IMPROVEMENTS IN TREATING SULPHIDE OF SODIUM AND SULPHIDE OF POTASSIUM BY CARBONIC ACID, IN ABSORBING THE RESULTING SULPHURETTED HYDROGEN, AND IN APPARATUS TO BE USED FOR THESE PURPOSES
Year: 1876

page_text: LETTERS PATENT to Walter Weldon, of Abbey Lodge, Merton, in the County
of Surrey, for the Invention of "IMPROVEMENTS IN TREATING SULPHIDE OF
SODIUM AND SULPHIDE OF POTASSIUM BY CARBONIC ACID, IN ABSORBING THE
RESULTING SULPHURETTED HYDROGEN, AND IN APPARATUS TO BE USED FOR
THESE PURPOSES
"
Sealed the 24th January 1877, and dated the 28th August 1876.
PROVISIONAL SPECIFICATION left by the said Walter Weldon at the Office
of the Commissioners of Patents on the 28th August 1876.
WALTER WELDON, of Abbey Lodge, Merton, in the County of Surrey. "IM-
PROVEMENTS IN TREATING SULPHIDE OF SODIUM AND SULPHIDE OF POTASSIUM BY
CARBONIC ACID, IN ABSORBING THE RESULTING SULPHURETTED HYDROGEN, AND IN
APPARATUS TO BE USED FOR THESE PURPOSES."
•
This Invention relates to the conversion of sulphide of sodium and sulphide of
potassium into carbonate of soda and carbonate of potash by means of gaseous
carbonic acid, and to the first part of the treatment of the resulting sulphuretted
hydrogen for the obtainment of free sulphur therefrom by the method for which
Letters Patent, numbered 2008, and dated the 31st July, 1871, have been granted
to me.
It will be convenient in what follows to speak only of sulphide of sodium and
carbonate of soda, but all that is said of these will be equally applicable to sulphide
of potassium and carbonate of potash.
In treating sulphide of sodium by carbonic acid gas in the wet way under this
Invention I partially fill with solution of the sulphide a series of vessels which I
will call "absorbers" These absorbers must be constructed of a material which is
not seriously attacked either by an alkaline sulphide or by sulphuretted hydrogen.
I prefer to construct them either of stone, or of wood lined with lead. They are
all closed vessels, perfectly gas-tight. Each of them is furnished with a mechanical-
agitator preferably so disposed as to revolve on an axis placed horizontally, and to
be capable, when the vessel is partially filled with the solution to be treated by the
carbonic acid and the agitator is put in motion, of keeping the upper part of the

page_text: vessel constantly filled with such solution in the state of fine spray. Let us suppose
a series of six such vessels, which we may call A, B, C, D, E, and F. They are so
connected one with another by suitable pipes that solution of sulphide of sodium
entering, let us say the vessel F, from a suitable reservoir which we may call G,
shall first fill F to about half its depth, shall then flow over into E and fill that
vessel to the same depth as F, shall then similarly flow over from E into D, and
afterwards from D into C, from C into B, and from B into A, until the solution of
sulphide stands at the same height in all six vessels. Into the upper part of
vessel A, at its end furthest from vessel B, a pipe enters for the admission of carbonic
acid, and there are pipes so connecting the upper part of A with the upper part
of B, the upper part of B with the upper part of C, the upper part of C with the
upper part of D, the upper part of D with the upper part of E, the upper part of E
with the upper part of F, and the upper part of F with apparatus for the absorption
of sulphuretted hydrogen, as to permit of gases passing through the whole of the
six vessels in the direction A, B, C, D, E, F, while solution of sulphide from the
reservoir G can pass through them in the direction F, E, D, C, B, A.
