Improvements in Extracting Sugar from its Solutions.
Year: 1895

page_text: Improvements in Extracting Sugar from its Solutions.
I, ALFRED WOHL, of 5 Joachimsthalerstrasse Charlottenburg, near Berlin in
the Kingdom of Prussia, German Empire, Chemist, do hereby declare the nature
of this invention to be as follows:-
It is a well known fact that sugar and oxide of lead (PbO) will combine to
form a compound, practically insoluble provided the lead oxide (PbO) be employed
in a finely divided state, and be maintained in intimate contact with the solution.
This course has indeed been suggested before now by Dubrunfaut for the extraction
of sugar from molasses. But neither Dubrunfaut nor any of the subsequent
chemists have succeeded hitherto in obtaining by the aid of lead-oxide (PbO) a
sufficiently complete separation of sugar in the form of lead, saccharate, nor in
effecting this object in such a manner that the same lead oxide (PbO) may be used
for the purpose over and over again. By the experiments and investigations I have
made I have ascertained that there are special conditions upon the fulfilment of
which depends a uniformly satisfactory formation of lead-saccharate and enabling
Dubrunfaut's suggestion to be carried out as a practically or commercially
workable process, and I have rendered the process so simple, economical and
convenient, that it now constitutes the most advantageous method hitherto devised
for extracting sugar from solutions.
As to
It is a well known scientific fact that pure plumbic oxide (PbO) is obtainable
in two modifications or forms viz.: as red oxide and as yellow oxide.
amorphous lead-oxide (PbO) which is obtained by the oxidation of metallic lead,
or by heating white lead or nitrate of lead, it constitutes a mixture of these red
and yellow lead-oxides in varying proportions.
I have found that the behaviour of these two modifications of lead-oxide (PbO)
in relation to sugar solution is different.
Approximately pure red oxide (PbO), for example, red flake-litharge, when
finely ground and sifted, will act upon sugar solutions in an almost imperceptible
way, if unassisted by heat, its action being slow even in the case of 50 per cent.
solutions, and so at the temperature considered as most favorable to such action
i.e. 80 to 90° Centigrade. It is only by the use of an excess of sugar aided by a
long digestion that pure red lead-oxide (PbO) is completely converted into lead-
saccharate. Yellow oxide (PbO) however (obtained for example, by heating the
same ground flake-litharge, for a short time at a temperature of 600° Centigrade)
will "bind " sugar almost instantaneously, and at an ordinary temperature,
provided other conditious be satisfactory. For this reason the said yellow modifi-
cation may be distinguished by the term "active" oxide. The inequality of the
action on saccharine solutions of amorphous lead-oxide (PbO)-which is obtained
by burning basic carbonate of lead-therefore results from the varying proportion
in which the yellow and red modifications are present in a given case, according as
the burning of the basic lead carbonate has been effected at a higher or lower
temperature. Thus where the burning temperature does not exceed that which is
required for eliminating the carbonic acid from the basic lead carbonate, say from
200 to 300° Centigrade scarcely anything but red oxide (PbO) is obtained. Where
a dark red heat is employed (about 600° Centigrade) all the basic lead carbonate
becomes converted into soft porous oxide (PbO) which is as yellow as sulphur ;
and this oxide is obtained in a perfectly pure condition by being rapidly cooled.

page_text: In this form lead-oxide (PbO) is most active as a sugar extracting medium. By
still further raising the temperature, the yellow oxide (PbO) becomes harder and
harder until at cherry red heat, it will fuse.
When subjected to compression by grinding or triturating for example, the
yellow lead-oxide (PbO) will change to the red modification. This change may
be met, however by grinding the yellow oxide (PbO) in the wet, it being
immaterial whether the oxide be ground separately while being moistened with
water, and then mixed with the sacchariferous liquor in a pulpy, or semi-liquid
condition, or whether the grinding operation be performed in the liquor itself, from
which it is desired to extract the sugar, and at the same time with the formation
of the saccharate. Considering that the yellow plumbic oxide (PbO) acts at an
ordinary temperature, no appreciable advantage is derivable from applying heat
during the formation of the lead saccharate, where pure yellow oxide (PbO) is
used. But where the lead oxide (PbO) available consists in a mixture of the
yellow and red modifications part of the red modification will also be caused to
combine with sugar by employing a higher temperature. On the other hand the
time occupied by the reaction depends upon the more or less extensive area of the
"active surface" that is to say upon the greater or less excess of lead oxide (PbO)
employed and the fineness of its division.
In the case of impure sacchariferous solutions, besides sugar, also the non-
saccharine bodies present, enter into reaction with the lead-oxide (PbO). This
reaction mainly results in forming basic salts of lead, whereby alkali is liberated.
Ordinary beet-root sugar molasses for example, will thus consume or absorb at
least 20 per cent of the yellow or "active" lead-oxide (PbO) for every 100 parts
of molasses.
Now I have ascertained that a reaction between oxide of lead (PbO) and the
salt like non-saccharine bodies present may be almost wholly avoided by adding such
an amount of alkali, as is required for raising the alkalinity of the liquor to the
same, or a higher degree, as that to which it would rise in consequence of the
reaction with the lead-oxide (PbO). Such a displacing effect may be brought
about by any alkaline agent, such as hydrated alkali, ammonia, alkaline earths, or
alkaline carbonates.
