IMPROVEMENTS IN THE MANU- FACTURE OF SODA AND CHLORINE COMPOUNDS FROM SODIUM CHLORIDE
Year: 1883

page_text: LETTERS PATENT to Eustace Carey and Ferdinand Hurter of Widnes in the
County of Lancaster for an Invention of "IMPROVEMENTS IN THE MANU-
FACTURE OF SODA AND CHLORINE COMPOUNDS FROM SODIUM CHLORIDE"
PROVISIONAL SPECIFICATION left by the said Eustace Carey and
Ferdinand Hurter at the Office of the Commissioners of Patents on the
11th December 1883.
"
EUSTACE CAREY and FERDINAND HURTER of Widnes in the County of Lancaster
IMPROVEMENTS IN THE MANUFACTURE OF SODA AND CHLORINE COMPOUNDS
FROM SODIUM CHLORIDE"
This Invention relates to the manufacture of Soda and Chlorine compounds from
Sodium Chloride and consists in firstly effecting the decomposition of Sodium
Chloride by means of Sulphuric Acid and obtaining Sodium Sulphate and
Hydrochloric Acid and then effecting the decomposition of a solution of the Sodium
Sulphate by the employment of Ammonia in conjunction with Carbonic Acid so as
to obtain Sulphate of Aminonia and Sodium Carbonates, such decomposition being.
effected in a manner similar to and in apparatus similar to that now employed
or capable of being employed in the production of Carbonate of Soda from
Chloride of Sodium by the employment of Ammonia in conjunction with Carbonic
Acid.
When the decomposition has been effected the Sodium Carbonates are separated
from the Sulphate of Ammonia and the results of the decomposition may be
employed for useful purposes in the arts.
'

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Eustace Carey and Ferdinand Hurter in the Patent Office on the
11th June 1884.
EUSTACE CAREY and FERDINAND HURTER of Widnes in the County of Lancaster
"IMPROVEMENTS IN THE MANUFACTURE OF SODA AND CHLORINE COMPOUNDS
FROM SODIUM CHLORIDE
"
This Invention relates to the manufacture of soda and chlorine compounds from
sodium chloride and consists in firstly effecting the decomposition of sodium
chloride by means of sulphuric acid and obtaining sodium sulphate and hydro-
chloric acid and then effecting the decomposition of a solution of the sodium
sulphate by the employment of ammonia in conjunction with carbonic acid so as
to obtain sulphate of ammonia and sodium carbonates such decomposition being
capable of being effected in a manner and in apparatus similar to that now
employed or capable of being employed in the production of carbonates of soda
from chloride of sodium by the employment of ammonia in conjunction with
carbonic acid.
When the decomposition has been effected the sodium carbonates are separated
from the sulphate of ammonia and the results of the decomposition may be
employed for useful purposes in the arts.
We
In carrying out our Invention we decompose common salt (sodium chloride) in
ordinary cast iron decomposing pans with sulphuric acid or otherwise and thus
obtain hydrochloric acid gas by the ordinary methods as is well understood
then calcine the acid sodium sulphate in a suitable furnace such for example as that
which is described in Letters Patent granted to Henry Deacon and numbered (176
of 1876) and thus obtain a further quantity of hydrochloric acid The hydrochloric
acid may be utilised in any well known manner as is perfectly well understood.
Or we manufacture sodium sulphate and hydrochloric acid by the method which is
known as Hargreave's method.
Sodium sulphate thus or otherwise obtained we employ for the purpose of
carrying out our invention. We dissolve the sulphate of soda in water or in
residual weak solutions of sulphate of soda obtained in the latter stages of our
process until the solution has a density corresponding from 50° to 60° on Twaddells
hydrometer.
Owing to sulphate of soda when made in the manner above described being
usually contaminated with iron and lime salts and also with free sulphuric acid we
either add (in quantity ascertained by testing) dry carbonate of soda to the dry
sulphate of soda before dissolving it or we add to the solution of sulphate of soda a
solution of carbonate of soda until the mixture reacts slightly alkaline. We thus
neutralize the free acid and precipitate any iron and lime contained in the solution.
Or we add to the solution of sulphate of soda milk of lime which will neutralize the
free acid and precipitate any iron and magnesium contained in the solution but
which will not entirely free the solution from lime.