This disposition of apparatus is worked as follows:-The six vossels having all
been filled to a certain depth with a solution of sulphide their agitators are put in
motion and carbonic acid is made to enter into the upper part of A; there it
partially reacts on the spray of solution of sulphide which it finds in the upper part
of that vessel, so that from the upper part of A to the upper part of B there passes
a mixture of that portion of the carbonic acid which has entered A which has not
been absorbed therein with the sulphuretted hydrogen corresponding to such portion
of the carbonic acid which has entered A as has been absorbed in that vessel In B
a portion of the carbonic acid in the said mixture of gases reacts on sulphide of
sodium, so that there passes from B to Ca mixture of carbonic acid and sulphuretted
hydrogen containing more sulphuretted hydrogen and less carbonic acid than were
contained in the mixture which passed into B from A. The mixture of gases which
passos from C into D similarly contains more sulphuretted hydrogen and less
carbonic acid than the mixture entering C, and absorption of carbonic acid and
generation of sulphuretted hydrogen thus goes on in each successive vessel of the
series until, if the rate of admission of carbonic acid into A be properly regulated,
what passes off from F is nearly or quite pure sulphuretted hydrogen. When the
solution of sulphide of sodium in vessel A. is completely converted into carbonate
the liquor pipe between that vessel and B is closed by means of a cock provided for
that purpose, and the contents of vessel A are drawn off. The cock between A and B
is then opened and more solution of sulphide from the reservoir G is passed into F,
until the vessel A is refilled to the proper depth.
The sulphuretted hydrogen which passes off from the vessel F is treated for its
absorption by a mixture with water of finely divided metallic oxide in another
apparatus exactly similar to that above described. This other such apparatus may
consist of six absorbers, H, I, J, K, L, and M. The sulphuretted hydrogen must
pass through them in the direction H, I, J, K, L, M, and the mixture of metallic
oxide and water in the direction M, L, K, J, I, H. From H there will pass off a
mixture with water of either metallic sulphide only or of metallic sulphide and free
sulphur, which mixture must then be treated under my said former Invention, the
Letters Patent for which are numbered 2008, and bear date the 31st of July 1871.
The above-described method of treating solution of sulphide of sodium is best
adapted for use when the carbonic acid is employed hot or when, for any reason, the
treatment takes place at such temperature that the product is necessarily a solution
of sesquicarbonate or other carbonate of soda. When the treatment takes place in
the cold, and in such wise as to yield a precipitate of solid bicarbonate of soda, in
accordance with an Invention described in one of my other Specifications which
will be deposited at the Patent Office on the same day as this, the six absorbers, A,
B, C, D, E, F, need not be in anywise so inter-connected that solution can flow
through then or from one into another of them, but the arrangement of the pipes
for the passage of gases from one to another of them must be such that the series

page_text: may be at will either A, B, C, D, E, F, the carbonic acid entering A and the
sulphuretted hydrogen passing off from F or B, C, D, E, F, A, the carbonic acid
entering B and the sulphuretted hydrogen passing off from A or C, D, E, F, A, B,
the carbonic acid entering C and the sulphuretted hydrogen passing off from B
or D, E, F, A, B, C, the carbonic acid entering D and the sulphuretted hydrogen
passing off from C, or E, F, A, B, C, D, the carbonic acid entering E and the
sulphuretted hydrogen passing off from D, or lastly, F, A, B, C, D, E, the carbonic
acid entering F and the sulphuretted hydrogen passing off from E.
The method of working is in such case as follows:-Each of the six absorbers is
charged directly and separately with solution of sulphide of sodium, the agitators
are set in motion and carbonic acid is admitted to vessel A, the gases which pass off
from A going into B, those which pass off from B going into C, and so on in
alphabetical order, sulphuretted hydrogen finally passing off from F.
When a sufficient quantity of bicarbonate has been precipitated in vessel A the
contents of that vessel nie withdrawn, the solid bi-carbonate therein is separated
from the mother liquor, more sulphide is dissolved in that mother liquor; with
solution so formed vessel A is re-charged, and the course of the gases is then altered
to the order B, C, D, E, F, A. When enough bicarbonate has been formed in B
that vessel is emptied and re-charged, the course of the gases being then changed
to C, D, E, F, A, B From these two examples the subsequent changes of the course
of the gases will be fully understood.