The most effective of these agents will prove to be hydrated sodium and
potassium on account of their high coefficient of basicity. But potassium hydrate
will be the more serviceable as it does not interfere with the employment of the
residuary lye for the extraction of potash, and it is recuperated from the
"schlempekohle" together with that originally contained in the liquor without
occasioning any extra expense.
As the basic nature of hydrated potash is very strong in comparison with that of
lead-oxide (PbO) comparatively small quantities of hydrated potash will suffice
for preventing secondary reactions, so that the lead oxide (PbO) employed is
utilised for the formation of lead-saccharate in a very thorough and complete
manner so as to render unnecessary any considerable excess of that agent.
The increased purity of the lead-saccharate thus obtained, affords the additional
advantage of facilitating regeneration of the lead-oxide (PbO) which is recuperated
in a purer state, while on the other hand, the increased alkalinity of the
sugar solution becomes in itself, a means of accelerating the formation of lead
saccharate.
But
Experiments made with pure sugar, solutions have shewn that, where small
quantities of alkali (say from 5 to 20 cubic centimetres of normal potash or soda
lye for every 100 grammes of sugar) are added-the temperature not being unduly
raised the sugar would be bound and separated out of its diluted solutions more
rapidly and completely than it would without any such addition of alkali.
whereas pure lead-saccharate in consequence of such added alkali, is separated in a
state of such fine division that the sliny precipitate is scarcely capable of being
filtered, this somewhat serious drawback does not make itself felt where the
saccharine liquor (molasses etc.) is less pure.

page_text: The results of experiment as above summarised shew that what is essential
above all, to a satisfactory yield of lead-saccharate from sacchariferous solutions
treated with oxide of lead (PbO) is that a lead oxide (PbO) should be employed
which contains as large a proportion of the yellow or "active" modification as
possible.
Concentrated solutions, both at ordinary and comparatively high temperatures,
either with or without alkaline additions, may by such means in a very short time,
be completely freed from the sugar, they contain, provided that the surplus
quantity of oxide of lead (PbO) employed is sufficiently large. More diluted
solutions will give equally satisfactory results if the re-action he allowed to take
place at normal, or but a slightly raised temperature, which in no case should
exceed 70 or 80° Centigrade and where, moreover, alkali is added. Under these
circumstances, the "binding" effect will not be delayed to any appreciable extent,
even though 5 or more parts of water be added for every one part of molasses.
In the case of ordinary beetroot sugar molasses, I employ from one to two per
cent, of potassium hydrate (KOH) and also 75 parts of properly burnt yellow lead-
oxide (PbO) for every 100 parts of molasses; and this, without any heating,
sufficient to cause the whole of the sugar to be so completely converted into lead
saccharate in a space of two hours, that a laevorotary liquor results. Where 80 per
cent. of "active lead oxide (PbO) is used, this effect is obtained in about one
hour. Where the proportion is increased to 90 per cent., it will be obtained in less
than half an hour, and at 100 per cent., within five minutes, or rather under. This
result may be obtained, too, with 70 per cent. of "active" lead-oxide (PbO), if the
mixture, after being well stirred, be allowed to stand at rest for from ten to fifteen
hours at the ordinary temperature. Theoretically, the quantity of active lead-
oxide (PbO) requisite for the formation of bi-saccharate of lead is rds of the
quantity of sugar to be transformed; for instance if the molasses contain 50 per
cent. of sugar, the percentage of active lead-oxide (PbO) would have to be
66 per cent.
Where the lead-oxide (PbO) has not been properly burnt, being, for example,
too hard, or baving still retained a deep yellow colour, there will be a reduction
of the effect amounting to 20 per cent. or more, according as more, or less, red
oxide (PbO) is present.
The dilution of the saccharate, for the purpose of accelerating filtration, is
preferably effected with a quantity of warm water sufficient to produce a pulp like
mass capable of running at a temperature of from 40° to 50° Centigrade. For
washing water at from 40° to 50° should preferably first be used and then the
temperature be raised by slow degrees so that the filtered liquor is finally collected
at from 70 to 75° Centigrade. By these means the lixiviation is very considerably
accelerated without any loss or waste the fact being that lead saccharate will
scarcely dissolve in water even with the assistance of heat. In alkaline lyes,
however, such as are obtained by additions of alkali or simply by the action of
oxide of lead (PbO) upon impure solutions of sugar such as molasses etc. experi-
ment has shewn that the solubility of saccharate of lead is small at temperatures
under 60° Centigrade only, a quantity of lead saccharate corresponding to about
01 to 0.15 per cent. of sugar being dissolved. When the temperature exceeds
60° Centigrade the quantity of lead saccharate that is dissolved rapidly increases
keeping pace with the rise of the temperature so that in such an emergency
considerable losses of sugar might take place. It is obvious that these losses can
be avoided by removing the greater part of the alkali by washing.
For the purpose of extracting the sugar from the lead saccharate the latter is
treated with carbonic acid or subjected to carbonation care being taken to cause
intimate contact between the gaseous acid and the saccharate by providing suitable
mechanical devices such for instance as metallic strainers inserted into the
saturating pans means for stirring up the precipitate from the bottom and
the like.
If the precipitate obtained in the carbonating stage after being freed from the

page_text: sugar by washing and subsequently dried be heated to calcining temperature a
portion of the lead present in the form of basic carbonate will separate out in the
metallic state forming minute globules which under the continued action of heat,
will unite, but which will oxidise but slowly and incompletely even if air be
admitted. The proportion of metallic lead thus separating out will be more or less
considerable according to the greater or less percentage of organic matter present.
