IMPROVEMENTS IN AND RELATING TO THE MANUFACTURE OF HYPOSULPHITE OF SODA
Year: 1876

page_text: ⚫ LETTERS PATENT to Richard Powell and William Atkins, both of Liverpool,
in the County of Lancaster, for the Invention of " IMPROVEMENTS IN AND
RELATING TO THE MANUFACTURE OF HYPOSULPHITE OF SODA.”
Sealed the 13th April 1877, and dated the 11th November 1876.
PROVISIONAL SPECIFICATION left by the said Richard Powell and William
Atkins at the Office of the Commissioners of Patents on the 11th November
1876.
RICHARD POWELL and WILLIAM ATKINS, both of Liverpool, in the County of
Lancaster. "IMPROVEMENTS IN AND RELATING TO THE MANUFACTURE OF HYPO-
SULPHITE OF SODA."
We take a solution of sulphide of sodium and expose an extended surface of it
to the fumes of sulphurous acid gas. Our plan of doing this is by letting it trickle
down through a chamber or tower packed with coke or other suitable material,
through which a current of sulphurous acid is made to pass. The resulting solution
on being evaporated leaves hyposulphite of soda.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Richard Powell and William Atkins in the Great Seal Patent Office
on the 25th April 1877.
RICHARD POWELL and WILLIAM ATKINS, both of Liverpool, in the County of
Lancaster. "IMPROVEMENTS IN AND RELATING TO THE MANUFACTURE OF HYPO-
SULPHITE OF SODA."
Fig. 3, section of lixiviating vats.
In manufacturing hyposulphite of soda we first prepare the sulphide of sodium by
heating the calcined sulphate of soda (commercially salt cake) in an ordinary rever-
beratory furnace with an admixture of small coal or other carbonaceous matter, by
which means the sulphate is deoxidised and converted into sulphide of sodium,
[Price Gd.]

page_text: The sulphide of sodium is then lixiviated with hot water, and the solution exposed
to the action of sulphurous acid by running it down a tower packed with coke or
some other sufficiently porous material calculated to resist the action of acids and
alkalies.
The tower should be circular in form, from 3 to 7 feet in diameter, and from 15
to 30 feet high, according to convenience and the amount of work to be done, made
as far as possible air and water tight, and constructed of some material capable of
resisting to a sufficient extent the action of sodium sulphide, caustic alkali, sul-
phurous acid, and hyposulphite of soda, and other sulphur and soda salts incidental
to the process.
A tower made of separate pieces or staves firmly hooped together in
manner of a cask, and lined with india-rubber, is what we recommend.
Up this
tower a current of sulphurous acid is conveyed by draught, the sulphurous acid
being generated or prepared in the usual way, viz., the combustion of sulphur or
pyrites in sulphur burners or pyrites furnaces of the usual construction.
The resulting liquor is run from the bottom of the tower into vessels made of
wood, india-rubber, or other suitable material, and then the impurities being first
allowed to settle out in suitable vessels, the clear liquor is run out into india-rubber
trays, glass dishes, or other vessels constructed of material practically unaffected by
the action of hyposulphite of soda (or of any unconverted sulphide, of sodium or sul-
phurous acid), and there allowed to cool, when hyposulphite of soda is deposited in
the form of crystals.
The best mode however of thoroughly explaining the details of our Invention is
to describe the plant and process as worked in the works erected by us at Liverpool
for the purpose, and of which the accompanying Drawings are the representation.
We first prepare a caustic solution of sulphide of sodium by heating sulphate of
soda with slack or small coal and a small proportion of slacked lime in the rever-
beratory furnace A. The charge on mixing which we use for this purpose consists
of 2 cwt. of calcined sulphate of soda, 1 cwt. of small coal, and 28-lbs. of slacked
lime. These materials are first carefully mixed together, then thrown into the
furnace, and there heated and worked exactly as in the well-known process of the
soda manufacture called the black ash process until the decomposition is sufficiently
complete, which should be in about 30 minutes. The charge is then drawn in its
melted state into one of the small iron barrows or waggons known in the chemical
trade as black ash bogies, and allowed to cool.
The "black ash" thus prepared is then hoisted up to the top of the tower B, and
lixiviated in a set of 3 vats or tanks C, Figs. 2 and 3, exactly as in the well-known
soda ash process of Leblanc. These vats should be constructed of wood, and jointed
or entirely lined with india-rubber; those used by us, as shewn in the Drawings,
are each 4 feet cube, and furnished with false bottoms, from which the liquor works
up through the partitions D, E, passing thus from vat to vat in the usual way.
These vats are constructed to hold or dissolve 10 balls each.
The water used for the lixiviation should be run into the first or weaker vat at as
high a temperature as can conveniently be procured. Our method is to heat the
water in a circular vessel F, Fig. 2, by means of a steam coil, and the temperature
at which we usually run it is from 150 to 200 F., and the strong vat should be worked
off at an average specific gravity of 1.310; at this strength the liquor will acquire in
its passage through the tower a sufficiently increased specific gravity to enable the
hyposulphite of soda to be crystallized without further concentration.
Liquor delivered into the tower at 1.31 specific gravity, that is to say, marking
62 on the Twaddle glass, will, if the process be properly conducted, increase in its
specific gravity to 1.39 specific gravity (or 78 Twaddle) by the action of the tower.
This is a most important point, as it saves not only the cost and difficulty of a
separate process, but avoids to a great extent the difficulties which exist in concen-
trating the hyposulphite of soda solution, the liquor itself acting on most ordinary
metals, while any remnant of undecomposed sodium sulphide, or sulphurous acid
would almost infallibly by its action on iron or lead discolour and taint the resulting
crystals.

