At a moderate red heat the lime then unites with
silica, thereby producing silicate of lime, and the arsenic is disengaged in the
metallic state and capable of being condensed and collected in the usual way in a
condenser or long flue. The presence of a deoxidizing agent in conjunction with
silica is essential to effect a rapid decomposition of the arsenical lime compound.
The said process may be conducted successfully in a variety of ways; for
example, the arsenical bye-product may be mixed in a direct manner without
previous calcination with the siliceous material, or it may be first calcined, and
the resulting arseniate of lime mixed with silica and a deoxidizing substance. In
the raw or uncalcined state the said bye-product often contains sufficient carbona-
ceous matter to render the further addition of reducing material unnecessary.

page_text: In carrying out my said Invention I do not confine myself to the use of carbona-
ceous material as a reducing agent, as arsenical pyrites or inundic may likewise be
employed with good results. The arsenic contained therein, as well as that in the
lime compound is disengaged, and a mixture of silicate of lime and silicate of oxide
of iron remains behind.
Of the materials before-mentioned the proportions which I prefer to employ are
the following:
1. With siliceous sand and coal. To a quantity of the uncalcined arsenical bye-
product containing four parts of lime (as found by previous analysis) I add five parts
of fine siliceous sand, mix the same intimately, and afterwards add two parts of
small coal; or if the arsenical bye-product has been previously calcined I mix
together about ten parts of the arseniate of lime, six parts of fine siliceous sand,
and six parts of small coal.
2. With arsenical pyrites mixed with quartz or sand. As arsenical pyrites is
always found in nature associated with more or less quartz, I select such ore of
inferior quality as contains about two-thirds of its weight of quartz, and one-third
of mispickle, corresponding to about 15 per cent. of metallic arsenic. Such ore is
crushed and reduced to a state of fine powder, and I mix ten parts thereof with a
quantity of the uncalcined arsenical bye-product which is found by analysis to
contain three parts of lime; or I mix ten parts of such ore as last-mentioned with
six parts of the calcined arseniate of lime.
The heating of these several mixtures may be effected either in a close furnace
or in an open reverberatory furnace. When the latter kind of furnace is employed
it should be constructed with returning flues under the working bed, and openings
should be made in the end of the furnace for the admission of air, so that the
arsenic may become oxidized and pass into the condensing chamber as arsenious
ncid.
For the purpose of heating the mixture of the uncalcined arsenical bye-product
with sand I prefer to employ a revolving cylinder similar to what is known as
"Oxland and Hocking's," revolving calciner for ores and minerals, the same being
slightly inclined with a fire-place at one end. The raw mixture is allowed to enter
continuously in a dry state into the cylinder at the end farthest from the fire,
and the silicate of lime to flow out in a pulverulent state from the end next the
fire. If the raw materials have been well mixed it is not necessary that the heat
be raised so high as to cause incipient fusion of the silicate of lime.
The most convenient source of heat, whether the furnace be a reverberatory
furnace or a revolving cylinder, is a "gas producer" similar to that employed in
connection with the "Siemen's regenerative furnace." By means of the gas producer
sufficient heat is obtained without exposing the mixture to excess of air. In order
to oxidize the volatilized metallic arsenic and obtain arsenious acid, air is admitted
through openings in the condensing chamber when it adjoins the revolving
cylinder.
Another method which I also employ for conducting my process is as follows:-
Having calcined the said arsenical bye-product I mix the resulting arseniate
of lime with moist clay, sand, and small coal, and form the mixture into balls or
pellets, which when dry I calcine in an ordinary kiln heated by a subjacent
reducing fire. For this mode of conducting my process I employ the following
mixture-Calcined arseniate of lime, four parts; dry sand, two parts; small coal,
one part; and moist clay sufficient to contain, if dry, one part.
When my object is to obtain metallic arsenic from either of the mixtures before-
described, I carefully avoid the admission of an excess of air, not only in the
furnace but also in the condensing chamber.
When my object is to obtain arsenious acid I allow air for the combustion of the
arsenic to be sucked in at the entrance into the condenser or under the bed of
the reverberatory furnace, as herein-before described.
Having thus declared and ascertained the nature of my said Invention, and in
what manner the same is to be performed, I would observe in conclusion that I do

page_text: not confine or restrict myself to the precise methods, arrangements, and proportions
herein-before mentioned, inasmuch as the same may in some instances be varied
without departing from or interfering with the principles upon which my said
Invention is based, but what I consider novel and original, and therefore claim as being
my said Invention is, the use conjointly of a siliceous material and a deoxidizing
agent, for the purpose of extracting arsenic and arsenious acid from the before-
mentioned arsenical bye-product, either with or without previous calcination of the
latter, substantially as herein set forth.
In witness whereof, I, the said Edward Andrew Parnell, have hereunto set
my hand and seal, this Eighth day of May, in the year of our Lord One
thousand eight hundred and seventy-six,
EDWARD ANDREW PARNELL. (L.S.)