SULPHITATION
IN
WHITE SUGAR
MANUFACTURE
SULPHITATION
IN
WHITE SUGAR
MANUFACTURE
BY
FRANCIS MAXWELL,
Ph.D., A.M.I.Mech.E., F.C.S.
Graduate of the Swiss Federal Polytechnicum (Zurich).
Late Technical Adviser to The Credit Foncier of Mauritius, Ltd,
Consulting Sugar Engineer and Chemist.
LONDON :
NORMAN RODGER,
ST. DUNSTAN'S HILL, E.C.
1916.
TO
MY RESPECTED FATHER
THIS WORK
IS GRATEFULLY DEDICATED.
PREFACE.
The Sulphitation Process, as applied in the manufacture of
Plantation White Sugar, in cane sugar producing countries, is a
subject of such wide-spread interest, and the developments in its
application so remarkable, that the author trusts a book on this
all-important subject may be found both timely and useful.
Although the greater part of the data presented in this book
is the result of investigations by the author, made whilst acting in
responsible positions in the different leading Plantation White Sugar
producing countries, he has also gratefully referred to results
obtained by his colleagues in various parts of the world, chiefly
Harloff& Schmidt, Pellet, Horsin-Deon, Dr. Zerban, and others.
He also desires to acknowledge his indebtedness to The Sugar
Machinery Manufacturing Co., Ltd., London, for photographs and
descriptions of apparatus willingly given.
F. MAXWELL.
SYDENHAM, LONDON,
May, 1914.
EDITOR'S NOTE.
Dr. Maxwell's manuscript was completed early in 1914, and was under
revision with a view to publication in September, 1914, when war broke out.
Being in Germany at the time, he was, unfortunately, interned as a civilian
prisoner of war ; and as his release at this date still seems remote, it has been
decided not to delay publication further.
August, 1916.
CONTENTS.
INTRODUCTION.
PAGE
Sulphur and its Compounds in the Manufacture of
Sugar. i
CHAPTER I.
SULPHUR, ITS ORIGIN, PREPARATION AND PROPERTIES
Origin of Sulphur - ... 3
Refining .... 3
Nature and Properties - ... 4
CHAPTER II.
SULPHUROUS ACID, ITS PREPARATION, CHEMICAL
PROPERTIES AND ACTION
Liquid Sulphurous Acid - ... 5
Sulphurous Acid Gas - - 5
Properties . . 5
Bleaching Action - 7
Action on Iodine - 7
Generation - - - 8
Combustion Temperature - g
Sublimators . g
Drying the Air . . g
Vlll.
CHAPTER III.
GENERATING PLANTS FOR SULPHUROUS ACID GAS, AND
SULPHITATION VESSELS FOR JUICE AND
SYRUP
PAGE
Description of Apparatus used in Mauritius 10
Quarez Sulphitation Installation 12
Apparatus as used in Java 15
Sulphitation Vessels 17
Sulphitation Tanks 19
CHAPTER IV.
THE CONTROL OF THE SULPHUROUS ACID GAS
GENERATING STATION
Quantity of Lime for Air Drying 20
Manipulation of the Sulphur Furnace 20
Regulation of the Air Supply - 20
Consumption of Sulphur 21
CHAPTER V.
ANALYSIS OF THE SULPHUROUS ACID GAS
Theoretical Purity - 23
Methods of Analysis 23
CHAPTER VI.
ACTION OF SULPHUROUS ACID ON JUICES
Purifying Action 26
Bleaching Action
Neutralizing Action
Reducing Viscosity
Preservative Action - 28
IX.
CHAPTER VII.
PRINCIPLES OF THE APPLICATION OF SULPHITATION
TO JUICE
PAGE
Sulphitation after Tempering the Juice - 29
Tempering 29
Sulphitation 31
Sulphitation before Tempering the Juice - 31
High Glucose Proportion 34
Dextran Fermentation 34
Viscous Juices 35
Control of the Sulphitation of the Juice 36
Testing for Neutrality 37
CHAPTER VIII.
SULPHITATION OF THE SYRUP, AND OF MOLASSES
Decolorizing Agents 38
Sulphitation Operation 38
Apparatus for Intermittent Sulphuring - 39
Continuous Sulphitation Apparatus - 39
Control of the Sulphitation of Syrup- 39
Determination of Extent of Sulphitation - 40
Iodine Titration Apparatus - 41
Methods of Titration 42
Sulphitation of Molasses - 44
Inversion in Syrup 44
Corrosion in Syrup Apparatus 45
Sodium Hydrosulphite, or " Blankit " 46
Syrup or Molasses — Order of Application of different
Agents 47
X.
CHAPTER IX.
THE SULPHITATION PROCESS IN PRACTICE
PAGE
General Scheme of Operation 49
Purification of the Mill Juice 49
Tempering - 49
Sulphitation 49
Heating 50
Cleaning 50
Evaporation - 5 1
Treatment of the Syrup - 51
Treatment of the First Molasses - 51
Clarifying the Molasses - - - 52
Treatment of the Second Molasses - - 52
Boiling . 52
The Two-Sugar Method - - - 53
Single Sugar Process - - - 53
Blueing the Sugars 54
CHAPTER X.
PROCESSES ADOPTED BY THE LEADING WHITE SUGAR
COUNTRIES
1. JAVA.
The " Bach " Treatment of Syrup 55
2. MAURITIUS.
Sulphitation - - - - 56
Liming and Measuring - - - 56
Heating the Juice - ... 55
Defecation --.... - 56
XI.
PAGE
Filtering 55
Evaporating and Treatment with Phosphate - - 57
Subsiding . 57
Boiling - - - 57
Molasses 5g
3. NATAL.
Wax Separation - - - - - 58
SUMMARY.
Tempering - ...... 59
Preparation of Lime-Milk - - - 61
Sulphitation of the Juice - - - - 62
Generation of Sulphurous Acid ... 54
Treatment of the Syrup and Molasses - - - 66
LIST OF ILLUSTRATIONS.
FIGURES IN TEXT.
Fig. PAGE
1 A FORM OF SULPHITATION APPARATUS USED IN
MAURITIUS 11
2 QUAREZ SULPHITATION INSTALLATION - 13
3 APPARATUS FOR SULPHITATION AS USED IN JAVA, &c. 16
4 THE " SULPHUR Box " - 18
5 APPARATUS FOR ANALYSING SULPHUROUS ACID GAS 24
6 IODINE TITRATION APPARATUS - 41
7 SIMPLE TITRATION APPARATUS 43
8 VIVIEN TUBE 43
PLATES.
FACING PAGE
1 MODERN SULPHUR FURNACES 18
I SULPHITATION VESSELS WITH STIRRING GEAR 19
3 BATTERY OF SULPHITATION TANKS - - . 30
SULPHITATION
IN
WHITE SUGAR MANUFACTURE,
INTRODUCTION.
SULPHUR AND ITS COMPOUNDS IN THE MANUFACTURE
OF SUGAR.
HISTORY OF THE APPLICATION.
The use of the compounds of sulphur as purifying agents in the
manufacture of sugar may be considered to date as far back as
1792, when Achard, the founder of the beet sugar industry, first
applied a diluted solution of sulphuric acid to beet juice with a view
to precipitating organic constituents, especially albuminoids, the
free acid being subsequently neutralized by means of an addition of
chalk before the juice was heated.
This process appeared to work satisfactorily, but its application
did not gain ground, the simple method of defecation being generally
preferred.
It was, however, the French chemist Proust, in 1810, who was
the first to propose the application of sulphurous acid to the process
of juice clarification. In the following year Dapriez took out the
first patent for its practical application as a substitute for the
sulphuric acid of Achard's process.
In 1825 a modification was introduced by Dombasle, and per-
fected by Dubrunfaut, to whom a patent was granted in 1829 for a
process of sulphitation, in which sulphurous acid was brought into
contact with beet pulps, and the juice submitted to the action of a
larger and more constant proportion of lime, to be subsequently
neutralized, either by sulphuric or sulphurous acid. In practice,
however, the process did not prove to be a success.
2 : Introduction.
Subsequently, Stolle (1838) obtained a patent upon the ground
that sulphurous acid would act as a decolorizing substitute for bone
black. Other investigators, including Merge, Boulon (1846) and
Melsen (1849), carried out extensive experiments on the application
of different sulphites, such as sulphite of lime, sulphite of alumina,
etc., to this problem. The results, however, were unsatisfactory
and impracticable, and consequently the idea of their application
was abandoned.
The keen researches along the above lines did not remain con-
fined to beet sugar fabrication, but soon spread to the sugar cane
countries, for in the colony of Mauritius in 1865, Dr. leery conducted
successful experiments, which have been of appreciable benefit to
the industry in that island. His method was shortly afterwards
introduced into Java.
Opinions as to the value of sulphurous acid as a purifying
agent, and the most effective method of its application, were for a
long time by no means concordant. The next patent, granted to
Seyferth (1869) was issued upon the basis of introducing the acid
directly into the vacuum pans during the boiling of syrup. This
process came into vogue in Germany and France, but certain
technical difficulties caused it to be gradually abandoned.
Numerous subsequent experiments, extending over a number of
years, have elucidated to a great extent the problem encountered in
applying sulphitation processes. Prominent among the numerous
investigators who have been engaged in this field of research are
Basset, Fradiss and Schulze. It was not till 1884, however, that
the sulphitation process in sugar fabrication was finally established.
This was chiefly due to the exhaustive researches of Battut.