An imperative condition of the satisfactory performance of the process of sugar
extracting by means of the production of saccharate of lead is that the lead oxide
(PbO) should be recoverable over and over again in the form of the yellow
modification without any appreciable expense or waste. This condition may be
successfully realised by conducting the burning of the precipitate obtained in the
carbonating stage according to the following method.
The separation of metallic lead will be prevented by heating the said precipitate
whilst admitting air-for a somewhat lengthy period the temperature being
slowly and gently raised however so as to be maintained below the melting point of
lead. The mass will first assume a black colour owing to the formation of
sub-oxide and of metal in a finely divided state both of which being then gradually
converted into yellow oxide of lead (PbO). The precipitate may in this process
be compressed in partly dried state into solid blocks bricks cylinders or the like
before burning. In consequence of the expulsion of water and carbonic acid these
blocks and the like will become sufficiently porous to be capable of being burnt
throughout in the presence of air without falling to pieces. When the black
colour has disappeared but not before the temperature may be further raised in
order to dispel the remainder of carbonic acid and to change the dark yellow or
brownish oxide (PbO) obtained in the first place from the basic carbonate of lead
to the sulphur yellow modification. During this latter operation the supply of air
should be as completely as possible cut off because failing this the brownish yellow
oxide (PbO) would become converted into minium at the parts of the furnace that
are insufficiently hot. Minium will, upon being further heated yield up again the
oxygen by the absorption of which it has been produced and thus be reduced to
yellow oxide (PbO) but in order to do this it requires a higher temperature applied
for a larger period than is necessary for the conversion of the red lead oxide (PbO)
into the yellow lead oxide (PbO).
Where the burning operation has not been properly conducted and where greater
or less quantities of brownish yellow oxide of lead (PbO) or of minium have in
consequence formed these are unavailable in the following stage of saccharate
formation. They need not on this account however be separated from the pure
yellow oxide (PbO) present but may be allowed to pass through all the subsequent
stages of operation; and when the next burning stage is conducted in the proper
manner they will be converted in the active yellow modification. Then the red
lead oxide (PbO) at a suitable temperature will become converted into yellow
oxide (PbO) while the minium will give up oxygen even at a moderate temperature
to the organic substances present so that in this case proportionately less air or no
air at all need be admitted.
Where in the production of lead saccharate sufficient quantities of alkali are
added the proportion of salt like non-saccharine bodies present in the precipitate
resulting from the carbonating stage is greatly reduced as has already been
stated; so that in this case a purification of the said precipitate is not in every
case necessary.
The alumina the silicic acid and the oxide (sesqui-oxide) of iron present in the
said precipitate may be rendered inocuous by the following means.
By mixing together the washed precipitate with finely divided magnesia or
carbonate of magnesia (say about 2 or 3 per cent. of MgO of the quantity of
oxide of lead (PbO) and then drying the mixture and calcining it the said
impurities become wholly converted into harmless magnesium combinations and
a perfectly pure lead cxide (PLO) of a clear sulphur yellow colour will be
obtained. An action similar to that of magnesia is exercised by baryta, strontia

page_text: and lime and the carbonates of these in the proportion in which when subjected
to calcination they give off carbonic acid (CO,) and become converted into
oxide.
I have also found that when prior to calcination the precipitate is mixed with
a dilute solution of soda potash or ammonia and the mixture is heated to a high
temperature a black tinged lye is obtained which contains in the form of alkali
salts nearly all the organic and inorganic impurities of the precipitate that are
capable of combining with alkali. Where the above mixture is heated in open
vessels a violent foaming takes place. Moreover it has been ascertained that the
decomposition is the more complete and requires the less alkali in excess the
higher the temperature at which the mixture is digested. It is therefore
advisable to mix the precipitate to which is added the requisite proportion of
potash with water into a thick pulp and to heat the same in a closed boiler or pan
by the direct action of steam at an additional pressure of from 4 to 5 atmospheres.
Under these conditions the reaction will be completed in less than half an hour
and a proportion of potash corresponding to two or three times the equivalent of
the inorganic acids fixed by lead oxide will suffice to convert both the inorganic
and organic acids into potassium salts. The use of potash for thus purifying the
precipitate has proved to be most serviceable since any quantity of it, in excess
of what is required may be readily and completely washed out with hot water.
The lye thus obtained is added to the liquid resulting from the washing of the
saccharate and utilised in the production of "schlempekoble" as described.
Carbonate of sodium however is very tenaciously retained in the condition of a
double lead salt and can scarcely be fully removed from the precipitate even with
the employment of large amounts of water.
The sugar solutions obtained by the carbonation of the lead saccharate until
the whole of the sugar has been separated are perceptibly coloured a brown hue by
the addition of sulphuretted hydrogen after the separation of the precipitate or
in other terms the solubility of the carbonate of lead in a sugar solution (which
may be represented by the proportion of 1 to 50,000 for a 20 per cent. solution) is
too great for the present purpose. But under certain suitable conditions that
solubility may be reduced to zero by the presence of dissolved carbonate of lime.