This last-described arrangement of apparatus and mode of working may also be
applied to the absorption of sulphuretted hydrogen by water in which a metallic
oxide is suspended in accordance with my former Invention as aforesaid.
Whichever of the two above-described dispositions of apparatus and modes of
working be employed it will sometimes be well, instead of applying one series of
absorbers for the decomposition of the solution of sulphide of sodium and another
series of absorbers for the decomposition of the resulting sulphuretted hydrogen, to
combine the two series, as for example, by putting them in the order A, H, B, I, C,
J, D, K, E, L, F, M, in which A, B, C, D, E, F, are for the decomposition of sulphide
of sodium and H, I, J, K, L, M, for the absorption of the resulting sulphuretted
hydrogen
Some of the dispositions of apparatus and mode of working above described
are applicable also when solid sulphide of sodium is decomposed by carbonic
acid gas
In each of the vessels used for treating solution of sulphide of sodium by carbonic
acid I prefer that there should be several diaphragms descending from the top of
the vessel to within a few inches of the solution in them when at rest, the agitators
being so disposed as to work between these diaphragms,
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Walter Weldon in the Great Seal Patent Office on the 7th February
1877.
WALTER WELDON, of Abbey Lodge, Merton, in the County of Surrey. "IM-
PROVEMENTS IN TREATING SULPHIDE OF SODIUM AND SULPHIDE OF POTASSIUM BY
CARBONIC ACID, IN- ABSORBING THE RESULTING SULPHURETTED HYDROGEN, AND IN
APPARATUS TO BE USED FOR THESE PURPOSES."
This Invention relates to the methods of working and the apparatus to be
employed for the conversion of sulphide of sodium into carbonate of soda and of
sulphide of potassium into carbonate of potash by the action of carbonic acid gas
upon solution of the said sulphides, and for the first part of the treatment of the
resulting sulphuretted hydrogen for the obtainment of free sulphur therefrom by

page_text: the method for which I have received Letters Patent, numbered 2008, of the year
1871
In describing my present Invention, and the manner of performing it, it will be
convenient to speak only of sulphide of sodium and carbonate of soda; but all that
is said of these will be equally applicable to sulphide of potassium and carbonate of
potash, except that whereas I prefer to obtain the product of the treatment of
solution of sulphide of sodium by carbonic acid gas as a solid precipitate of either
bicarbonate or sesquicarbonate of soda it will usually be necessary to be content
with obtaining in the state of solution the product of the treatment by carbonic
acid of solution of sulphide of potassium by reason of the carbonates of potash
being all so much more soluble than the corresponding carbonates of soda!
"
In treating sulphide of sodium by carbonic acid gas in the wet way, by my
present Invention, I partially fill with solution of the sulphide a series of vessels,
which I call "absorbers;" they must be constructed of, or if not constructed of,
must be lined with a material which is not seriously attacked at moderate tem-
peratures either by solution of an alkaline sulphide or by sulphuretted hydrogen
They must all be closed vessels perfectly gas-tight. Each of them is furnished with
a mechanical agitator, preferably so disposed as to revolve on an axis placed
horizontally in such wise that when the agitator is in motion it shall maintain in
the upper part of the vessel a continual rain or spray of the solution with which
the vessel is charged. The number of such vessels in each series must depend
partly upon the rate at which carbonic acid is supplied thereto, and partly upon
the speed at which the agitators are worked, but six will be a convenient number
to suppose for the purpose of the present description. We may call them
A, B, C, D, E, and F, they are so connected one with another by pipes disposed to
that end that solution of sulphide of sodium entering the vessel F from a reservoir,
which may be called G, shall flow from F into E, from E into D, from D into C,
froin C into B, and from B into A until all the six vessels are filled to about half
their depth. In the upper part of vessel A, at its end farthest from vessel B, a
pipe enters for the admission of gaseous carbonic acid, and there are pipes so con-
necting the upper part of A with the upper part of B, the upper part of B with the
upper part of C, the upper part of C with the upper part of D, the upper part of D
with the upper part of E, the upper part of E with the upper part of F, and the
upper part of F with apparatus for the treatinent of sulphuretted hydrogen, as
to permit of the following mode of working -The six vessels having all been filled
to a convenient depth with solution of sulphide their agitators are put in motion,
and carbonic acid gas is made to enter into the upper part of A. It is thus brought into