In the sugar cane countries, where this process has made rapid
strides, and is at the present day playing the most important part
in the manufacture of superior white plantation sugar, it is evident
that it has been, ever since its establishment, the subject of exten-
sive experiments and considerable improvements. During recent
years the knowledge of this process in cane sugar fabrication has
been greatly extended, notably as the result of valuable researches
by Dr. Zerban, Harloff, Hazewinkel, and others.
CHAPTER I.
SULPHUR.
Its Origin, Preparation and Properties.
Origin. — Sulphur, the material used for the generation of sul-
phurous acid gas in the sulphitation process, is obtained by refining
the crude element occurring widely and abundantly in nature,
especially in connection with volcanoes.
Some of the most important deposits of sulphur in the world are
met with in Sicily, chiefly in the sulphur-bearing zones of Girgenti.
The quarried or mined free sulphur derived from these sources is
always contaminated with impurities, such as limestone, gypsum,
clay, etc., which necessitates a preliminary refining before use.
This process consists briefly in melting the element, either by the
heat of its own combustion, or by other means, and running it off
from the earthy residue.
In Java, the progressive cane sugar producing island, various
attempts have been made to use local sulphur which occurs abundantly
on the numerous volcanoes, with however little success, owing to
the presence of volcanic impurities. It was only quite recently that
a source of very pure sulphur was discovered on a volcano in one
of the Moluccan islands, since when a sulphur refinery has been
built, and is supplying a number of factories in Java.
The sulphur produced appears to be of very good quality, con-
taining some 99'8 per cent, of pure sulphur. It may be interesting
to give here Leon's description1 of the refining process as applied
in Java : —
Refining. — "' The crude sulphur is charged into a cast iron tank.
" This is heated by means of coal, by which process the raw material
" is melted. Organic substances, such as pieces of wood, etc., will
" rise and float on the surface of the molten mass. They are
" removed by means of perforated iron skimmers. Sand and clay
" will obviously be precipitated and deposited at the bottom of the
1 Java Archief, No. 8, 1913.
A2
Chapter I.
4
tank. This heating process is kept up for some five hours, during
"which time volatile impurities of low boiling point will have
" escaped."
" Subsequently the fluid mass is discharged into a closed furnace,
"or so-called 'cornue,' in which its temperature is further raised
" to 400° C by means of coal. The distillation of the sulphur is
" conducted by leading the sulphur vapours into a cooling chamber.
" The temperature prevailing in the interior of this chamber is
"gradually brought to about 130° C, so that the distillate accumu-
" lates at the bottom as a liquid, which is tapped off from time to
" time to be cast into the customary form of rods."
Nature and Properties. — Sulphur exists in several allotropic
modifications, but the most important one in our case is the ordinary
or rhombic sulphur, the properties of which are therefore dealt with.
Commercial roll sulphur has an average specific weight of T92 to
2*0. Its composition is naturally subject to considerable variations.
Italian and French sulphurs usually contain 96'3 to 99' 1 per cent.
of sulphur, 2*4 per cent, to O2 per cent, of ash and O'l percent.
of arsenic. An official analysis of the Javanese sulphur gives the
following figures : — Sulphur 99'8 per cent., moisture O04 per cent.,
ash 0'02 per cent., arsenic absent. Obviously this kind of sulphur
is exceptionally pure.
Commercial sulphur forms yellow crystals which melt at 113° C,
ignite in air at 250° C, and boil at 445° C under ordinary pressure.
On ignition the sulphur burns with a characteristic blue rlame ;
just above the boiling point the vapour is orange yellow in colour
but on continued heating it darkens, becoming deep red at 500° C,
while at higher temperatures it again lightens, becoming straw-
yellow at 650° C.
Other interesting phenomena are witnessed when sulphur is
heated above its melting point. The solid melts to a pale yellow
liquid, which on continued heating gradually darkens and becomes
more viscous, the maximum viscosity occurring at 180° C, the
product being then dark red in colour. On further heating the
viscosity diminishes, while the colour remains the same.
CHAPTER II.
SULPHUROUS ACID.
Its Preparation, Chemical Properties, and Action.
For the sulphitation process in the manufacture of sugar, the
dioxide of sulphur (802) commonly known as sulphurous acid is
used. It may be applied in either of two forms, as a liquid or as a
gas, the gaseous form being more generally adopted.
Liquid Sulphurous Acid. — In European beet sugar factories the
use of liquid sulphurous acid is frequently met with, owing to the
convenience of its manipulation and transport, in addition to the
saving in generating apparatus.
The sulphurous acid gas is liquefied under pressure in suitable
steel receptacles, in which it comes into the factory. The principal
advantages of fluid sulphurous acid are that it produces an exceed-
ingly pure saturation gas of a constant SC>2 content, avoiding the
obnoxious occurrence of sublimation in pipes, etc., and that it is
readily manipulated.
The fact that up to the present this form of sulphurous acid is more
expensive than that which is obtained by the simple combustion of
sulphur locally, constitutes the main reason why it has not made
its way into the tropical sugar countries, where the cost of transport
of heavy receptacles is a prime factor. In Europe the cost in
connection with the application of liquid sulphurous acid during the
past few years has been reduced to almost equal that of sulphur
furnaces, as the liquid acid can be transported in bulk in specially
constructed tanks, from which it can be transferred by means of
compressed air.
The Sulphurous Acid Gas, which is almost exclusively used in
cane sugar factories, is generated by the simple process of combus-
tion of commercial roll sulphur in suitable furnaces.
When sulphur burns in air or oxygen, sulphur dioxide (sulphurous
anhydride) is formed according to the equation : —
S + O2 = SO2
6 Chapter II.
At the same time, small quantities of sulphur trioxide (SO;*) are
formed, which render the gas obtained by this combustion" more or
less foggy.
Properties of Sulphurous Acid. — Before proceeding further, it
may be well to consider those properties of sulphurous acid which
may play an important part in the process of its generation and
practical application.
Sulphur dioxide is a colourless gas, possessing a characteristic
suffocating odour. It is more than twice as heavy as air, its specific
gravity being 2'26. It is readily soluble in water, its solubility at
various temperatures being as follows : —
1 volume of water at 0° C dissolves 79'79 vols. SO<>
1 „ „ 20" „ 39-37 „ „
1 „ „ 40* „ 18-77 „ „
The solution is strongly acid, and is regarded as sulphurous
acid, the gas having entered into chemical union with the water : —
SO, + H20 == H2SOS
When sulphurous acid gas is heated to 1200° C it entirely
decomposes into oxygen and sulphur, thus : —
SO, = S + 0-.
In contact with an excess of oxygen, the sulphurous anhydride
will be transformed into sulphuric anhydride : —
SO, + O - SO.
These two latter actions are of considerable importance, being
detrimental to the successful employment of SO2 as a purifying
agent in sugar manufacture.
According to experiments conducted by Horsin-Deon, the dis-
sociation takes place even below 1200° C, namely, at 800°-900° C.
When this temperature is reached, a series of dissociation processes
occur, viz., first of all, SO2 into S and O2, and this excess of oxygen
enters into combination with SO2 to form SOs ; and again SOs into
SO2 and O.
When dealing with humid gas, the unavoidable formation of
Sulphurous Acid. 7
sulphuric acid is evident. From the above facts, therefore, we
deduce the following conclusions applicable in practice : —
1. High combustion temperatures in sulphur furnaces
are to be carefully avoided.
2. As a precautionary measure, sublimators must be
connected with the sulphur furnaces, to condense the distilled
sulphur.
3. To remove all traces of sulphuric acid from the gas,
an additional gas washer is necessary.
Bleaching Action. — Sulphur dioxide possesses powerfu4 bleach-
ing properties in the presence of water. This bleaching action is
considered to be due to the liberation of hydrogen consequent upon
the formation of sulphuric acid, thus : —
SO- + 2 H2O == H2SO4 + H2
•
The hydrogen thus set free reduces the colouring matter, with the
formation of colourless compounds. In some instances the bleaching
is due to the formation of a colourless compound by the direct
combination of sulphur dioxide with the colouring matter, as it is
found possible to restore the original colour by treatment with
dilute sulphuric acid, or weak alkaline solutions.
Action on Iodine. — In the presence of water, sulphur dioxide
converts iodine into hydriodic acid, giving a colourless solution,
according to the equation : —
SO2 + 2 H->O + l> ^~^ 2 HI + H,SO4
This reaction, however, only takes place when a certain degree
of dilution is maintained, for in a more concentrated solution sul-
phuric acid is reduced by hydriodic acid to sulphur dioxide, according
to the reverse equation given above.
Bunsen has shown that aqueous sulphurous acid can only be
completely oxidized by iodine, as indicated in the foregoing equation,,
when the proportion of sulphur dioxide does not exceed O05 per cent.
When this is exceeded, the second reaction comes into operation.
8 Chapter II.
Generation of Sulphurous Acid.
Precautionary Measures to be observed. — The essential points
to be borne in mind in connection with the generation of sulphurous
acid gas, and the construction and arrangement of sulphurous acid
producing plants, are comprised in the following.
The sulphur is almost exclusively burnt in a cast-iron combustion
chamber, into which the air necessary for the combustion may be
introduced either by compression or suction.
Air Regulation.— The regulation of the quantity of air is of
great importance, for we have seen that lack of air involves an
incomplete combustion of the sulphur, which in its turn promotes
the occurrence of sublimated sulphur in the pipings, and on the
other hand, an excess of air renders the saturation gas generated
too dilute, which affects the sulphitation process.