Pfeiffer" and "Langen" have shewn that by repeatedly treating diluted sugar
solutions containing lead with lime and carbonic acid, the proportion of lead
contained in such solutions is greatly reduced so that in the sugar separated from
the solution in the condition of saccharate of lime mere traces of lead can be
detected. bave since found that the solubility of carbonate of lead in sugar
solutions in the presence of carbonate of lime will be the more reduced the higher
the temperature and the higher also the degree of concentration of the sugar
solution but invariably to a very great extent. Sacchariferous solutions no matter
of what degree of concentration (say 20° 33° or 50° Brix) from which the main
portion of the lead has been separated by means of carbonic acid by being treated
once with about to of a part of lime to 100 parts of sugar and with carbonic
acid at from 80° to 95° Centigrade and then filtered at this temperature will be
freed from lead to such an extent that no further reaction can be observed when
the solution is first mixed with acetic acid and then with sulphuretted hydrogen
though in a 50 per cent. sugar solution that has not been treated as stated
sulphuretted hydrogen will enable 1 part of lead to 20,000,000 parts of solution
or to 10,000,000 parts of sugar to be detected. Under such conditions (viz. the
employment of concentrated solutions and comparatively high temperatures) the
solubility of the carbonate of lead in sacchariferous solutions in the presence of
carbonate of lime is therefore many times less than the solubility of any one of the
least soluble compounds in water (BaSO, 1 : 430,000 etc. up to AgBr 1: 2,000,000).
Accordingly with the view to the total elimination of all traces of lead the liquor
separated by filtration from the lead precipitate is subjected after concentration
to from 40° to 50° Brix to a defecating process in the presence of to part of
calciumhydrate (CaO) for every 100 parts of sugar present and at a temperature

page_text: at from 80 to 90° Centigrade after which by filtration at a high temperature the
liquor is separated from the small quantity of precipitated matter.
I have also ascertained that a further method for the reliable elimination of
the least traces of lead that may be left consists in heating the concentrated
solutions with animal charcoal used in the proportion of from 1 to 2 parts for
every 100 parts of sugar or with very small quantities of magnesium powder (say
from 1 to 2 grammes of sugar). The subsequent use of either of these two media
suffices to obviate even the remotest possibility of any traces of lead remaining in
suspension in the fluid in consequence of any leakage in the filtering press or of
their finding their way into the solution accidentally at any subsequent period.
Especially where charcoaling is used not only every trace of any lead salt that
may by any chance have been dissolved, greedily absorbed ; but in addition to this,
a perfect mechanical clarification is obtained with certainty.
EXAMPLE:
600 kilogrammes of soft sulphur yellow lead oxide (PbO) is uniformly ground
in a mill preferably a vertical mill together with 400 litres of water for from
10 to 15 minutes. Then 800 kilogrammes of molasses 400 litres of water and
25 litres of "technical" 50 per cent. potash lye are added and thoroughly stirred
and mixed for another 10 cr 15 minutes until the mass begins to thicken. The
mass is drawn off into reservoirs so long as it is capable of running and is here
left for from an hour and a half to two hours. Within this time the lead saccharate
will have congealed into a viscid mass, and any reaction will have ceased.
The saccharate is then removed from the reservoirs and mixed with a small
quantity of hot water (say from to 1 part of water to 100 parts of molasses)
and the thick semi-liquid mass thus obtained the temperature of which should
preferably not exceed from 40° to 50° Centigrade is filtered by means of a filtering
press and then washed with water which at first should be not hotter than from
40° to 50° but afterwards should be higher.
The mill may be charged with a fresh supply of material directly the preceding
charge has been removed.
Dated this 29th day of November 1895.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.
COMPLETE SPECIFICATION.
Improvements in Extracting Sugar from its Solutions.
I, ALFRED WOHL, of 5 Joachimsthalerstrasse, Charlottenburg near Berlin in
the Kingdom of Prussia, German Empire, Chemist, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :—
This invention relates to the extraction of sugar from sacchariferous liquors
containing salts, such as molasses and other salty after-products obtained in the
manufacture of sugar, and it has for its object to operate this extraction in a
simpler and more economical manner than heretofore. To this end the invention
is based on the saccharate-forming properties of lead oxide, that is to say protoxide
of lead (PbO), and it consists in an improved process comprising the production
and decomposition of the lead-saccharate, as also the regeneration of the lead
protoxide from the waste for use in a new cycle of operations, and the elimination
of the last traces of lead from the solution obtained by the decomposition of the
lead-saccharate.
It is a well-known fact that sugar and oxide of lead (PbO) will combine into a

page_text: saccharate practically insoluble, provided the lead oxide (PhO) be employed in a
finely divided state and be maintained in intimate contact with the solution of sugar..
This course has, indeed, been suggested before now by Dubrunfaut for the extraction
of sugar from its solutions. But neither Dubrunfaut nor any of the subsequent.
chemists have succeeded hitherto in obtaining by the aid of lead oxide (PbO) a
sufficiently complete separation of sugar in the form of lead-saccharate, from
saccharine solutions containing salts, such as molasses and other after-products.
obtained in the manufacture of sugar, nor in effecting this object with such
recuperation of the lead oxide employed that the same may be used for the purpose
over and over again without appreciable losses. It is by applicant's experiments.
and investigations that the special conditions have been detected upon which
depends a uniformly satisfactory formation of lead-saccharate, and which therefore
enable him to carry out Dubrunfaut's suggestion as a practically or commercially
workable process.
It is a well-known scientific fact that pure plumbic oxide (PbO) is obtainable
in two modifications viz.: as red oxide and as yellow oxide. As to amorphous
lead-oxide (PbO), which is obtained by the oxidation of metallic lead, or by
heating white lead or nitrate of lead, it constitutes a mixture of those two
modifications in varying proportions.