The solution which holds in suspension carbonate of lime ferrous and ferric
oxides and other insoluble substances is then run into reservoirs where these
insoluble substances are allowed to subside and the solution is allowed to cool to a
temperature of about 100° Fahrenheit.
Or the solution may be passed through a filter press and cooled by artificial
means such as causing cold water to surround or to circulate in a worm placed
within the receptacle for the reception of the solution of sulphate of soda
The sediment which has collected at the bottom of these reservoirs or in the

page_text: The dilute
filter is washed with water to prevent loss of sulphate of soda,
solution obtained by this washing is used instead of water for dissolving further
quantities of sulphate of soda.
"
33
The clear solution of sodium sulphate thus resulting is then charged with
ammonia to such an extent that for every 100 parts of sodium sulphate which
the solution contains there shall be present about 24 or 25 parts of ammonia (NH3)
The ammonia gas for this purpose is evolved in a Coffey or other suitable
still either from the ammoniacal water of gas works in the first instance or from
the decomposition by means of lime of the sulphate of ammonia obtained during
the process.
If the solution of sulphate of soda be allowed to cool below 90° Fahrenheit
after having been charged with ammonia, sulphate of soda will separate out in
crystals, since sulphate of soda is sparingly soluble in solutions of ammonia
It is therefore necessary to maintain the solution at a minimum temperature of
about 90° Fahrenheit. On the other hand it is not advisable to allow the
temperature to rise much beyond 100° Fahrenheit because at higher temperatures
the pressure which it is necessary to employ in the operations hereinafter described
becomes inconveniently great.
It is advisable to introduce carbonic acid gas as soon as the solution has been
rendered sufficiently ammoniacal (which must be ascertained by testing) for the
reason that sulphate of soda is much more soluble in solutions of carbonate of
ammonia than in solutions of caustic ammonia. The carbonic acid gas for this
purpose is obtained partly from some suitable source such as from a lime kiln or
from the combustion of "generator" gas and partly from heating the bicarbonate
of soda obtained during the process as hereinafter described
It is advisable to cool this carbonic acid gas before passing it into the ammonical
solution of sulphate of soda It is also desirable to have this carbonic acid as
pure as possible; it should not contain less than 20 per cent by volume of carbonic
acid. The heat generated by the absorption of the carbonic acid gas assists in
bringing again into solution any portion of the sulphate of soda which may have
crystallized out or may have been precipitated by the ammonia. The operation of
carbonating is greatly hastened by agitation and it will generally be found that
the passage of the gas through the liquid causes sufficient agitation for the purpose
The carbonating must be continued until sufficient carbonic acid has been absorbed
in a quantity which would be sufficient to convert the whole of the ammonia into
bicarbonate of ammonia if the carbonic acid were all combined with ammonia It
is not necessary to apply any great pressure until the whole of the ammonia has
been converted into mono-carbonate but from this point pressure must be applied
which must be the greater the higher the temperature of the solution and the
poorer the quality of the carbonic acid gas This pressure may be obtained by
causing the gas to pass through a sufficient aggregate depth of liquid or to force
itself through a loaded valve We find that if the temperature is kept at 90°
Fahrenheit the pressure which must be applied as a minimum may be calculated by
the following rule. Divide the number 550 by the percentage of the carbonic acid
in the gas. The result indicates the pressure in pounds per square inch,
atmospheric pressure included, so that we have to deduct 15 lbs for the atmospheric
pressure in order to find at how many pounds pressure above the atmospheric
pressure we have to work. If for instance the gas contains 25 per cent of carbonic
acid we divide 550 by 25 which gives 22 lbs atmospheric pressure included, or by
taking off the 15 lbs due to the atmospheric pressure we find that 7 pounds is the
smallest pressure with which we can work at 90° Fahrenheit with a gas containing
25 per cent of carbonic acid We have ascertained by experiment that 550 is the
number to be employed in calculating the necessary pressure corresponding to 90°
Fahrenheit, but for higher temperatures larger numbers must be used We find
that for a temperature of 100° Fahrenheit the number is 950 and the minimum
pressure (atmospheric pressure included) is found by dividing 950 by the
percentage of carbonic acid in the gas, whatever that may be Thus with 25 per

page_text: 950
cent carbonic acid in the gas and 100° Fahrenheit, the minimum pressure at which
we can work becomes =38 lbs per square inch atmospheric pressure included
or 38-15 23 lbs per square inch above the atmospheric pressure.