Taking the latter point into consideration, therefore, it is im-
portant that the sulphur furnaces should always be kept within
reasonable dimensions, otherwise an excessive volume of air would
be necessary for keeping the sulphur burning ; at the same time it
is desirable to establish a correct relationship between the size of
furnace and the air compressor.
Combustion Temperature.— Excessive combustion temperatures
should be avoided ; otherwise, as previously stated, dissociation of
the sulphurous anhydride is apt to occur, in which case a certain
.amount of sulphur in the form of vapour is entrained in the pipings,
.and on cooling becomes re-crystallized, ultimately causing the
pipings to become choked.
Sublimators. In spite of all care and supervision, this pheno-
menon, called sublimation, is bound to occur to a more or less extent,
hence it is imperative to provide such installations with a sublimator,
fitted with an effective water-cooling device.
Drying the Air.— Further, it is essential that the air should be
dried prior to entering the combustion chamber.
Although it has been repeatedly proved that humid air incontro-
vertibly promotes the formation of sulphuric acid, and in spite of
Sulphurous Acid. 9
the destructive consequences of this acid being so well-known, yet
many factories in tropical cane countries still ignore this important
point.
The formation of sulphuric anhydride in the sulphur furnace
may occur, for example, when dissociation takes place, or in the
presence of an excess of air.
In the presence of humidity, the sulphuric anhydride combines
Avith the water, forming sulphuric acid, according to the equation :—
SO, + H2O == H2SO4
Priestley and Berthollet have given us another equation, accord-
ing to which HsSCh may be formed at high temperatures, viz. : —
3 SO-> + 2 H,0 - 2 H2S04 + S
Apart from the notorious inverting properties of sulphuric acid
in sugar solutions, we have the destruction of piping, boilers, etc.,
due to corrosion, which goes hand in hand with the formation of
this acid.
In order to reduce the formation of sulphuric acid to a minimum,
the air for combustion should pass through several layers of quick-
lime prior to entering the sulphur furnace, by which process the
moisture is absorbed. Even then, as explained above, the occurrence
of traces of sulphuric anhydride due to dissociation cannot be
entirely avoided.
Its presence may be obviated by passing the fumes produced in
the sulphur furnace through a washer, where the sulphuric anhydride
readily enters into combination with the water to form sulphuric acid
solution which will remain in the washer.
The final process to wrhich the gas is to be subjected before coming
into contact with the juice to be treated consists in purifying it, by
allowing it to pass through layers of coke or other kindred material,
with subsequent cooling through an efficient water-cooling device.
CHAPTER III.
GENERATING PLANTS
FOR SULPHUROUS ACID GAS.
Sulphitation Vessels for Juice and Syrup.
There are a great number of types of installations for the genera-
tion of sulphurous acid gas. The simplest, but at the same time
most primitive installation imaginable, is such as is still to be met
with in a number of factories in Mauritius.
The plant usually consists of a couple of miniature chimney-like
iron furnaces, the top-ends of which are connected with the sulphita-
tion vessels by means of piping. The air required for the combustion
of the sulphur is drawn into the combustion chamber by means of
an injecting arrangement (Giffard), which carries the sulphur fumes
forward directly into the sulphitation vessels by means of steam.
Owing to the absence of gas purifying and cooling devices, it is
evident that this manner of operation involves a generation of impure
saturation gas, in addition to the occurrence of sulphuric acid and
sublimation products. In a few cases gas washers and sublimators
are employed.
Another apparatus met with in a few factories on that island,
which appears to be appreciated owing to its simplicity, cheapness,
and alleged efficiency, is shown in Fig. 1, a description1 of which is
as follows : —
The installation is composed of—
A sulphitation tank A.
A cast iron furnace B, provided with a slide arranged in such a
manner as to reduce the amount of air entering the chamber to a
minimum.
A refrigerating sublimator C.
A washer D, which consists of a rectangular vessel of solid
antimonized lead, divided vertically into two compartments by means
1Baissac, Soci^te des Chimistes de Maurice, August, 1912.
11
12 Chapter III.
of a leaden partition, leaving a communicating space between the
compartments of one inch from the bottom. This arrangement
enables the washing of the sulphurous gas to be carried out. The
gas is drawn by an injector E through the water, thus ridding it of its
impurities. Juice inlet is 1, juice outlet 2, the washed gas enters
injector chamber by 3, and steam by 4.
The gas washer contains about 20 litres of water, which is
changed at intervals of eight hours. The quantity of sulphuric acid
contained in the water, according to analyses taken on different
occasions, varied from 16 to 28'6 grms. per litre, giving an average of
20'3 grms. of SOa, or 400 grms. per washer during eight hours' work.
At the end of the milling season, a greyish powder is found to
adhere to the partition, principally composed of sulphates and
sulphites of lead, silicon, traces of iron, etc.
The main advantages attributed to the gas washer are that it
retains the SOs formed during the combustion process, and also the
impurities of the sulphur which have not been deposited in the
sublimator.
Quarez Sulphitation Installation.
We now come to an installation which enjoys a wider range of
application, and may be met with in beet sugar as well as in cane
sugar factories, namely the Quarez Sulphitation Plant. It belongs
to the class of continuous Sulphitation apparatus, and owing to its
simplicity as well as efficiency, it is much appreciated.
The installation consists of an ingenious combination of an air
dryer, sulphur furnace, sublimator, juice pump and Sulphitation tank,
which entire arrangement takes up but a small space.
The sulphur is burnt in a rectangular combustion chamber L.
The tray on which the sulphur is charged is moveable for the purpose
of introducing the latter, and also for cleaning ; the door may be
opened without the sulphur fumes escaping into the atmosphere.
The air is drawn from underneath through an air drying device S,
composed of a chamber containing several layers of quicklime, and
thence into the combustion chamber.
Generating Plants.
13
The sulphur fumes pass through a cooling device M, situated on
the top of the furnace, and thence through the sublimator N, con-
sisting of a long vertical pipe, provided with a water-cooling jacket.
FIG. 2.
QUAREZ SULPHITATION INSTALLATION.
The sulphitation tank A is divided into two compartments, the
juice to be sulphitated being introduced into the smaller division C, to
which also the suction of a pump D is attached. The pump draws
14 Chapter III.
the non- or slightly sulphitated juice up and forces it into the injector
F, whence it circulates downwards through the column Q, drawing
the sulphurous acid gas with it into the larger division of the tank.
The juice is thus continuously kept in circulation, until the required
degree of acidity is obtained. The actual sulphitation process there-
fore occurs in the vertical column, where the gas and juice are
intimately mixed.
The gas which has not been absorbed will bubble through the
juice in the tank. The sulphitation tank is provided with a test box
P, and a run-off pipe R.
The sulphitation process is controlled by regulating the quantity
of juice to be treated and the speed of the pump.
The points in connection with the Quarez installation put forward
by its advocates are : —
1. The sulphurous acid gas is introduced into the juice
by means of suction and not forced through by compression.
2. The quantity of juice in contact with the acid is
small, namely, three to four hectolitres.
3. The entrance and discharge of the juice being con-
tinuous, the sulphitation process may be interrupted and
recommenced instantaneously without any inconvenient
consequences.
4. The Quarez apparatus is readily installed, occupying
very little room and allowing of various combinations of
the different parts.
5. Its manipulation is of the simplest nature.
6. The apparatus has no valve in contact with the sul-
phurous acid ; the injector is constructed of special metal,
proof against deterioration due to the acid gas.
7. The quantity of sulphur consumed is very small, and
no gas is allowed to escape into the factory.
Although the general advantages claimed for the Quarez apparatus
justify its extensive application in sugar countries, it is evident that
local conditions are bound to play an important part in the usefulness
of this type of sulphitation installation.
In countries like Mauritius, Natal and Louisiana, where generally
the sulphitation process occurs before tempering, this apparatus is
Generating Plants. 15
not infrequently applied with satisfactory results. In this case it
is evident that the accuracy with which the sulphitating operation
is conducted need not be a great factor, for the degree of acidity of
the mill juice may be conveniently brought back to neutrality by the
subsequent process of liming.
On the other hand, where the "liming before sulphitation " process
is adopted in cane sugar factories, the installation in question is
much less suitable. Owing to the continuous method of sulphitation,
it becomes a more delicate problem to control the saturation of limed
juices, to give a constant neutrality of the sulphitated juice. This
is especially so in the case where several cane varieties, producing
juices of considerably fluctuating composition, are daily passed
through the mills. Therefore in Java, for instance, the Quarez
plant is rarely met with.
In beet sugar countries the case is different. On the European
continent, particularly in France, the Quarez is frequently employed.
Here, however, we are dealing with beet juices, the constitutional
properties of which are quite different from those of cane juices.
Moreover, in beet sugar factories sulphurous acid is generally applied
as an additional agent to carbonic acid.
Apparatus as used in Java, etc. — Among the most successful
and best sulphurous acid gas-producing plants is the combination
shown in Fig 3.1
This system is almost universally met with in plantation white
sugar factories in Java, and has always maintained a superiority
over others.
Its composition and operation are as follows : —
The sulphurous acid gas is generated in an oval-shaped, cast-iron
furnace E, provided with a water-cooling jacket, in order to diminish
the combustion temperature.
The required charge of sulphur is placed on an internal sliding
tray, which is thrust into the furnace after the sulphur is ignited.