Now I have found that the behaviour of these two modifications of lead-oxide.
(PbO) in relation to sugar solutions is by no means the same.
Approximately pure red oxide (PbO), for example red flake-litharge, when
finely ground and sifted, will act upon sugar solutions in an almost imperceptible.
way if unassisted by heat, its action being slow even in the case of 50 per cent.
solutions and so at the temperature considered as most favorable to such action, i.e.
80 to 90° Centigrade. It is only by the use of an excess of sugar aided
by a long digestion that pure red lead-oxide (PbO) is completely converted
into lead-saccharate. Yellow oxide (PbO), however, (obtained, for example, by
heating the same ground flake-litharge, for a short time at a temperature of
600° Centigrade) will bind sugar almost instantaneously, and at an ordinary
temperature, provided other conditions be satisfactory. For this reason, the said
"yellow" modification may be distinguished by the term "active" oxide. The
inequality of the action on saccharine solutions of amorphous lead-oxide (PbO)-
which is obtained by burning basic carbonate of lead-therefore results from the
varying proportion in which the yellow and red modifications are present in a given
case, according as the burning of the basic lead carbonate has been effected at a
higher or lower temperature. Thus, where the burning temperature does not
exceed that which is required for eliminating the carbonic acid from the basic lead
carbonate, say from 200 to 300° Centigrade, scarcely anything but red oxide (PbO).
is obtained. Where a dark red heat is employed (about 600° Centigrade) all the
basic lead carbonate becomes converted into soft, porous oxide (PbO) which is as
yellow as sulphur; and this oxide is obtained in a perfectly pure condition by being
rapidly cooled. In this form lead-oxide (PbO) is most active as a sugar extracting
medium. By still further raising the temperature, the yellow oxide (Pb).
becomes harder and harder, until, at cherry red heat, it will fuse.
When subjected to compression (i.e. when ground or triturated)-as has already
been previously observed the yellow lead-oxide (PbO) will change to the red
modification. This change may be met, however, by grinding the yellow oxide
(PbO) in the wet state ("wet grinding"), it being immaterial whether the oxide
be ground separately while being moistened with water, and then mixed in the state
of a thin pulp with the sacchariferous liquor, or whether the grinding operation be
performed in the liquor itself from which it is desired to extract the sugar, and at
the same time with the formation of the saccharate. Considering that the yellow
plumbic cxide (PbO) acts well at an ordinary temperature, no appreciable
advantage is derivable from applying heat during the formation of the lead-
saccharate, where pure yellow oxide (PbO) is used. But where the lead-oxide
(PbO) available consists in a mixture of the yellow and red modifications, part of

page_text: the red modification will also be caused to combine with sugar by employing a
higher temperature. On the other hand the time taken up by the reaction depends
upon the more or less extensive area of the "active surface," that is to say, upon
the greater or less excess of lead-oxide (PbO) employed, and the fineness of its
division.
In the case of impure sacchariferous solutions, such as molasses and other salty
after-products obtained in the manufacture of sugar, besides sugar, also the non-
saccharine bodies present, that is to say the salts contained in the molasses etc.,
enter into reaction with the lead-oxide (PbO). This reaction mainly results in
forming basic salts of lead whereby alkali is liberated from said nou-saccharine
bodies. For instance, taking the potassium chloride present in the molasses, a
reaction will take place according to the following equation: 6 PbO + 2 KCI
+ H2O = 2 KOH + Pb,O,Cl₂. Ördinary beet-root sugar molasses, for example.
will thus consume or absorb at least 20 per cent. of the yellow or "active" lead
oxide (PbO) for every 100 parts of molasses.
Now I have ascertained that this useless consumption of lead oxide (PbO) may
be almost wholly avoided by adding such an amount of free alkali to the solution
as is required for raising the alkalinity of the liquor to the same, or a higher
degree as that to which it would rise in consequence of the reaction between the
lead oxide (PbO) and the said non-saccharine bodies. The preventive effect of
the said addition of alkali is based upon the fact that basic lead salts are readily
decomposed by a strong alkaline solution, so that, if there is sufficiently free alkali
added to the molasses &c, any basic lead salt present will at once be re-decomposed ;
from this it results that the presence of a quantity of free alkali in the molasses etc.
as stated, will not allow basic lead salts to be formed or to subsist. This effect will
be obtained by any alkaline agent, whether hydrated alkali, ammonia, alkaline
earths, or alkaline carbonates. The most effective of these agents, will prove to
be hydrated sodium and potassium on account of their high coefficient of basicity.
But potassium hydrate will be the more serviceable as it does not prejudice the
employment of the residuary lye for the extraction of potash, and it is recuperated
from the salin together with that originally contained in the liquor without
occasioning any extra expense.
As the basic nature of hydrated potash is very strong in comparison with that
of lead-oxide (PbO), comparatively small quantities of hydrated potash will suffice
for excluding secondary reactions, so that the lead-oxide (PbO) employed is utilised
for the formation of lead saccharate in a very thorough and complete manner so as
to render unnecessary any considerable excess of that agent.
The increased purity of the lead-saccharate thus obtained affords the additional
advantage of facilitating regeneration of the lead-oxide (PbO) which is recuperated
in a purer state, while, on the other hand, the increased alkalinity of the sugar
solution becomes, in itself, a means of accelerating the formation of lead
saccharate.