We prefer
however to work at higher pressures say from 30 to 40 lbs per square inch.
When sufficiently carbonated bicarbonate of soda separates as a fine crystalline
powder; the solution is then allowed to cool so that as little bicarbonate of soda as
possible may remain in solution The bicarbonate of soda is then separated by
filtration from the mother liquor which then contains sulphate of ammonia, sulphate
of soda, and bicarbonate of ammonia.
The bicarbonate of soda is freed as much as possible from the mother liquor by
first filtering in a vacuum filter or in a filter press and afterwards by washing with
water In place of the filter a centrifugal hydro-extractor may be used
$
The bicarbonate of soda is generally even after washing contaminated with
bicarbonate of ammonia which must be recovered For this purpose and also in
order to recover the one half of the carbonic acid contained therein, the bicarbonate
of soda is heated in closed or partially closed vessels and the ammonia carbonic
acid and water which are evolved are drawn away by suitable means as is well
understood and used again for saturating the ammoniacal sulphate of soda solution.
By these means the bicarbonate of soda is transformed into anhydrous mono-
carbonate of soda of great purity which we calcine still further if it is desired to
render it denser-Furnaces such as are used for finishing soda ash by makers of
Leblanc" soda are well adapted for this purpose.
The solution of sulphate of ammonia containing some sulphate of soda and
bicarbonate of ammonia (which we afterwards term the residual solution) may be
first freed from volatile ammonical salts by distillation, the ammonia or carbonate
of ammonia being absorbed or condensed by passing it into water or into a solution
of sulphate of soda If it is desired to recover and use again in the process the
whole of the ammonia, we add to the residual solution thus freed from volatile
ammoniacal salts by distillation, or to the original residual solution, caustic lime or
milk of lime in sufficient quantity to convert the whole of the ammoniacal salts
into caustic ammonia, which is readily performed in the cold. We filter this
solution of caustic ammonia containing the undecomposed sulphate of soda and
some caustic soda from the sulphate of lime and use this solution after saturating
it with fresh sulphate of soda for the production of a further quantity of
bicarbonate of soda by subjecting it again to the action of carbonic acid gas having
previously added if necessary more ammonia
Or we add caustic lime or milk of lime to the residual solution in the still after
having distilled off the ammonia which is volatile at the boiling point and after
adding the lime continue the distillation until all the ammonia has been driven off.
This ammonia gas is then used for saturating solutions of sulphate of soda. The
liquid left in the still contains sulphate of soda and very little sulphate of lime
The lime contained therein is removed by adding a little carbonate of soda and
filtering when the solution may be used for dissolving fresh quantities of sulphate
of soda. Or if we desire to utilize the sulphate of ammonia contained in the
residual solution otherwise than by using it again in the process we free the
residual solution first by distillation from the volatile ammonia and then separate
by evaporation and fishing out the crystals of sulphate of ammonia so long as they
continue to be deposited free or tolerably free from sulphate of soda. When
sulphate of soda begins to deposit with the sulphate of ammonia we cease to
evaporate any further and treat the solution then left with lime in one or other of
the two methods described for the treatment of the original residual solution.
Any apparatus which is now in use for the manufacture of soda from common
salt by the direct ammonia process may be readily adapted to the foregoing
operations by the addition thereto of apparatus for decomposing salt and the
manufacture of hydrochloric acid either by sulphuric acid or by sulphurous acid.
This apparatus for the decomposition of salt by either one or the other method is
well known and we have consequently not given any drawings thereof But in

page_text: order to render clearer the description of our invention we append drawings of an
arrangement of apparatus we may employ to carry our Invention into effect-
We do not however limit ourselves to this arrangement of apparatus, as other
suitable arrangements may be employed; that shewn by our drawings and
hereinafter described we give merely as an example of the best apparatus with
which we are acquainted for carrying our Invention into effect.
Figure 1 of the annexed drawings represents in section the apparatus we
employ for preparing the solution of sulphate of soda--A is a wrought iron vessel
placed at a sufficiently bigh level to allow the solution to flow by gravitation to
any of the other parts of the apparatus in which it may be wanted This vessel
is filled with water or with weak solutions of sulphate of soda. The sulphate of
soda which is to be dissolved is charged in any convenient manner into the iron
basket or cage B. Steam is admitted and the agitator C set in motion by suitable
gearing indicated at D in order to hasten the solution and mix it well with the
carbonate of soda used for neutralising.