Further additions of sulphur are afterwards made by way of the
feed hopper cast on the top part of the furnace, and provided with
a butterfly valve.
xAs supplied by The Sugar Machinery Manufacturing Co., Ltd., London.
16
Generating Plants. 17
The air necessary for the combustion is drawn by the air
compressor C through an air dryer B, consisting of a mild steel
chamber, fitted with a number of perforated pull-out trays or
drawers, each carrying a layer of unslaked lime, which serves to
absorb the moisture of the air.
The compressor pumps the dried air into a receiver D, whence
it enters the furnace. In this manner the formation of sulphuric
acid owing to the presence of humid air is avoided, and any desired
air pressure maintained.
The air passing across the sulphur tray carries the fumes into
the outlet pipe, which owing to its length and enlarged form and
water-cooling jacket F, acts as a sublimator, and thence into the
gas purifier and cooler G before reaching the sulphitation vessels AA.
This combined apparatus G consists of a cylindrical cast iron
vessel, containing several layers of coke or other suitable filtering
substance (pumice stone, etc.). This vessel is supported in a
tank, the open space between the two vessels being kept full of
water, constantly flowing in at the bottom and out at the top. The
gas passes down an internal pipe into the bottom of the inner vessel,
and rises through the layers of coke to the top, whence it passes on
to the sulphitation tanks, the water jacket cooling the hot gas during
its passage through the gas purifier.
It is evident that the saturation gas generated by such an in-
stallation is of a very pure nature, owing to the many precautionary
measures taken, including drying the air, retaining unburnt sulphur
particles, cooling and purifying the gas.
Though at first sight the installation described above may appear
rather complicated, its manipulation is very simple, and requires
only one man of ordinary skill to effect its satisfactory working.
Sulphitation Vessels.
The sulphitation of the juice is performed in several ways.
Sulphur Box.— One of these methods, frequently employed in
Mauritius, Natal, etc., is the use of what is known as a " Sulphur
Box." (Fig. 4).
18
Chapter III.
This consists of a vertical rectangular wooden chamber C, of
suitable dimensions, varying greatly according to the special re-
quirements in different localities. The height of this tower ranges
from 8 ft. to 12 ft. At intervals within the tower, horizontal or
slanting perforated partitions or similar devices for the purpose of
distributing the juice are fitted.
THE
FIG. 4.
SULPHUR Box."
The juice enters at the top of the tower 4 and gravitates as a
fine shower, being broken up as much as possible by the partitions,
whilst the sulphurous acid gas enters the box at the bottom 2, either
under suction or pressure promoted by a steam jet 3 suitably
arranged. After thoroughly intermixing with the gas in its downward
Plate I
Tut SUGAR MACHINERY f^ANUf
LONDON.
MODERN SULPHUR FURNACES.
Plate II
SULPHITATION VESSELS WITH STIRRING GEAR.
Sulphitation Vessels. 19
passage, the juice leaves the box at the bottom 5. A is the sulphur
furnace, and B the cooler, or sublimator.
Sulphitation Tanks. — Another method consists of the application
of an ordinary tank, provided with an agitating device and gas dis-
tributing pipes. The juice is allowed to run continuously through
the tank, in which it comes into contact with the saturation gas.
It is obvious that, though both the above methods of operation
are simple and quick, the}* do not allow of an accurate control of the
Sulphitation process. In factories where the Sulphitation precedes
the liming of the juice, however, these appliances have proved to
be satisfactory.
A very suitable and effective Sulphitation vessel, most usually
met with in the leading cane sugar countries, is shown on
Plate II,1 and described below.
It consists of a cylindrical mild steel vessel about 5 ft. 6 in.
in diameter and 9 ft. high, with a closed top having a round opening
and sliding cover for cleaning and similar purposes, and a chimney for
carrying the waste gas outside the factory.
The Sulphitation vessel is fitted with copper heating coils and an
agitating arrangement.
The saturation gas enters at the bottom of the vessel through
either perforated iron tubes or a so-called " spider web," its supply
being regulated by means of a valve worked from the staging.
The juice entrance occurs in the above illustration through a
separate valve ; in other designs it is arranged that juice and
gas enter the vessel through a common pipe, with a view to
promoting the intermixing process. Further accessories, such as
manhole, test cocks, gauge glass, sight glass, thermometer, etc.,
are usually supplied.
The Sulphitation of syrup and molasses is readily carried out in
similar tanks.
1 Kindly supplied by The Sugar Machinery Manufacturing Co., Ltd. London.
B2
CHAPTER IV.
THE CONTROL OF THE SULPHUROUS ACID GAS
GENERATING STATION.
Quantity of Lime.— The amount of quicklime required for
drying the air cannot be pre-determined, owing to the varying
degrees of humidity in the atmosphere, as well as to the gradual
formation of a skin of slaked lime, resulting in a decrease of drying
power. For this reason, it is always advisable to place a larger
quantity of lime in the air dryer than is theoretically necessary.
The regular changing of the lime at certain intervals is also essential.
The Manipulation of the Sulphur Furnace is performed as
follows : — Different methods may be applied to start the furnace.
The requisite amount of sulphur being placed on the tray, it may
be ignited by throwing upon its surface burning sulphur wicks,
which are readily made by dipping ends of old ropes into melted
sulphur. This method, however, often produces merely local com-
bustions, so that when the door is closed and the compressor started,
it frequently happens that the flame is soon extinguished or that the
SOa production is poor.
Another mode of operation sometimes applied consists in first
melting the sulphur rolls in the tray by burning wood under it.
The advantage is that a well-distributed layer of melted sulphur is
obtained, allowing of an easy ignition.
By spraying some alcohol on the sulphur, an evenly distributed
ignition may also be attained.
Regulation of the Air Supply. — The next point which deserves
attention is the regulation of the air supply for combustion. It is
obvious that an excessive quantity of air rushing through the furnace
may either be the cause of extinguishing the flames, or producing a
gas of poor strength ; on the other hand, an insufficient supply of
air causes incomplete combustion and sublimation. By rational
regulation of the speed of the air compressor, and the air valve on
the furnace, a smooth working of the furnace is ensured.
Control of Generating Station. 21
With regard to the cooling devices, it is of great importance
that the temperature of the gas should be kept as low as possible
during its journey to the sulphitation tank. The cooling-water
supply should be regulated according to the temperature noted after
passing through the various jackets.
The piping connecting the sulphur furnace with the sulphitation
tanks should be cast iron to resist acid, and of sufficient diameter to
prevent any possible obstruction. It must be arranged with a view
to convenience of cleaning, therefore an excessive number of bends
should be avoided.
Consumption of Sulphur. — An approximate estimate of the
amount of sulphur consumed by the sulphitation process may be
arrived at by the following method of calculation :—
(l) Juice Sulphitation after Tempering. — In the event of the
tempering occurring before sulphitating the juice, let it be assumed
that 1 kg. of lime is used per 1000 litres of juice (equivalent to
about 7 litres of lime-milk of 15° Beaume), of which only 550grms.
enter into combination with the SO2, the rest (equal to 3 litres of
lime-milk of 15° Beaume) being used for the neutralization of the
original acidity of the juice.
According to the equation :
CaO + SO, = CaSOs ... (a)
56 64
64 parts of SO2 are required to neutralize 56 parts of CaO, and
further according to :
S + 02 = S02 (b)
32 32 64
for the production of 64 parts of SO2, 32 parts of sulphur are
necessary. From these equations it is seen that 56 parts of CaO
require 32 parts of S, that is, 7 parts of CaO require 4 parts of S.
Thus for the precipitation of the above-mentioned 0'55 kg. CaO
per 1000 litres of juice, - — - — = 0'314 kg. of sulphur are
necessary. Assuming that 100 parts of cane produce 90 parts of
juice, we conclude that an excess of 0'55 kg. of lime per 1000 litres
of juice involves a consumption of not more than 0*03 per cent, of
22 Chapter IV.
sulphur on the weight of cane. This calculation is naturally based
on the assumption that rational operation of the sulphitation process
takes place, entailing the use of no more SOs than is necessary for
neutralization purposes.
(2) Juice Sulphitation before Tempering. — In factories where
sulphitation precedes the tempering of the juice, the consumption of
sulphur obviously depends on the degree of acidity to which the juice
is brought. Assuming this to be 0*7 grms. SO2 per litre, and consider-
ing that according to the equation (b) 1 part of S produces 2 parts of
SOi', it follows that O35 grms. S will pnoduceO'7 grms. SC>2 per litre
of juice. Taking the above figures of 100 parts of cane giving 90
parts of juice, we again obtain a consumption of 0*03 per cent, of
sulphur on the weight of cane.
(3) Syrup Sulphitation. — The approximate quantity of sulphur
required for the sulphitation of syrup and molasses may be arrived
at in a similar way to that under (2).
It is evident that these figures are only approximate, as there are
many factors of a complicating nature, which, if taken into con-
sideration, would make a calculation impossible. These above
methods are however, sufficiently accurate for practical purposes.
CHAPTER V.
ANALYSIS OF THE SULPHUROUS ACID GAS.
In spite of the obvious advisability of occasionally analysing
the combustion gases as to their SO<> content, this operation is fre-
quently neglected. The knowledge of the purity of the gas obtained
enables one to control accordingly the air supply and regulate the
sulphitation process.
