IMPROVEMENTS IN THE MANUFACTURE OF ARSENIC ACID, ARSENIOUS ACID, METALLIC ARSENIC, AND BINARSENIATE OF SODA
Year: 1875

page_text: LETTERS PATENT to Edward Andrew Parnell, of Swansea, in the
County of Glamorgan, Chemical Manufacturer, for the Invention of
"IMPROVEMENTS IN THE MANUFACTURE OF ARSENIC ACID, ARSENIOUS ACID,
METALLIC ARSENIC, AND BINARSENIATE OF SODA."
Sealed the 21st September 1875, and dated the 11th June 1875.
PROVISIONAL SPECIFICATION left by the said Edward Andrew Parnell
at the Office of the Commissioners of Patents, with his Petition,
on the 11th June 1875.
I, EDWARD ANDREW PARNELL, of Swansea, in the County of
Glamorgan, Chemical Manufacturer, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN THE MANUFACTURE OF ARSENIC ACID,
ABSENIOUS ACID, METALLIC ARSENIC, AND BINARSENIATE OF SODA," to be as
follows
--

page_text: arsenious acid and lime or arsenite of lime, in the second place in the
conversion by calcination of the arsenite of lime thus formed into
arseniate of lime, and in the third place in the decomposition of arseniate
of lime by means of sulphuric acid with production of sulphate of lime
and free arsenic acid. For these purposes arsenious acid, either refined
or in the crude state (obtained by the calcination of arsenical ores)
with lime in the proportion of about ten parts of arsenious acid with
four parts of lime. This mixture may be made dry, but preferably with
the addition of water, in which case the mixture is dried before
subsequent treatment. In the next place the said mixture or compound of
arsenious acid and lime is calcined in an ordinary reverberatory furnace,
which is connected with a capacious condensing flue or chamber similar
to those used for collecting arsenious acid. On the first application
of heat the combination of the arsenious acid and lime, which has
previously been only partial, becomes complete with a resulting
production of arsenite of lime. The heat is then increased to dull redness,
at which temperature the arsenite of lime is resolved into metallic
arsenic and arseniate of lime. The former immediately unites with the
oxygen of the atmosphere, thereby producing arsenious acid which
volatilizes, condenses in the flue, and is recovered in the state of refined
white arsenic. The arseniate of lime remaining in the furnace consists
in one hundred parts of forty-eight parts of lime and fifty-two parts of
arsenic acid.
The calcination may also be conducted without free access of air in a
close oven or retort. At a red heat a portion of the arsenic (about two-
fifths of the whole) is disengaged and passes off in vapour and may be
condensed in the metallic state. The residue left in the retort consists
of arseniate of lime. After the arsenite of lime has been withdrawn
from the furnace and cooled it is mixed with diluted sulphuric acid in
the proportion of one equivalent (forty-nine parts of concentrated
sulphuric acid of 1.845 spec. gr.) to each single equivalent (twenty-eight
parts) of lime contained in the arseniate as ascertained by analysis.
Complete decomposition immediately takes place, with production of
solid sulphate of lime and free arsenic acid in solution. These are
separated by filtration, and the solution of arsenic acid evaporated either
to a state of concentrated liquid or to dryness.
Instead of making use of arseniate of lime obtained by mixing
together arsenious acid and lime, arsenite of lime obtained as a bye-

page_text: product or refuse in the preparation of colouring materials may be
employed for the purposes of this Invention. Such arsenite of lime is
calcined either in a close retort or by preference in a reverberatory
furnace connected with a condensing flue. When thus heated a portion
of the arsenic present is disengaged in vapour, which with access to air
becomes arsenious acid, and the residue after exposure to a red heat
consists of arseniate of lime suitable for decomposition by sulphuric acid
and formation of arsenic acid as above described.
In order to produce binarseniate of soda one equivalent of arseniate of
lime (200 parts) is decomposed with two equivalents of sulphuric acid
(98 parts of sp. gr. 1.845) diluted with a little water, and after being
allowed to stand, one equivalent of sulphate of soda (71.5 parts) is
added; the result is solid sulphate of lime and a solution of binarseniate
of soda, which after filtration is evaporated for crystallization.
The improvement in the manufacture of arsenious acid embraced by
this Invention relates to the application of the bye-product or refuse of
colour works containing arsenite of lime. This substance is mixed with
a quantity of sulphuric acid equivalent to the lime, as ascertained by
analysis, that is to say, 49 parts of concentrated sulphuric acid to 28
parts of lime, and the mixture then dried and calcined in a reverberatory
furnace. All the arsenic present is then disengaged as arsenious acid,
which volatilizes and is condensed in the usual way.