page_text: In working the tower the black ash solution, after being prepared as already
described, is run down the tower from the tanks or reservoirs U, the stream being
regulated by means of taps V, V, through the pipe W, passing down the draft or
exit pipe X of the tower B, while at the same time a current of sulphurous acid,
obtained in the usual way by the combustion of iron pyrites (sulphide of iron) in
the pyrites furnaces or kilns Y, is drawn up through the coke S by the draught of
the tower, where it intimately intermingles with the descending liquor. A small
slide door in the exit pipe of the tower enables the workman to see that the sul-
phurous acid is properly neutralized, and he regulates the stream accordingly, while
the current of gas entering the tower can also be regulated by the damper Z in the
burner stack.
The currents of alkaline solution running down the tower, and of sulphurous acid
*meeting it, should be so regulated as to produce hyposulphite without forming other
sulphur compounds, or allowing any of the sulphide of sodium to remain uncon-
verted. The presence of the latter salt will cause the discoloration both of the
solution and the resulting crystals, while if the quantity of sulphurous acid be in
excess, some of the higher combinations of sulphur, oxygen, and sodium are formed,
and this is the point most necessary to guard against in this part of the process.
This difficulty would, we. consider, limit the size and especially the height of the
towers.
The proper distribution both of the black ash liquor and the burner gas (sul-
phurous acid) within the tower is of great importance, lest the liquor should come
down one part of the tower undecomposed, while at another part it might be too far
acted upon. For this reason we prefer round towers, and that the exit pipe should
be taken out of the centre of the top; and as the best mode of distributing the liquor
we allow it to fall upon a tile G from such a height that the liquor splashes equally
over the surface of the coke S, Fig. 1.
The liquor on reaching the foot of the tower is delivered by an india-rubber
pipe H into a charge box J, lined with india-rubber so contrived that the resulting
solution can be run at will either into the settlers I, I, or into the well K, as may
be desired. If the liquor is properly made and of the requisite strength, it is run
into the settlers I, I, which are lined with india-rubber as being the best material
for the reasons already given, and also as being a bad conductor of heat, so that the
liquor which is delivered hot from the bottom of the tower retains its heat for a
sufficient time to allow it to be thoroughly settled from solid impurities before it
begins to crystallize. From these settlers, when sufficiently settled, it is run into
shallow india-rubber trays L, L, M, M, and there crystallized. The mother liquor is
then drawn off from the trays, and the crystals of hyposulphite of soda removed to
the drying benches to be packed for sale at P.
Should the liquor on leaving the tower not be considered in a condition to run to
the crystallizing house, it is taken down into the well K by the pipe T, from which
it is pumped up either into the concentrating pan R or to again pass through the
vats C or tower B, as may be required.
The concentrating pans R should be of earthenware, so set as to be boiled by a
steam bath; and if the manufacture is well conducted there should be very little
concentration required; but it is desirable to provide them in case at any time the
liquor should ccme down too weak. The mother liquor is also pumped up into the
concentrating pan, and when boiled down to a sufficient strength, 1.400 specific
gravity, used along with the fresh liquor from the tower.
The lixiviating or sulphurating parts of this plant would be equal to the manu-
facture of about 1,000 tons of hyposulphite of soda per annum.
The pyrites burners and crystalizing trays must of course be proportioned to the
quantity of sulphur required to be used and the amount of hyposulphite of soda to
be crystallized.
Having now particularly described our Invention, and the best modes known to
us of carrying it into effect, we wish it to be understood that we do not claim as
our discovery the know fact that a current of sulphurous acid gas will convert

page_text: solutions of sulphide of sodium, hydrate of soda, or carbonate of soda, or a mixed
solution of two or all these salts, into a solution of hyposulphite of soda; nor do we
claim any one part of our process or apparatus taken separately or used for other
purposes than for those herein described; nor the adaptation of the well-known
furnace decomposition of Leblanc, known as the black ash process; nor the use of
Leblanc's method of lixiviating; nor yet the use of india-rubber for the construction
of vessels to contain acid and alkaline liquors; but what we do claim as our Inven-
tion, and desire to protect under the herein-before in part recited Letters Patent
is,—
1st. The practical application on a manufacturing scale of the process for the
making of hyposulphite of soda, substantially as herein described.
2nd. The general arrangement of plant for the manufacture of hyposulphite of
soda, substantially as herein described and shown in the accompanying Drawings.
In witness whereof, we, the said Richard Powell and William Atkins, have
hereunto set our hands and seals, this 22nd day of March, in the year of
our Lord 1877.
Witness,
WILLIAM P. THOMPSON,
British and Foreign Patent Agent,
6, Lord Street,
Liverpool.
RICHARD POWELL. (L.S.)
WM. ATKINS.
(L.S.)