Theoretical Purity,— For the determination of the theoretical
maximum purity of sulphurous acid gas, recourse is had to the
familiar equation :
S + O-2 = SO2
which teaches that one volume of oxygen on entering into combina-
tion with sulphur gives one volume of SO->. Taking the percentage
of oxygen in the air to be 21 (the figure is actually a trifle smaller,
owing to the presence of carbonic acid and moisture), and assuming
that all existing oxygen is used for combustion, the SO2 content of
the combustion gas will then be 21 per cent., which is therefore the
theoretical maximum.
This figure is, of course, never realized in practice, an excessive
quantity of air being necessary to keep the sulphur burning; 12 to
15 per cent, of SO.> in the gas is usually considered satisfactory,
while 8 per cent, is by no means uncommon.
Methods of Analysis.— The analysis of the gas may be performed
in different ways ; for instance, employing an iodized starch solution,
through which the gas is allowed to pass until complete decoloriza-
tion has occurred. This method is an excellent one for laboratory
purposes, but less applicable on a practical scale.
A convenient method, which is usually employed in sugar factory
practice, is described in the following paragraphs.
The determination of sulphurous anhydride in the saturation gas
is based upon the same chemical process as used in connection with
the analysis of carbonic acid, namely by absorption of the gas with a
solution of caustic potash. The diminution of the volume of gars
caused by this operation indicates the quantity of SO2 present.
24 Chapter V.
Figure 5 shows the apparatus employed for this purpose, of
which the following gives a brief description.
FIG. 5.
APPARATUS FOR ANALYSING SULPHUROUS ACID GAS.
Owing to the easy solubility of sulphurous acid gas in water, the
apparatus as well as the method of application differs somewhat from
that used for analysing carbonic acid.
Analysis of Sulphurous Acid Gas. 25
It consists of a burette 1 after Stammer, provided with a scale.
The top of the burette ends in a funnel-shaped vessel 2 with a
stopper. 3 and 4 are three-way cocks, the latter of which is
connected with a bottle 5 by means of a rubber tube provided with
a pinch-cock 6. This bottle is filled with water and serves to re-
place the absorbed quantity of SO-j by water, as well as to regulate
the level for the purpose of reading.
Before proceeding to analyse the samples, the burette should be
thoroughly cleansed with alcohol or ether, and subsequently dried.
Then the cock 4 is opened, so that communication is made
between the atmosphere and the water in the bottle through the
rubber tube, and the burette is raised until the water falls below
the cock 4 when the latter is closed.
Both cocks 3 and 4 are then opened, allowing communication
between the interior of the burette and the atmosphere : tube 7 on
cock 3 is connected by means of a rubber tube with the piping
conducting the sulphurous acid gas to the sulphitation vessels, and
the gas allowed to rush through the burette, escaping through the
stem of cock 4 until all air within the burette is expelled. Cocks
3 and 4 are now closed, and the connection with the gas piping
detached.
After having filled the upper tube 2 with a solution of caustic
potash of about 1-25 density, the solution is allowed to flow into the
burette, absorbing the sulphurous acid gas. The process of absorption
may be promoted by removing the burette from its stand and shaking
it for some time in a horizontal position. The burette is subsequently
replaced in its stand, and cock 4 opened, allowing water from the
bottle to run into the burette and replace the volume of absorbed gas.
After a lapse of some ten minutes or so, the bottle is raised until
the surfaces of the liquid in the burette and in the bottle are at the
same level. The decrease of volume denotes the proportion of
sulphurous acid in the saturation gas.
CHAPTER VI.
ACTION OF SULPHUROUS ACID ON JUICES.
The methods of application of the sulphitation process with
regard to cane juice in plantation white sugar factories are twofold,
namely : —
1. After tempering the juice.
2. Before
The former is the standard method as applied in Java, while the
latter is generally in vogue in Mauritius, and is also frequently met
with in Natal and Louisiana.
Action of the Gas on Juice.— Before proceeding to discuss the
pros and cons of the different methods, however, it is necessary to
enter into a general study of the various properties and actions of
the sulphurous acid gas in connection with the cane juice.
It is an acknowledged fact that sulphurous acid gas is a purifier,
a decolorizer, a neutralizer, a reducer of viscosity, and a good
antiseptic.
.Purifying Action. — When sulphurous acid gas is applied to raw
cane juice (mill juice), the following phenomena may be observed : —
A sample of the cane juice of the typical greyish to dark green
colour is treated with sulphurous acid gas in a glass cylinder to
about 0-7 grms. SO? per litre. As soon as the sulphitation operation
ceases and the liquid is again at rest, very small particles are formed
in the juice, which however are soon transformed into voluminous
and flocculent masses of varying density. The difference of density
causes a convection, and so the heavier parts move downwards
and the lighter ones upwards. After a lapse of time, varying
according to circumstances, the settling process is completed. The
sediment which usually occupies about one quarter of the total
volume, is of a lemon-yellow to greenish-grey colour, while the juice
is less opaque and of a much lighter shade.
The precipitate is mainly composed of organic matter.
Action of Sulphurous Acid on Juices. 27
It is interesting to note here the difference between the sulphi-
tation of the cane juice by means of steam injection, and the
sulphitation by compressed air, as recently investigated by the
author.
It has been observed that by applying steam injection for the
purpose of forcing SO2 gas into the juice, more precipitate of a more
flocculent nature is obtained than when using compressed air. The
settling process occurs also more quickly in the former case. Using
compressed air the juice was sulphitated to \'2 grms. SO2 per litre ;
using steam injection, although the juice only attained an acidity of
0'7 grms. S(X> per litre, the precipitate was considerably greater than
in the former case. Evidently the steam, though a comparatively
trifling amount is required for injection purposes, has a favourable
effect on the formation of precipitate in the sulphitated juice.
Purifying Effect. — From the above it is evident that sulphurous
acid gas acts as a purifier upon raw cane juice. However, by the
subsequent addition of lime, without previous removal of the pre-
cipitate, the purifying effect of the gas is practically nullified.
Bleaching Action. — The decolorizing action of sulphurous acid
is well known, and its application in the manufacture of sugar is
universally appreciated. As previously mentioned, sulphurous acid
brought into contact with juice does not only produce a precipitate,
but in addition distinctly bleaches the liquid.
This change of colour may also be obtained by using other acids
besides sulphurous acid. It has, however, been established that
juices treated with other mineral acids, such as sulphuric or phos-
phoric acids, actually exhibit a slight improvement in colour, but
not to the same extent as that obtained by sulphurous acid. Hence,
apart from its action as a mineral acid, sulphurous acid has a
decolorizing effect due to its reducing property.
The decolorization due to the latter property, as has been described
in Chapter II, is based on the liberation of hydrogen, which reduces
the organic colouring substances, with the formation of colourless
compounds. This decolorization is but temporary, for on exposure
to the atmosphere the reduced colouring matter becomes gradually
28 Chapter VI.
oxidized by the oxygen of the air, causing the juice ultimately to
assume its original colour.
By acidifying juices by means of SO-2, it may be further observed
that, as long as the acidity of the juice is preserved, the decolorization
is maintained. This permanent decolorization in case of acid
solutions is chiefly attributed to the bleaching action of the sul-
phurous acid salts formed. During the different phases of
evaporation processes these sulphites check, to a greater or less
extent, any subsequent development of colouring and air oxidizing
processes. They are easily oxidized to sulphates, in which form they
are invariably found subsequently in the syrups and molasses ; for
example : —
2 CaSOs + O2 - 2 CaSO4
It is also owing to the said property that sulphites do not impart
a darker colour to glucose solutions on heating.
On subsequent neutralization of the acid juices, however, the
decolorization entirely disappears so that the juice assumes its
original colour.
Neutralizing action. — As an agent for neutralizing the alkalinity
of limed juices, the application of sulphurous acid is generally
adopted. Besides being cheap, the lime-salts of this acid are
practically insoluble in neutral or alkaline solutions.
Reducing viscosity. — Although the opinions of authorities with
regard to the alleged property of sulphurous acid of reducing the
viscosity of juices are not unanimous, in practice it is generally
accepted that such an action occurs. So far, however, numerous
experiments have failed to disclose such an influence.
Preservative action. — Another property ascribed to sulphurous
acid is a preservative action on juices. It is generally accepted
that juices and syrups are less liable to fermentation after sulphitation.
CHAPTER VII.
PRINCIPLES OF THE
APPLICATION OF SULPHITATION TO JUICE.
Having briefly dealt with the various actions of sulphurous
acid on cane juice, we can now proceed to study the principles of
juice purifying processes by means of sulphitation.
As already stated, there exist two methods of applying the
sulphurous acid gas, namely after and before tempering the juice.
(I) Sulphitation after Tempering the Juice.
According to this method the cane juice coming from the mills
is previously treated with a certain quantity of lime, a process
known as " tempering " the juice. This purifying agent being
of no less importance than sulphurous acid in the process in
question, a study of its chemical action on cane juice is obviously
indispensable.
Tempering. — The first action of lime on cane juice is to neutra-
lize the free organic acids, forming calcium organic salts. The
combined organic and inorganic acids may likewise be decomposed.
The phosphoric acid occurring in the juice will unite to form
acid calcium phosphates which are precipitated as flocculent tribasic
phosphate.
Further, lime acts upon albuminoid, gummy and pectin matters,
which are partly precipitated. The lime combines with the albumen
which was previously suspended in the juice in a gelatinous
condition. This compound is coagulated during the subsequent
treatment by the combined action of lime and heat.