contact with an enormous surface of solution of sulphide in the state of rain or spray
in the upper part of that vessel, and with the continually renewed surface of the mass
of the charge of solution in the lower part of it. These conditions secure that much
of the carbonic acid entering A shall react upon the sulphide of sodium contained
in the solution thereof with which that vessel is charged, forming carbonate of soda
and liberating an equivalent quantity of sulphuretted hydrogen. From the upper
part of A to the upper part of B there then passes that part of the carbonic acid
which has entered A, which has not reacted therein, mixed with the sulphuretted
hydrogen which has been liberated therein, as just said. In B a part of the car-
bonic acid in the said mixture of gases reacts on the sulphide of sodium in that
vessel, so that there passes from B to C a mixture of carbonic acid gas and sul-
phuretted hydrogen containing more sulphuretted hydrogen and less carbonic acid
than were contained in the mixture which passed into B from A. The mixture of
gases which passes from C into D similarly contains less carbonic acid and more
sulphuretted hydrogen than the mixture entering C, and absorption of carbonic acid
and liberation of sulphuretted hydrogen thus go on in each successive vessel of the
series until what passes off from F is nearly or quite pure sulphuretted hydrogen.
When either the whole or such proportion as may be preferred of the sulphide in A
has been transformed into carbonate the contents of that vessel are drawn off, and

page_text: more solution from the reservoir G is then passed into F until A is again filled to
the proper depth.
The sulphuretted hydrogen which passes off from the vessel F, when it is not
applied directly to the production of sulphurous acid, is treated by a mixture with
water of finely divided metallic oxide, by the former Invention to which I have
already referred A part of my present Invention consists in performing this
treatment of the sulphuretted hydrogen by similar apparatus to that which I
have above described for treatment of solution of sulphide of sodium by carbonic
acid. This second such apparatus may also consist of six absorbers H, I, J, K, L,
and M. The sulphuretted hydrogen must enter at the upper part of H, the portion
thereof which is not absorbed in H passing into I, what is not absorbed in I passing
into J, what is not absorbed in J passing into K, what is not absorbed in K passing
into L, and what is not absorbed in L passing into M, in which last vessel of the
series if the rate of entrance of carbonic acid into A, and of the consequent genera-
tion of sulphuretted hydrogen in the series A to F be properly regulated the
absorption of the sulphuretted hydrogen will become complete. The mixture of
metallic oxide and water employed to absorb the sulphuretted hydrogen will pass
through the series of vessels in the direction M, L, K, J, I, H. From H there will
be drawn off from time to time a mixture with water, sometimes of metallic
sulphide only, sometimes of metallic sulphide and free sulphur, which mixture must
then be treated by air in other apparatus under the former Invention, the Letters
Patent for which are dated the Thirty-first of July 1871, and numbered 2008, as
already aforesaid.
The above described method of treating solution of sulphide of sodium by
carbonic acid is best adapted for use when the carbonic acid has to be employed
hot, or when for any other reason the treatment takes place at such temperature or
under such other conditions that the product is wholly or for the most part in
solution when the operation is finished. When the treatment takes place in the
cold, or otherwise, under such conditions as to yeild either bicarbonate or sesqui-
carbonate in the solid state, in accordance with another Invention for which I have
received Letters Patent, numbered 3388, and dated the Twenty-eighth of August,
1876, the six absorbers need not be so inter-connected that the solution of sulphide
can flow from one into another of then, but instead of there being so inter-connected
each of them should so communicate with the reservoir G as to be capable of being
charged with solution therefrom separately and directly, and the arrangement of
the pipes for the passage of the gases instead of being such that the gases must
always take the course A, B, C, D, E, F, should preferably be such that the series
may be at will either A, B, C, D, E, F, the carbonic acid entering A and the
sulphuretted hydrogen passing off from F, or B, C, D, E, F, A, the carbonic acid
entering B and the sulphuretted hydrogen passing off from A; or C, D, E, F, A, B,
the carbonic acid entering C, and the sulphuretted hydrogen passing off from B; or
D, E, F, A, B, C, the carbonic acid entering D, and the sulphuretted hydrogen
passing off from C; or E, F, A, B, C, D, the carbonic acid entering E, and the
sulphuretted hydrogen passing off from D; or, lastly, F, A, B, C, D, E, the cai bonic
acid entering F, and the sulphuretted hydrogen passing off from E.