But
Experiments made with pure sugar solutions have shown that, where small
quantities of alkali (say from 5 to 20 cubic centimetres of normal potash or soda
lye for every 100 grammes of sugar) are added, the temperature not being unduly
raised the sugar would be bound and separated out of its diluted solutions more
rapidly and completely than it would without any such addition of alkali.
whereas in this case pure lead-saccharate, in consequence of such additional alkali,
is separated in a state of such fine division that the slimy precipitate is scarcely
capable of being filtered, this somewhat serious drawback does not make itself felt
where the saccharine liquor is less pure, consisting in molasses or other salty after-
products of the manufacture of sugar.
The results of experiment, as above summarised, show that what is essential,
above all, to a satisfactory yield of lead saccharate from sacchariferous solutions
treated with oxide of lead (PbO), is, that a lead-oxide (PbO) should be employed
which contains as large a proportion of the yellow or "active" modification as
possible.

page_text: Concentrated solutions, both at ordinary and comparatively high temperatures,
either with, or without, alkaline additions, may, by such means, be completely freed
from the sugar they contain, in a very short time, provided that the surplus
quantity of oxide of lead (PbO) employed is sufficiently large. More diluted
solutions will give equally satisfactory results, if the reaction be allowed to take
place at normal or but a slightly raised temperature which in no case should
exceed 70 or 80° Centigrade, and where, moreover, alkali is added. Under these
conditions the "binding" effect will not be delayed to any appreciable extent, even
though 5 or more parts of water be added for every one part of molasses. The
reason for restricting the temperature to the limit stated is dictated by the
experience that the formation of lead saccharate is the more retarded by
the presence of water the higher the temperature of the mixture.
In the case of ordinary beetroot sugar molasses, I employ from one to two per cent.
of potassium hydrate (KOH), and 75 per cent. of "active" lead-oxide (PbO) for
every 100 per cent. of molasses; and this, without any heating, is sufficient to cause
the whole of the sugar to be so completely converted into lead saccharate in a
space of two hours, that a lavorotary liquor results. Where 80 per cent. of "active"
lead exide (PbO) is used, this effect is obtained in about one hour's time.
Where
the proportion is increased to 90 per cent., it will be obtained in less than half an
hour, and at 100 per cent. within five minutes or rather under. This result may be
obtained, too, with 70 per cent. of "active" lead-oxide (PbO), if the mixture, after
being well stirred, is allowed to stand at rest for from ten to fifteen hours at the
ordinary temperature. Theoretically, the quantity of "active" lead oxide (PbO)
requisite for the formation of bi-saccharate of lead is 3rds of the quantity of sugar
to be transformed; for instance, if the molasses contain 50 per cent. of sugar, the
percentage of active lead-oxide (PbO) would have to be 66 per cent.
Where the lead-oxide (PbO) has not been properly burnt, being, for example,
too hard to having still retained a deep yellow colour, there will be a reduction of
the effect amounting to 20 per cent. or more, according as more, or less, red
oxide (Pb) is present.
The dilution of the saccharate, for the purpose of accelerating filtration, is
preferably effected with a quantity of warm water sufficient to produce a pulp like
mass capable of running at a temperature of from 40° to 50° Centigrade. For
washing first water at from 40 to 50° should preferably be used, and then the
temperature be raised by slow degrees so that the filtered liquor is finally collected
at from 70 to 75° Centigrade. By these means the lixiviation is very considerably
accelerated without any loss or waste, the fact being that lead saccharate will
scarcely dissolve in water even with the assistance of heat. In alkaline lyes,
however, such as are obtained by additions of alkali or simply by the action of
oxide of lead (PbO) upon impure solutions of sugar such as molasses and other
salty after products obtained in the manufacture of sugar, experiment has shewn
that the solubility of saccharate of lead is small at temperatures under 60° Centigrade
only, a quantity of lead saccharate corresponding to about 01 to 0.15 per cent. of
sugar being dissolved. When the temperature exceeds 60° Centigrade, the quantity
of lead saccharate that is dissolved rapidly increases, keeping pace with the rise of
the temperature so that in such an emergency considerable losses of sugar inight
take place. It is obvious that these losses can be avoided by removing the greater
part of the alkali by washing.
For the purpose of extracting the sugar from the lead saccharate the latter is
preferably diluted with water or a sugar solution and then treated with carbonic
acid, or subjected to carbonation, at ordinary temperature or a temperature not
higher than 70-80° Centigrade, care being taken to cause intimate contact between
the gaseous carbonic acid and the saccharate by providing suitable mechanical
devices such for instance as metallic strainers inserted into the saturating pans,
means for stirring up the precipitate from the bottom, and the like. The sugar
solution employed for diluting may consist in the filtered liquor resulting from a
previous carbonation, or even in molasses etc., provided the proportion of same be
13

page_text: such as to leave the lead oxide in excess, as required. The carbonation is
complete as soon as the polarising power of the liquor ceases to be increased.
If the precipitate obtained in the carbonating stage, after being freed from the
sugar by washing and subsequently dried, be heated to calcining temperature, a
portion of the lead present in the form of basic carbonate will separate out in the
metallic state, forming minute globules which, under the continued action of heat,
will unite, but which will oxidise but slowly and incompletely even if air be
admitted. The proportion of metallic lead thus separating out will be more or
less considerable according to the greater or less percentage of organic matter
present.
An imperative condition of the satisfactory performance of the process of sugar
extracting by means of the production of saccharate of lead is that the lead
oxide (PbO) should be recoverable over and over again in the form of the yellow
modification without any appreciable expense or waste. This condition may be
successfully realised by conducting the burning of the precipitate obtained in the
carbonating stage according to the following method.