With regard to the action of lime upon gummy substances, the
opinions of various authorities are divided. Dr. Maxwell1 found
some time ago that a large quantity of gum was separated by liming
in the cold. A series of experiments conducted by the present
1 Report of the Hawaiian Exp. Station, 1896.
30 Chapter VII.
author in Mauritius, supplemented by analyses carried out at the
local " Station Agronomique," gave identical results, namely, that a
distinct separation of gum was observed on allowing an adequate
amount of lime to act during a certain time on cold cane juice.
Pectin ingredients unite with lime to form insoluble as well as
soluble compounds, which latter are also precipitated to some extent
during defecation.
Colouring substances, such as anthocyan and chlorophyll, are
precipitated by sufficient tempering.
The sugar further combines with the excess of lime, dissolving
and forming saccharates, as long as the juice is not heated.
Besides gummy matter, the most obnoxious substances playing
an important part in the manufacture of white cane sugar are the
" reducing sugars," or, as they are often termed, "glucose."
Lime, like other alkaline agents, acts on the reducing sugars
in the cold, forming glucosates which are analogous to saccharates.
These compounds are unstable, and hence easily decomposed. At
lower temperatures (below 55° C.) the chief product due to the action
of lime on glucose is lactic acid, which is a comparatively stable
acid and not subject to spontaneous decomposition. At higher
temperatures, however, dark-coloured lime-salts of organic acids,
especially glucinic and saccharic acids, are formed. These lime-
salts easily decompose, forming acid substances which may cause
inversion and which moreover do not crystallize, hence they retard
evaporation and crystallization. Their viscosity is generally known
to cause considerable trouble and losses in the boiling and curing
departments.
The main actions of lime upon the various constituents of the
the cane juice, therefore, may be summarized as follows :
Lime neutralizes the free acids ; combines with albuminoid,
gummy and pectin substances, which are subsequently partly
removed ; precipitates various bark pigments and chromogens.
On the other hand, it also forms saccharates and glucosates,
depending on the temperature, the concentration both of lime and
sugars, and the duration of contact.
l4
D
X
H*
<
PQ
Principles of Application of Sulphitation. 31
It is thus evident that lime is an excellent purifying agent, and
it is therefore no wonder that its application as such to sugar juices
has been more than justified from the earliest times.
Sulphitation.— After tempering by lime in the cold, the sulphurous
acid saturation is commenced. By this treatment the greater part
of the lime compounds enter into union with the sulphurous acid to
form insoluble sulphites, which, after undergoing a heating process,
are finally precipitated and removed with other substances in the
defecators or subsiding tanks. It is evident that sulphurous acid is
used in this case simply as a neutralizing agent. The clear juice
from these tanks should be of a very light olive yellow colour, quite
transparent, devoid of the impurities in suspension which cause the
liquid to assume a turbid or less transparent appearance.
The Sulphitation is continued until neutrality is reached as
shown by the phenolphthalein test, described under " Indicators " at
the end of this chapter. If the extent of saturation were still
further carried out, over-sulphitation would occur. This would
mean the conversion of the insoluble sulphites, such as those of
calcium and potassium, into soluble bisulphites, according to the
equation : —
CaSOs -h SO-, + H20 - Ca (HSO3)2
Calcium sulphite Calcium bisulphite
The juice would consequently be rendered acid. During heating
in the juice-heaters, and especially during evaporation, these soluble
bisulphites are split up into sulphurous acid, water and insoluble
sulphite. The latter is deposited around the heating tubes of the
evaporating vessels, thus forming an incrustation which reduces
considerably the transmission of heat. The liberated sulphurous
acid passes into the condensed water of the evaporators, causing
corrosion of the tubes.
It is therefore obvious that great care should be taken to see
that the Sulphitation process is not carried too far.
(II) Sulphitation before Tempering.
This method, as stated previously, is generally adopted in
Mauritius, and is also met with in Natal and Louisiana. It is
performed in the following manner : — The cane juice from the mills is
32 Chapter VII.
directly treated with sulphurous acid gas until an acidity of from
0'8 to 1 per cent, of SO2 is reached, and after this the juice is
neutralized by means of lime.
While in Mauritius, the author fortunately had the opportunity
of investigating the advantages and disadvantages of both methods,
in the laboratory as well as in general practice, that is, in a factory
which formerly worked according to the sulphitation-before-liming
process, but which on the author's advice subsequently abandoned
it in order to introduce the reverse method. The results1 of these
investigations, later extended to Natal practice, where both methods
are in vogue, are studied in the following sections.
As we have seen, treatment of crude mill juice with sulphurous
acid gas results in the production of a precipitate and a decolorization
of the liquid. On subsequent neutralization of the acid juice, how-
ever, the greater part of the precipitate which is mainly composed
of organic matter, is re-dissolved, and simultaneously the juice
assumes its original dark colour.
We therefore conclude that the beneficial influence of the sul-
phurous acid on the cane juice, both from a purifying as well as
bleaching point of view, disappears with the subsequent liming
process, the only useful action of the SO-2 in this case being that it
renders the mill juice acid for subsequent neutralization.
It would be different if the voluminous precipitate due to the
sulphurous acid could be removed before the application of lime.
The nature of the precipitate does not allow of a practicable filtration
so that the removal involves considerable practical difficulties, but
undoubtedly it has a beneficial effect upon the ultimate quality of
the purified juice.
In Mauritius, one factory adopted this principle of removing the
precipitate due to sulphurous acid prior to the liming, and obtained
excellent results. This operation was effected in what is locally
called a " bac portal," a shallow tank divided into narrow longi-
tudinal compartments, at alternate ends of which the partitions are
cut away to a depth of about 1 in., thus allowing the juice to travel
1 The main practical results have been elaborately dealt with in an article
by the author in " Bulletin de la Societedes Chimistes de Maurice," Nov., 1911,
No. 7.
Principles of Application of Sulphitation. 33
a distance of about 200 feet, all the time depositing the suspended
precipitate.
Returning to the sulphitation-bef ore-liming process, the acidified
juice is subsequently limed to neutrality. Now, how does the
lime act under these conditions ? The juice being strongly acid,
it stands to reason that the lime will preferably enter into union
with the acid, forming insoluble sulphites, consequently the purify-
ing property of the lime is not allowed to act sufficiently before
being rendered partly ineffective by the formation of lime salts.
Comparison. — Although, in the laboratory, scarcely any external
differences can be observed in juices treated according to the two
processes, liming-sulphitation, and sulphitation-liming, this is not so
in the case of factory practice. In the above-mentioned mill, where
both methods could be applied alternately, it has been distinctly
observed that the defecated clean juice derived from the sulphitation-
before-liming process is inferior in all respects. Though the same
light-olive colour may be obtained, the juice is much less transparent.
Further, by regulating the quantities of sulphurous acid gas and
lime, this peculiar condition of the juice could not be improved.
The peculiar opaqueness of the juice (if it may be so termed) is
most probably due to gummy and pectin impurities in suspension,
which have escaped the action of the lime. To enter into fuller
details regarding this subject would be exceeding the scope of the
present work ; it will suffice to mention that experiments conducted
in both laboratory and factory all go to prove that under normal
circumstances the liming-sulphitation is superior to the reverse
method.
Only under abnormal conditions is the application of the sulphi-
tation-before-liming process justifiable, or even advisable. For
instance, in Natal, in certain seasons, the glucose content of the
"Uba" cane may rise to a proportion unheard of in other sugar
cane countries, so that the operation of sulphitating the juice prior
to tempering is obviously more advantageous for the following
reasons.
34 Chapter VII.
High Glucose Proportion. — In cane juices containing a high
percentage of reducing sugars, it is evident that the notorious action
of lime on glucose, with the regrettable consequences pointed out
previously, is readily promoted. This fact has been repeatedly
confirmed by practice in Natal.
After abnormal seasons, including prolonged droughts when juices
with excessively high glucose contents occur, and the tempering-
before-sulphitation process is adopted, it has been frequently observed
that considerable inconvenience and manufacturing losses are ex-
perienced, especially in the boiling and curing departments, the
resulting strikes being usually of an inferior quality, and requiring
an exceptionally long boiling time, whilst at the curing station the
capacity of the centrifugals is reduced, a decrease in both output
and quality of the cured sugais being observed.
Naturally under such abnormal conditions, a greater or less
quantity of viscous constituents of analogous obnoxious character-
istics are likely to occur in the juice concurrently with the glucose,
so that one is apt to attribute the above mentioned abnormalities to
these ingredients. This is obviously partly true, but nevertheless,
cases frequently occur when the cane juice is comparatively devoid of
such viscous ingredients, but rich in reducing sugars, the treatment
of which is accompanied by the above phenomena.
By applying sulphitation before tempering, it appears that the
reducing sugars are more likely to escape the detrimental action of
the lime, owing to the latter entering into immediate combination
with the sulphurous acid contained in the juice.
Dcxtran Fermentation. — Another case where the sulphitation-
liming operation may be advantageously applied is the following :—
The occurrence of micro-organisms called Leuconostoc mesen-
terioides is undoubtedly familiar to those concerned with milling
operations. Although in nearly all colonial sugar mills the cane
juice may be to a less or greater extent infected by these micro-
organisms, the extent to which Natal mills are frequently subject to
them is considerable, especially after prolonged droughts.
Principles of Application of Sulphitation. 35
These Leuconostoc mesenterioides rapidly form from sugar a
gelatinous substance, principally consisting of " dextran," which
process is accompanied by a strong formation of acetic and lactic
acids. A small deposit of this dextran is apt to grow very rapidly
in a current of alkaline juice. A notable peculiarity is that they
are among the few organisms which require an alkaline reaction as
one of the principal conditions for their propagation.