When the solution is sufficiently saturated and has a strength of about 50°
to 60° Twaddell at or near the boiling point and has been rendered properly
alkaline it is run off by a valve at E into reservoirs F F where the solution is
allowed to settle and to rest until it is sufficiently cool, say about 100° Fahrenheit
The solution is then withdrawn which may be conveniently effected by means
of the swivel syphons indicated at G and conveyed to the saturators by means of a
pipe H.
The sediment which deposits at the bottom of the reservoirs F can be
withdrawn by valves at I and is washed in a filter press or any other suitable
apparatus or it may be washed in the reservoirs F but it is preferable to wash it
elsewhere. The dilute solution obtained by washing this sediment is again used
for dissolving sulphate of soda in the dissolving apparatus A.
Figures 2 and 3 represent an apparatus for treating the sulphate of soda solution
with ammonia and carbonic acid-Figure 2 is a sectional elevation and Figure 3
is a plan. The apparatus consists of a series of wrought iron vessels capable of
withstanding a working pressure of at least 30 to 40 lbs per square inch Each
of these vessels is provided with a man-hole for cleaning and small taps to permit
samples of the contents to be withdrawn. The said vessels are supported at
different levels on suitable frame-work so that the solution may flow from one
vessel to the next below it by gravitation and the difference of level between any
two of these vessels must be equal at least to the depth of the liquid within the
vessel. At the lowest level there are two vessels marked V¹ which work alternately
while the higher vessels V2 V3 and V work continuously. All of these vessels V₁
to V contain ammoniacal solution of sulphate of soda which gradually descends
from the highest vessel V₁ to the lowest V₁ and in descending meets a current of
carbonic acid Gas (preferably cooled) which is propelled by a pump and enters the
system of vessels, through the pipe L. At there are two valves which permit
the gas to pass into either or both of the two vessels V as required. The Gas
then passes down to the bottom of either or both of the vessels V¹ where it is
distributed by perforated pipes or by a rose. It ascends through the solution and
leaves the vessel by the pipe L' passing through the valves or one of them and
enters the vessel V2. At the bottom of this vessel the gas is again distributed by
a perforated pipe or rose and in a similar manner passes by the pipe L to the
vessel V³ and by the pipe L³ to the vessel V which it leaves by the pipe L*.
Most of the carbonic acid is now absorbed but the gas carries with it a certain
amount of ammonia. In order to absorb this ammonia the Gas is next passed
through the vessels V5 and V which are in every respect similar to the other
vessels but which contain a solution of sulphate of soda obtained from the
reservoirs F (Figure 1) The gas washed by passing twice through this solution,
videlicet once through the vessel Vs and thence by the pipe L' through the
vessel V leaves the vessel V6 by the pipe L' and is deprived of the last traces of
ammonia by passing the said gas through a coke scrubber or other suitable

page_text: apparatus, such as is used in gas works in which apparatus the ammonia is
absorbed either by water or by sulphuric acid.
The sulphate of soda solution which serves to wash the gas flows from the
reservoirs F (Figure 1) into the vessel V8 by the pipe H From the vessel VⓇ it
flows into the vessel V By passing through these two vessels the solution is
partially charged with ammonia or carbonate of ammonia, but the quantity of
ammonia thus brought into solution is not sufficient and more must be added. For
this purpose vessels in sufficient number are provided; there are two shewn
at M M in the Drawing. These are wrought iron vessels provided with a jacket
and agitators The jacket serves to prevent the contents from overheating by
allowing cold water to circulate between the jacket and the vessel. These vessels
are connected with the vessel V' by pipes and stopcocks m in such manner that the
said vessels may be filled by opening the said stopcocks m and the air escape
valves q.
When one of the said vessels is filled the corresponding cocks are shut
and ammonia gas is admitted which is evolved in a Coffey" still and brought to
the vessel by a pipe K provided with stop cocks ¹³ one for each vessel.