The separation of metallic lead will be prevented by beating the said precipitate
whilst admitting air-for a somewhat lengthy period, the temperature being
slowly and gently raised, however, so as to be inaintained below the melting point
of lead. The mass will first assume a black colour owing to the formation of sub-
oxide of lead (Pb,O) and of metallic lead in a finely divided state, both of which
being then gradually converted into yellow oxide of lead (PbO). When the
black colour has disappeared, but not before, the temperature is further raised up
to 600° Centigrade in order to dispel the remainder of carbonic acid and to change
the dark yellow or brownish oxide (PbO) obtained in the first place from the basic
carbonate of lead, to the sulphur yellow modification. During this latter operation
the supply of air should be as completely as possible cut off because failing this,
the brownish yellow oxide (PbO) would become converted into minium at the parts
of the furnace that are insufficiently hot. Minium will, upon being further heated,
yield up again the oxygen by the absorption of which it has been produced and
thus be reduced to yellow oxide (PbO), but in order to do this, it requires a higher
temperature applied for a larger period than is necessary for the conversion of the
red lead oxide (PbO) into the yellow lead oxide (PbO). The precipitate may in
this process be compressed in partly dried state into solid blocks, bricks, cylinders
or the like, before burning. In consequence of the expulsion of water and carbonic
acid these blocks and the like will become sufficiently porous to be capable of being
burnt throughout in the presence of air without falling to pieces.
Where the burning operation has not been properly conducted, and where greater
or less quantities of brownish-yellow oxide of lead (PbO) or of minium have in
consequence formed, these are unavailable in the following stage of saccharate
formation. They need not on this account, however, be separated from the pure
yellow oxide (PbO) present, but may be allowed to pass through all the subsequent
stages of operation and when the next burning stage is conducted in the proper
manner, they will be converted in the active yellow modification. Then the red
lead oxide (PbO) at a suitable temperature will become converted into yellow
oxide (PbO), while the minium will give up oxygen even at a moderate temperature
to the organic substances present so that in this case proportionately less air or no
air at all need be admitted.
Where in the production of lead saccharate sufficient quantities of alkali are
added, the proportion of salt like non-saccharine bodies present in the precipitate
resulting from the carbonating stage is greatly reduced, so that in this case a
purification of the said precipitate is not in every case necessary.
The alumina the silicic acid and the oxide (sesqui-oxide) of in present in the
said precipitate may be rendered innocuous by the following means. By mixing
together the washed precipitate with finely divided magnesia or carbonate of
magnesia (say about 2 or 3 per cent. of MgO of the quantity of oxide of lead (PbO)),
and then drying the mixture, and calcining it, the said impurities become wholly

page_text: converted into harmless magnesium combinations, and a perfectly pure lead
oxide (PbO) of a clear sulphur yellow colour will be obtained. An action similar
to that of magnesia is exercised by baryta, strontia and lime, and the carbonate
of these.
I have also found that when prior to calcination the precipitate is mixed with a
dilute solution of soda, potash or ammonia, and the mixture is heated to a high
temperature, a black tinged lye is obtained which contains in the form of alkali
salts nearly all the organic and inorganic impurities of the precipitate that are
capable of combining with alkali. Where the above mixture is heated in open
vessels a violent foaming takes place. Moreover, it has been ascertained that the
decomposition is the more complete and requires the less alkali in excess the higher
the temperature at which the mixture is digested. It is therefore advisable to
mix the precipitate, to which is added the requisite proportion of potash, with
water into a thick pulp aud to heat the same in a closed boiler or pan by the direct
action of steam at an additional pressure of from 4 to 5 atmospheres. Under these
conditions the reaction will be completed in less than half an hour, and a proportion
of potash corresponding to two or three times the equivalent of the inorganic acids
present in the form of lead salts will suffice to convert both the inorganic and
organic acids into potassium salts. The use of potash for thus purifying the
precipitate has proved to be most serviceable since any quantity of it in excess of
what is required, may be readily and completely washed out with hot water.
lye thus obtained is added to the liquid resulting from the washing of the saccharate
and thus utilised in the production of salin as described.
The
Carbonate of sodium, however, is very tenaciously retained in the condition of a
double lead salt and can scarcely be fully removed from the precipitate even with
the employment of large amounts of water.
The sugar solutions obtained by the carbonation of the lead saccharate, until
the whole of the sugar has been separated, are perceptibly coloured a brown hue
by the addition of sulphuretted hydrogen after the separation of the precipitate, or
in other terms, the solubility of the carbonate of lead in a sugar solution (which
may be represented by the proportion of 1 to 50,000 for a 20 per cent. solution) is
too great for the present purpose. But under certain suitable conditions that
solubility may be reduced to zero by the presence of dissolved carbonate of lime.