The method of working in such case is as follows:-Each of the six absorbers
having been charged with solution of sulphide of sodium the agitators are set in
motion and carbonic acid is sent into vessel A, the gases which pass off from A
going into B, those which pass off from B going into C, those which pass off from
Č going into D, those which pass off from D going into E, those which pass off
from E going into F, and sulphuretted hydrogen passing from F into the further
series of absorbers, in which it and metallic oxide are to react upon each other to
form metallic sulphide and water.
When the treatment of the solution in vessel A has proceeded far enough the
contents of that vessel are withdrawn, solid bicarbonate or sesquicarbonate, as the
case may be, is separated therefrom, more sulphide is dissolved in the mother liquor,
such further quantity of water being added thereto as may be necessary to com-

page_text: pensate for that removed as water of combination with the carbonate; with the
solution so for med vessel A is recharged, and the course of the gases is now altered
to the order B, C, D, E, F, A When enough bicarbonate or sesquicarbonate has
formed in B that vessel is discharged and recharged, the course of the gases being
then changed to the order C, D, E, F, A, B. From these two examples the constant
succession of changes of the course of the gases will be fully understood
This last described arrangement of apparatus and mode of working may be
adopted also for the series of absorbers for the treatment of the sulphuretted
hydrogen.
Instead of using one series of absorbers for the decomposition of the solution of
sulphide of sodium by carbonic acid, and another and distinct series of absorbers
for the decomposition of the resulting sulphuretted hydrogen by means of a metallic
oxide mixed with or suspended in water, the two series may be combined into one,
as by arranging them, for example, in the order A, H, B, I, C, J, D, K, E, L, F, M,
in which A, B, C, D, E, F, aro for the decomposition of the sulphide of sodium, and
H, I, J, K, L, M, for the decomposition of the resulting sulphuretted hydrogen.
The method of working a series of absorbers so arranged may be either of the
two methods above described.
In the accompanying Sheet of Drawings Fig 1 is an end elevation of an
absorber. The letters on it refer to the same parts as the corresponding letters on
Fig. 2.
Fig. 2 is a side elevation, partly in section, of a series of six absorbers, as
arranged for that first described of the two methods of working set forth above
A, B, C, D, E, F, are the six absorbers, one of which, A, is shown in section; G is
the reservoir for solution of sulphide of sodium; a, a, a, a, a, a, are the pipes by
which solution of sulphide of sodium passes fiom G into F, and thereafter from
absorber into absorber; b is a stop-cock on the pipe a between G and F; c is a
cock for discharging the absorber A; is the pipe by which carbonic acid cuters A,
fffff are the pipes by which carbonic acid and sulphuretted hydrogen pass
from A to B, from B to C, fiom C to D, from D to E, and from E to F, e is the
pipe by which sulphuretted hydrogen passes from F to the second series of
absorbers, not shown in Fig, 2; g is the shaft passing through all the six absorbers,
and working through suitable stuffing boxes in the ends of them, to which the
arms for agitating the contents of the absorbers are attached; h, h, h, h, h, are the
arms for agitating the contents of vessel A; and i, i, are two diaphragms for
causing the gas or gases to descend on entering the absorber, and then, after
having been driven upwards by the agitators, to descend again before leaving it.