"
When the solution is rendered sufficiently ammoniacal (which must be ascertained
by withdrawing a sample and testing it, a sampling tap being provided for the
purpose) it is pumped through the pipe N into the vessel V wherein the carbonating
begins. The liquid then gradually descends from vessel to vessel until it arrives at
one or other or both of the vessels V₁ where the carbonating is completed. The
absorption of the carbonic acid causes the solution to become warm. This is but
of little consequence in the vessels V₁ and V³, but in the lower vessels V2 and V¹
the temperature ought not to rise much above 100° Fahrenheit.
In order to be able to regulate the temperature we place between every two of
the cylinders a trough P containing cold water into which trough we place a coil
of pipes as shewn Through these coils of pipes the solution passes as it flows from
one cylinder to the next one and is thus cooled to the requisite temperature. In
practical working when the solution arrives at the lowest level it is caused to flow
into the one vessel of the pair marked V₁ which has just been emptied whilst the
gas is made to pass through the one which happens to be full. When the latter
one is completely carbonated and the other one filled the gas is caused to pass
through the one just filled by operating the valves. The contents of the other
Vessel V¹ are then emptied by a cock The two valves are always both of them
open except when it is desired to clean out one of the vessels V¹.
The contents of this vessel when completely carbonated consist of a solution of
sulphate of ammonia, a little sulphate of soda, and bicarbonate of ammonia, which
solution holds in suspension bicarbonate of soda as a fine crystalline precipitate.
This liquid is allowed to cool and is then filtered through a suitable filter This
may be of the ordinary kind, the construction of which being well understood we
do not consider it necessary to further describe The bicarbonate of soda collected
on the filters is washed with water to free it from mother liquor. The bicarbonate
of soda is then heated to drive out the ammonia and the one half of the carbonic
acid which it contains, the ammonia is absorbed in water and the carbonic acid
passed again into the system by means of a pump.
The solution which remains after filtering out the bicarbonate of soda and which
we term the residual solution, contains the sulphate of ammonia some sulphate of
soda and bicarbonate of ammonia The solution is distilled with lime in a "Coffey"
still and yields ammonia gas necessary for charging the sulphate of soda solutions.
Losses of ammonia during the process must of course be made good from time to
time. The liquors remaining in the still, contain the sulphate of soda in solution
and sulphate of lime in suspension The said liquors are filtered or allowed to
settle and the clear liquid is again used for dissolving fresh sulphate of soda in the
vessel A whilst the sulphate of lime is utilised either as manure or otherwise
disposed of
If however we simply causticise these residual solutions by lime in the cold
without distillation the annaratus must be worked slightly differently. The

page_text: operations in the vessels V¹ to V will remain exactly the same but instead of
charging the vessels V³ and V* with a solution of sulphate of soda derived from
reservoirs F we now fill and supply them with the residual solutions coming from
the filters Having passed through the vessels Vs and Vo, these residual solutions are
then treated and agitated in a closed vessel with caustic lime which readily converts
in the cold all the ammonia salts the solution contains into caustic ammonia. The
solution is then filtered from the sulphate of lime and is passed into & vessel similar
in every respect to the vessel A, Figure 1, with the exception that it is closed and
that the solution is only heated to 100° Fahrenheit and saturated with sulphate of
soda at that temperature. When so saturated the solution flows into reservoirs
similar to those shewn at F but also closed to prevent loss of ammonia as it is
filtered, and if necessary supplied with more ammonia in the cylinders M¹ M². It
is then pumped into the vessel V*.
We have given the apparatus herein described and illustrated in the accompanying
drawings as being that most suitable for carrying the Invention into effect, but
we do not claim this apparatus in itself alone under this present patent, as it forms
the subject matter of an application for Letters Patent to Holbrook Gaskell and
Ferdinand Hurter made on the Tenth June One thousand eight hundred and
eighty four
Having now described and particularly ascertained the nature of our said
Invention and the manner in which the same is or may be used or carried into
effect we would observe in conclusion that what we consider to be novel and original
and therefore claim as the Invention secured to us by the hereinbefore in part
recited Letters Patent is.
The manufacture of soda (meaning thereby bicarbonate and carbonate of soda)
from sodium chlorine by converting it into sodium sulphate and treating the
sulphate when in solution with ammonia and carbonic acid at about the temperatures
and under the pressures substantially as herein before described.
In witness whereof I Ferdinand Hurter on behalf of Eustace Carey and
myself have to this our Specification set my hand and seal this eleventh day of
June One thousand eight hundred and eighty four
FERDINAND HURTEK.
(L.S.)