"Pfeiffer" and "Langen" have shewn that by repeatedly treating diluted sugar
solutions containing lead, with lime and carbonic acid, the proportion of lead
contained in such solutions is greatly reduced, so that in the sugar separated from
the solution in the condition of saccharate of lime mere traces of lead can be
detected. I have since found that the solubility of carbonate of lead in sugar
solutions in the presence of carbonate of lime will be the more reduced, the higher
the temperature and the higher also the degree of concentration of the sugar
solution, but invariably to a very great extent. Sacchariferous solutions no
matter of what degree of concentration (say 20°, 33° or 50° Brix) from which the
main portion of the lead has been separated by means of carbonic acid, by being
treated once with about to of a part of lime to 100 parts of sugar and with
carbonic acid at from 80° to 95° Centigrade, and then filtered at this temperature,
will be freed from lead to such an extent that no further reaction can be observed
when the solution is first mixed with acetic acid and then with sulphuretted
hydrogen, though in a 50 per cent. sugar solution that has not been treated as stated,
sulphuretted hydrogen will enable lead to be detected when present in the
proportion of 1 part of lead to 20,000,000 parts of solution or to 10,000,000 parts
of sugar. Under such conditions (viz. the employment of concentrated solutions
and comparatively high temperatures) the solubility of the carbonate of lead in
sacchariferous solutions in the presence of carbonate of lime is therefore many
times less than the solubility of any one of the least soluble compounds in water
(BaSO, 1: 430,000 etc. up to AgBr 1: 2,000,000). Accordingly with the view to
the total elimination of all traces of lead, the liquor separated by filtration from
the lead precipitate, is subjected, after concentration to from 40° to 50° Brix, to a

page_text: defecating process in the presence of to ½ part of calcium hydrate Ca(OH), for
every 100 parts of sugar present and at a temperature at from 80 to 90° Centigrade
after which, by filtration at a high temperature, the liquor is separated from the
small quantity of precipitated matter.
I have also ascertained that a further method for the reliable elimination of the
least traces of lead that may be left, consists in heating the concentrated solutions
with animal charcoal used in the proportion of from 1 to 2 parts for every 100 parts
of sugar, or with very small quantities of powdered magnesium (say from 1 to
2 grammes for every 100 kilogrammes of sugar). The subsequent use of either of
these two media suffices to obviate even the remotest possibility of any traces of
lead remaining in suspension in the fluid in consequence of any leakage in the
filtering press or of their finding their way into the solution accidentally at any
subsequent period. Especially where charcoaling is used, not only is every
trace of any lead salt that may by any chance have been dissolved, greedily
absorbed, but in addition to this, a perfect mechanical clarification is obtained
with certainty.
EXAMPLE:
600 kilogrammes of soft sulphur yellow lead oxide (PbO) are uniformly ground
in a mill, preferably a vertical mill, together with 400 litres of water for from
10 to 15 minutes. Then 800 kilogrammes of molasses, 400 litres of water, and
25 litres of "technical" potash lye having 50 per cent., are added and thoroughly
stirred and mixed for another 10 or 15 minutes until the mass begins to thicken.
The mass is drawn off into reservoirs so long as it is capable of running, and is
here left for from an hour and a half to 2 hours. Within this time the lead
saccharate will have congealed into a viscid mass, and the reaction will be
complete.
The saccharate is then removed from the reservoirs and mixed with a small quantity
of hot water (say from to one part of water to 100 parts of molasses) and the
thick semi-liquid mass thus obtained, the temperature of which should preferably
not exceed from 40° to 50° Centigrade, is filtered by means of a filtering press and
then washed with water which at first should be not hotter than from 40° to
50° Centigrade, but afterwards should be applied with a higher temperature as
described.
The mill may be charged with a fresh supply of material directly the preceding
charge has been removed.
The washed saccharate is first diluted by stirring it with water or with a
saccharine solution, and then treated with carbonic acid until the polarising power
of the liquor ceases to be increased, when the latter is separated from the pre-
cipitate by filtration. The precipitate which mainly consists of basic carbonate of
lead, is transformed into yellow lead-oxide (PbO) in any convenient manner to
re-use the latter in a following operation. The saccharine solution is purified
from the last traces of lead as described or in any other known manner, and finally
worked as usual.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The improved process of extracting sugar from molasses and other salty after-
products obtained in the manufacture of sugar by means of lead oxide (PbO) which
essentially consists in the yellow modification of lead oxide and is applied under
conditions as stated.
2. In carrying out the improved process referred to in the first claim, the
addition, as described, of alkaline hydrates or carbonates for the purpose of
decreasing the reaction between the yellow lead oxide and the salt like non
saccharine bodies present.
3. In carrying out the improved process referred to in the first claim, washing

page_text: the filtered lead-saccharate first with water at a moderate temperature, and then
with water of gradually raising temperature, as and for the purpose stated.
4. In carrying out the improved process referred to in the first claim, depriving.
the sugar solution obtained by the carbonating stage, from the last traces of lead
by treating the concentrated solution with calcium hydroxide and carbonic acid
under conditions as stated, and separating the liquor from the precipitate while
hot, with or without subsequently heating the filtered liquor with charcoal or
magnesium powder, substantially as described.
5. In carrying out the improved process referred to in the first claim, regenerating
yellow lead oxide from the precipitate obtained in the saturating stage, by heating
the said precipitate first at a low temperature with access of air and subsequently
up to about 600° Centigrade with the exclusion of air, substantially as described.
6. In carrying out the improved process referred to in the first claim, adding an
alkaline earth in the form of hydrate or carbonate to the precipitate obtained
in the saturating stage, before treating said residue as stated in the 5th claim,
substantially as and for the purpose stated.
7. In carrying out the improved process referred to in the first claim, regenerating
yellow lead oxide from the precipitate obtained in the saturating stage, by boiling
said precipitate with a dilute alkaline solution, separating the liquor from the-
residue, and burning the latter, substantially as described.
Dated the 22nd August 1896.
JOHNSONS & WILLCOX,
Agents.