So we see that it would be inadvisable to treat juices under these
conditions with lime without an effective preventive, such as previous
heating. By sulphitating the juice prior to liming, it is likely that
the propagation of the Leuconostoc germs is checked, and conse-
quently the occurrence of dextran fermentation avoided.
Viscous Juices.— On the other hand, it is well known that one
of the peculiar characteristics of the "Uba" cane, which is the
stable variety in Natal, is the production of extremely viscous juices,
containing besides cane wax large quantities of gummy and pectin
ingredients. Although under normal seasonal conditions the cane
juices are comparatively pure, having a low percentage of glucose
and being free of Leuconostoc germs, the excessive viscosity of the
juice still remains.
The influence of these viscous substances upon the sugar solutions
in later stages of the manufacture is of a no less damaging nature •
than those dealt with above, and it stands to reason that the early
and effective elimination of such ingredients is a matter of importance.
The application of lime before sulphurous acid gas promotes a more
vigorous precipitation of these viscous constituents, and would
therefore be more advisable on this account.
From this we see that in Natal, where the cane juices are of
such a variable nature, either of the methods of sulphitation can be
advantageously applied according to the predominant condition.
Summary.— The results described in the above study, which are
fully confirmed by mill practice, show that there actually is a
difference in the resulting product obtained from the two methods of
sulphitation ; they may not be observed in the laboratory, but this
is probably owing to the small quantities of chemicals used.
36 Chapter VII.
The Control of the Sulphitation of the Juice.
The control of the purification process of the crude juice, or in
other words, the correct reaction of the juice after treatment with
both agents, lime and sulphurous acid, is of the utmost importance,
both in regard to effect on the subsequent stages of the manufacture,
and the preservation of the installation and pipings.
Indicators. — Although the application of litmus paper as an
indicator is undoubtedly the easiest and simplest method of testing
the juice reaction, it must be borne in mind that apart from its
unreliability in an atmosphere contaminated with acid gases, litmus
reacts alkaline to acid sulphites, hence it is apt to make it difficult
to determine accurately when the point of neutrality of the juice has
been reached.
Phenolphthalein. — The only indicator of practical utility in
sugar factories is phenolphthalein. This indicator may be applied
in the form of air-dried paper or solution, the latter, owing to
its superiority, being almost exclusively used. The phenolphthalein
solution may be prepared according to different prescriptions, and
consequently its composition varies in the different factories.
One method of preparing this indicator solution is to dissolve
pure commercial phenolphthalein in a 90 per cent, alcohol solution,
in the proportion of 1 to 30.
Another prescription,1 which has the advantage of giving a more
sensitive indicator, is as follows :
A 2 per cent, solution of phenolphthalein in a solution of alcohol
(70 per cent.) is made, to which a few drops of dilute solution of
potassium hydroxide are added. The bottle is then well shaken, to
ensure thorough mixing. On the disappearance of the red colour,
more drops of potassium hydroxide are added, until it is observed
that the colour does not easily disappear, and that a faint coloration
of the liquid may be noticed by holding it before a sheet of white
paper. The solution is then ready to be used and should be pre-
served in closed bottles securely stoppered.
iArchief, 1908, p. 412.
Principles of Application of Sulphitation. 37
Testing for Neutrality.— The operation of testing the juice may
be described as follows : —
" The detection of the very last, very slightly pink reaction is
not always equally simple, and requires some routine. The best
way of conducting this test is to place the juice and the indicator
together on a white porcelain plate, taking care that this does not
take place in an atmosphere charged with sulphurous acid, and
always in the same proportion, the decoloration of the solution in
these extremely sensitive tests being to a certain extent dependent
upon the quantity of the indicator solution employed . . '."
" It is, therefore, desirable always to bring together the same
number of drops of the juice and the same number of drops of the
indicator solution ; for instance, three drops of juice and one drop of
phenolphthalein . . . Other methods favoured in factories consist
in placing a small quantity of the juice at the bottom of a porcelain
dish when a few drops of neutral phenolphthalein solution are
added ; or in placing a single drop of juice by means of a glass rod
on paper freshly moistened with the solution."
" Plantation White Sugar Manufacture," Harloff & Schmidt, p. 86.
CHAPTER VIII.
SULPHITATION OF THE SYRUP AND OF
MOLASSES.
The clear olive-yellow juice, on undergoing the concentration
process in the evaporating installation, is converted into a turbid
'dark-coloured syrup. This change of colour invariably occurs
during the concentration, so that even the best treated and clearest
juices are bound to assume a darker colour on leaving the evapor-
ation plant.
In order to manufacture plantation white sugar, it is imperative
that the colour of the solution in which the crystallization of the
sugar takes place should be as light as possible, for obvious reasons.
Thus besides the usual mechanical treatment of the syrup, con-
sisting of the removal of impurities (which owing to the degree of
concentration have not sufficient water to keep them in solution, and
which have to be removed either by filtering or settling processes),
it is manifest that the syrup requires to be decolorized prior to
entering the vacuum pans.
Decolorizing Agents. — For this purpose various chemicals are
used, including sulphurous acid, sodium acid phosphate, sodium
hydrosulphite, etc.
Generally the application of sulphurous acid is preferred, owing
to its cheapness and its powerful bleaching property. It is also
usual to employ, in addition to the sulphurous acid, one of the other
mentioned chemicals.
The sulphurous acid causes decolorization in two ways, as we
have already noted. Firstly decolorization occurs from the reducing
and consequent bleaching action of the sulphurous acid, and secondly
it arises from the acid reaction imparted to the syrup, a decolorization
engendered not only by SOi> but by any acid more powerful than
the organic acids present in the juice.
Sulphitation Operation.— The sulphitation of the concentrated
juice or syrup may be conducted according to the intermittent" or
the "continuous" method.
Sulphitation of Syrup and Molasses. 39
Apparatus for Intermittent Sulphitation.— For the first mode of
operation similar vessels to those dealt with in the chapter regarding
thin-juice Sulphitation may be suitably applied. The main advantage
of these vessels is that .they allow of an effective control of the
Sulphitation process. A simpler and more convenient method is
undoubtedly the continuous Sulphitation process. It may be carried
out in an ordinary cylindrical vessel provided with a mixing arrange-
ment or better in the following apparatus.1
Continuous Sulphitation Apparatus. — "The continuous sul-
phuring process of concentrated juice is effected by means of two
saturation tanks. In the first tank the filtered concentrated juice is
roughly sulphured to just below the required point for the maximum
bleaching, wrhile but little sulphurous acid is admitted to the second
tank in order clearly and easily to observe the final reactions.
'' The supply of sulphurous acid to the first tank may remain
unaltered, while the supply stop-cock of the second is turned on or
off according to requirement. In both tanks of course the juice
should be admitted from below, and run off at about the same level.
From the second tank it simply runs to the syrup supply tanks."
The Sulphitation process generally occurs after the mechanical
treatment of the syrup, viz., elimination and either settling or
filtration, as for obvious reasons it is inadvisable to allow the syrup
to stand with a strong sulphurous acid reaction longer than is
necessary, or to raise its temperature above 65° C.
The Control of the Sulphitation of Syrup.
The extent of Sulphitation to which the concentrated juice is
subjected varies considerably in different factories and countries.
In some factories the colour of the acidified syrup is taken as a
basis to indicate the extent of the Sulphitation. In this case a
sample of decolorized syrup acts as guide to the man in charge of
the station.
Other factories, again, adopt litmus paper as an indicator, and
conduct the sulphitating operation until a faint acid reaction is.
attained.
1 " Plantation White Sugar Manufacture." Harloff & Schmidt, p. 109.
40 Chapter VIII.
A practice much favoured in the manufacture of white sugar is
to treat the syrup with sulphurous acid gas to an acidity of 1 to
1-4 grms. of SOa (and sulphites) per litre.
Determination of Extent of Sulphitation. — For the purpose
of controlling the sulphitation of syrup, the ordinary iodometric
determination of sulphurous acid and its compounds is generally
adopted.
The iodometric titration is based upon the oxidation of sulphurous
acid and its salts by free iodine to sulphuric acid and sulphates. As
indicator for this titration, a solution of starch is used, which on
combining with free iodine to give starch iodide, assumes a blue
colour. Thus by dropping the iodine solution into the acidified
syrup, to which a little starch solution has previously been added,
the blue coloration which is formed will disappear, at first quickly,
but towards the end more slowly, until all the sulphurous acid and
sulphites are converted, when further free iodine will form starch
iodide, which causes the blue colour to be of a more permanent
character.
Standard Iodine Solution. — With a view to simplicity in read-
ing the degree of acidity, the iodine solution may be prepared as
follows : —
Assume the acidity to which the syrup is to be sulphitated to
be 1 grin, of SOj per litre. In using 10 c.c. of syrup for the titration
it follows that these 10 c.c. correspond to 10 mgrms. of SOa.
Further, according to the proportion :
127 iodine are equivalent to 32 SO.-
or (approximately) 4 iodine ,, 1 SOa
we find that in preparing a solution of 4 mgrms. of iodine to the c.c.,
one c.c. of the iodine solution used for the titration indicates 1 mgrm.
of SOa. Flence to test the sulphitation of 10 c.c. of syrup to an
.acidity of 1 grm. of SOz per litre (or 10 mgrm. of SOa for the 10 c.c. of
syrup), 10 c.c. of the iodine solution are required, and similarly, for an
.acidity of 1-4 grms. of SO^ per litre, 14 c.c. of the solution. We
thus see that the number of cubic centimetres of the iodine solution
used is ten times the number of grms. of SO? per litre of syrup.