The arrangements in the interior of all the other absorbers are the same as in A,
except that, whereas in A the pipe a, by which solution enters that vessel, is
carried upwards to the level to which solution should be charged in all the vessels,
the pipes a, by which solution enters the other vessels, need not be so carried
upwards The pipe by which solution enters A is thus carried upwards to avoid
having a cock on this pipe between A and B, and so to avoid the risk of a careless
workman, if there were such a cock, leaving it open while discharging A.
Fig. 3 is simply to show the dispositions of pipes and cocks necessary to enable a
series of six absorbers to be worked by the second method above described. It
shows in plan six absorbers, A¹, B, C, D¹, E¹, and F, for the treatment of sulphide
of sodium by carbonic acid, and, also in plan, six others, H, I, J, K, L, and M, for
the absorption of the resulting sulphuretted hydrogen. As these second six, as
shown in Fig. 3, are arranged so as to be worked in such wise that H shall always
be the first and M always the last vessel of the series, just as in the arrangement of
six vessels for treating solution of sulphide of sodium by carbonic acid, shown in
Fig. 2, A is always the first and F the last vessel of that series, and as all the
dispositions and arrangements of the series H to M, as shown in Fig. 3, are just the
same as those already described for the series A to F, as shown in Fig. 2, the part
of Fig. 3, which represents in plan the six absorbers for sulphuretted hydrogen H
to M, requires no further description. The six vessels for the treatment of

page_text: solution of sulphide of sodium by carbonic acid, A¹, B¹², C¹, D¹, E¹, F¹, Fig. 3, are
furnished with agitators and diaphragms in the same manner as the six corres-
ponding vessels A, B, C, D, E, F, Fig. 2. From the reservoir for solution of
sulphide of sodium, G, Fig. 3, a pipe a¹ communicates in each case by a shoit
branch pipe with each of the six vessels A, B, C, D¹, E¹, F¹, and upon the six
branch pipes from this pipe a¹ are six cocks b¹, b1, b¹, b¹, b¹, b¹ By opening the
cock b¹ in the branch pipe communicating with any one of the six vessels, the cocks
61 on all the other five branch pipes from the pipe a¹ being closed, that vessel,
whichever it may be, can be charged with solution of sulphide directly from the
reservoir G¹. The carbonic acid arrives by the pipe d, from which also are six
branch pipes, one to the upper part of each of the six absorbers, and on these branch
pipes are the six cocks or valves j, k, l, m, n, o. Carbonic acid can thus be made
to pass from the pipe d' into whichever of the six absorbers is required to be the
first vessel of the series by having the cock or valve between that vessel and the
pipe & open and having the cocks or valves between the pipe and all the other
vessels closed. Thus if carbonic acid is to enter A¹ and sulphuretted hydrogen to
pass off from F¹ j must be open and k, l, m, n, and o must be closed, if carbonic
acid is to enter B and sulphuretted hydiogen to pass off from A¹ & must be open
and l, m, n, o, and j, must be closed; if carbonic acid is to enter C¹ and sulphuretted
hydrogen to pass off from B¹ must be open and m, n, o, j, & k must be closed;
and so on in the other cases.
The pipe e for conveying the sulphuretted hydrogen to the second series of
absorbers also has six branch pipes, one communicating with each of the vessels
A¹, B¹, C¹, D¹, E¹, F; and upon these branch pipes between the pipe e¹ and the six
absorbers respectively are the cocks or valves v, w, x, y, z, 21. Lastly, upon the pipes
|ƒ`ƒVƒVƒVƒVƒ¹, between A¹ and B¹, B¹ and C, C and D', D¹ and E¹, E¹ and F¹,
and F and A¹ respectively, are the cocks or valves p, q, r, s, t, u. To illustrate
the manner of working these appliances we will suppose that all the vessels
A¹, B¹, C¹, D¹, E¹, F¹, are charged to a suitable depth with solution of sulphide of
sodium from the reservoir C¹, and that for the first operation the carbonic acid is
to enter the vessel D¹. To this end the cock m must be open, but n, o, J, hi, & l
must be closed, the cock or valve 7 must be closed, but s, t, u, p, and 9 must be
오
open; and the cock or valve y must be open, but x, w, v, z, & s¹ must be closed.
Mixture of carbonic acid and sulphuretted hydrogen will then pass from D¹ to E¹,
from E¹ to F¹, from F¹ to A¹, from A to B¹, and from B₁ to C₁, through the open
cocks or valves s, t, u, p, and q, in the pipes f¹³, ƒ³, ƒ¹‚ ƒ³, ƒ³, and sulphuretted
hydrogen will pass from C¹ through the open cock or valve y into the pipe c¹, and
thence into vessel H of the second series of absorbers.
" '
When the treatment of the solution in D¹ has proceeded far enough the contents
of that vessel will be withdrawn by a cock not shown in the Drawing, and D¹ will
then be recharged with fresh solution from G' by means of the cock b¹ on the
branch pipe connecting D' with the pipe a¹ The cock m must now be closed, and
the cock opened; the cock or valve ? must be opened, and s must be closed;
and the cock or valve must be closed, and x must be opened Carbonic acid will
now enter E¹ by the cock n, mixture of carbonic acid and sulphuretted hydrogen
will pass by the open cocks or valves t, u, p, q, r, in the pipes f,fƒ¹ƒƒ¹ƒ, from
E' into F, from F into A¹, from A¹ into B¹, from B¹ into C¹, and from C¹ into D¹,
and sulphuretted hydrogen will pass off from D¹ through the open cock or valve a
into the pipe el, and thence into the second series of absorbers as before. Which
cocks are to be open and which are to be closed when F¹, A¹, B¹, or C¹ is to be the
first vessel of the series will now be obvious without further explanation.
The absorbers shown on the Drawings are represented as made of cast iron.
For the series for the absorption of sulphuretted hydrogen absorbers of cast iron
may be used, without any lining; but absorbers in which solution of sulphide of
sodium is to be treated must, if made of iron, be lined inside with some material
which sulphide of sodium does not attack.
When the solution of sulphide of sodium is treated in the absorbers cold a lining

page_text: of hard pitch will answer very well;, when it is treated therein hot a lining of
lead may be used. In like manner with the inner surface of the vessels themselves
the shaft passing through absorbers in which solution of sulphide of sodium is to
be treated must be protected by a coating of pitch or other substance on which
sulphide of sodium has little or no action at the temperatures employed. The arms
for agitating must be similarly protected if they are made of iron, but they may
conveniently be made of hard wood As it is not essential that the absorbers
should be arched at their upper part, as shown in Fig 1, the absorbers themselves
may also be made of hard wood, or of slabs of any kind of stone which is not
attacked by sulphide of sodium or by carbonate of soda, under the conditions under
which either will be contained in the absorbers; the absorbers, when made of stone,
being constructed after the same manner as chlorine stills, as will be well under-
stood. Lastly, instead of being arranged all on one level, as shown in the
Drawings, the absorbers may be disposed, each at a different level from any other, in
such wise that when the contents of A have been drawn off those of B can be
completely transferred into A, and those of C be completely transferred into B,
and so on to the end of the sories, B being thus placed at a higher level than A,
Cat a higher level than B, D at a higher level than C, E at a higher level than D,
F at a higher level than E, and the reservoir G at a higher level than F. This
disposition of the absorbers will of course require a cock in each of the pipes a, by
which solution or mixture passes from one to another of them
"
Having now described and ascertained the nature of my said Invention, and the
manner in which the same is to be performed, I claim as the Invention to be
secured to me by the herein-before in part recited Letters Patent the methods of
working for effecting the decomposition of sulphide of sodium and sulphide of
potassium by carbonic acid gas in the wet way, and for the obsorption of the
resulting sulphuretted hydrogen by a metallic oxide mixed with or suspended in
water, which are above set forth, and the use for these purposes of apparatus
disposed and arranged substanially as is described in the foregoing Specification
and illustrated by the accompanying Drawings.
In witness whereof, I, the said Walter Weldon, have hereunto set my hand
and seal, this Third of February, in the year of our Lord One thousand
eight hundred and seventy-seven.
(L.S.) WALTER WELDON.