It is obvious that this arrangement considerably facilitates the
reading of the titration.
Sulphitation of Syrup and Molasses. 41
The solution itself is prepared by dissolving 4 grms. of iodine in
a solution of about 7 grms. of potassium iodide dissolved in water,
and making the liquid up to 1000 c.c.
Iodine Titration Apparatus.— Taking into consideration the fact
that this process of titration in tropical cane sugar factories is usually
FIG. 6.
IODINE TITRATION APPARATUS.
entrusted to an Asiatic man-in-charge, and further that it is of im-
portance that the operation should be conducted rapidly, it is evident
that a practical and simple apparatus for this purpose should be
.adopted.
42 Chapter VIII.
A description of such an apparatus (Fig. 6) is as follows : —
The principal parts of the arrangement consist of a burette 1,
a Wulff's bottle 2 containing the iodine solution, and a wider
burette 3 filled with the starch solution. The connection between
the first burette and the bottle is made by a syphon arrangement.
A rubber cork carries a bent piece of glass tubing, the longer end of
which reaches the bottom of the bottle, while the other end is melted
into the wall of the burette, in such a manner that its mouth is on
the same level as the zero mark.
By pressing the rubber ball 4 the iodine solution is forced
through the glass tube into the burette, which is filled to a point a
little above the zero mark. On releasing the rubber ball, the excess
of the solution syphons back into the reservoir, leaving the burette
filled exactly to the zero mark. The burette, which is generally
graduated to one-tenth of a c.c., has a capacity to suit the circum-
stances. The regulation of the discharge of the titration liquid is
effected either by a glass cock fixed on the burette or by a pinch cock
acting on a rubber tube connecting the lower end of the burette
with a pointed glass mouthpiece.
Method of Titration. — The process of titration may be carried
out in an ordinary test tube, wrhich is provided with a mark indi-
cating a capacity of 10 c.c. The tube is filled to the mark with the
syrup to be tested, to which a small quantity of the starch solution
is added. Subsequently, the iodine solution in the burette is allowed
to flow in small quantities into the test tube. This operation is
repeatedly interrupted in order to thoroughly agitate the liquid in
the tube. At first the blue coloration which is formed disappears
immediately, but becomes gradually more permanent. The operation
is repeated until the disappearance of the blue colour is effected only
with difficulty on shaking, the mixture, care being taken to add the
iodine solution little by little as this point is approached and then
only a drop at a time until the blue colour is finally fixed. The
number of cubic centimetres of the solution required for the
titration is read off the burette, indicating the degree of acidity
according to the scheme previously outlined.
Sulphitation of Syrup and Molasses. 43
Simple Titration, — Another method of titration, which is to be
recommended owing to its simplicity, is the following :—
As a reservoir of the iodine solution, a simple bottle provided
with a syphon, Fig. 7, is used. The titration is conducted in a
% O
FIG. 7.
SIMPLE TITRATIOX APPARATUS.
FIG. 8.
VIVIEN TUBE.
Vivien tube, (Fig. 8). After filling the tube to the zero-mark
(10 c.c.) with syrup, the same method of titration is carried out.
The reading in this case is obtained from the graduated tube.
Although the iodometric method is naturally not quite exact,
owing to the syrup containing other substances which will also be
oxidized by the iodine, it is sufficiently accurate and satisfactory for
mill practice.
44 Chapter VIII.
Sulphitation of Molasses.
Whether the sulphitation of the first molasses is justifiable or
not is a matter of opinion. Some factories apply this process,
others again find it more profitable to have recourse to other bleaching
agents, such as sodium phosphate or sodium hydrosulphite.
The question of the sulphitation of molasses should be decided
in each particular case. This may be done by laboratory experi-
ments, namely by sulphitating a sample of molasses and examining
the result.
In case this decolorization process is adopted, it is impera-
tive that the molasses should be diluted prior to the operation,
to approximately the concentration of the syrup. Mechanical
treatment of the molasses, as in the case of the syrup, should
precede the sulphitation process. The control of the operation is
conducted in exactly the same way as with the syrup.
Inversion in Syrup.
Sulphurous Acid and Inversion. — It is a well-known fact that
at a high temperature the action of sulphurous acid gas on pure
sugar solutions is of an inverting character. However, it is equally
established that in the case of cane (or beet) iuices, which contain a
certain quantity of organic salts, this inverting influence of the SO-2 is
exerted to a much smaller extent. Thus the organic salts present in the
syrup have a beneficial influence in checking the process of inversion.
This property is attributed to the fact that these organic salts
combine with the sulphurous acid and sulphuric acid occuring in the
syrup, forming sulphites and sulphates, and liberating organic acids.
Hence, the free mineral acids previously existing in the syrup are
replaced by weak organic acids, the inverting power of which is
considerably less.
Not only is the inversion process dependent upon the tempera-
ture, but also on the conditions under which the heating operation is
performed. For instance, there is an appreciable difference between
the results obtained from heating the sulphitated syrup at say 70° C,
"in air" and "in vacuo."
Sulphitation of Syrup and Molasses. 45
In the first case the acidity of the syrup scarcely diminishes,
and the sulphurous acid (obviously occurring in the form of
H2 SO3) is apt to be oxidized by the oxygen of the air forming
sulphuric acid. In the second case, however, this process is not
likely to occur, for these reasons :
1. The acid reaction of the syrup in the vacuum pan diminishes
rapidly with the volatilization of the free sulphurous acid and the
organic acid?.
2. The quantity of oxygen occurring in the pan is insufficient
for the above-mentioned process of oxidation.
\Ye thus conclude that, provided the treatment of the syrup in
the sulphitation station is rationally conducted, no fear of extensive
inversion need be entertained, though the syrup is strongly acid.
Conditions to be observed, — For the rational treatment of the
syrup, the following points should be borne in mind.
1. The sulphitation operation should be carried out after the
mechanical treatment (filtering or settling) of the syrup.
2. The syrup to be sulphured should not be at a temperature
above 65° C, and if previous filtration is applied the syrup should
be cooled down to this temperature.
3. The time between the end of the sulphitation process and
the drawing of the acid syrup into the vacuum pans should be as
short as possible.
4. All pipings through which acid syrup is to run should be
made preferably of copper, and all reception tanks for acidified
syrup should be provided with a coating of acid-proof paint.
The last point, of course, has nothing to do with inversion, but
is a preventive measure against the contamination of the syrup
with iron compounds, which impart a greyish colour to the sugar
crystals.
Corrosion in Syrup Apparatus.
The detrimental effect of corrosion, which invariably occurs to a
greater or less extent when strongly acid syrups are dealt with in the
vacuum pans, is familiar to those concerned with the manufacture
of white sugar.
46 Chapter VIII.
Daring the boiling process, volatile organic acids and free
sulphurous acid are carried along with the vapours, so that eventu-
ally the piping conducting these vapours is bound to suffer from the
corrosive action of these acids.
In order to reduce the effect of corrosion to a minimum, it is
advisable to coat the inside of the vapour-conducting piping and
domes of the pans with a layer of ferric oxide.
Sodium Hydrosulphitc, or " Blankit."
Its Use in Syrup Bleaching. — Since this subject belongs to the
category of salts of sulphur acids, the treatment of this compound is
within the scope of this work.
Blankit is the pure sodium salt of hydrosulphurous acid
(Na2 SzO-i) and comes into the market as a white powder, readily
soluble in water ; if protected from moisture, it will keep for an
unlimited time in any climate.
The chemical action of sodium hydrosulphite on sugar juices is
explained in two ways.1
According to the first equation, sulphurous acid gas and hydrogen
are formed thus :
1. Na2 S2O4 + H,O = Na2 SO:< + SO2 + H,
and according to the second, under the influence of temperature,
the hypothetical SO is formed, which is immediately oxidized to
SO2, thus :
2. Na2 S2O4 = Na2 SOs + SO
SO + H,0 = S02 + H2
The decolorization of the syrup by sodium hydrosulphite is
instantaneous, and in spite of the small quantity of the agent used,
the effect is striking.
Sodium hydrosulphite does not require an acid medium, but
bleaches as well in neutral or alkaline solutions. The decolori-
zation brought about by Blankit, however, is unstable, the original
colour of the decolorized juices returning on exposure to the air.
1 Deutsche Zuckerindustrie, 1908, p. 735.
Sulphitation of Syrup and Molasses. 47
For this reason the agent should be applied at as late a stage
of the manufacture as possible, viz., in the vacuum pan, shortly
before graining.
A further advantage attributed to Blankit is that it diminishes
the viscosity of the syrup or molasses.
Application, — Sodium hydrosulphite may be applied either as a
powder or in solution. The latter is obviously to be preferred, as
it tends to a thorough mixing. It must be remembered, however,
that solutions of sodium hydrosulphite cannot be kept for long, as
they lose in decolorizing power through oxidation by the air, and
must therefore always be made up fresh immediately before use.
In practice the application of Blankit is made in various ways.
One method is to add the Blankit to the concentrated juice not long
before it is boiled. Another, which is a most rational one, is to draw
a solution of Blankit into the vacuum pan before graining, and at
certain intervals during the growth of the sugar crystals.
Syrup or Molasses — Order of Application
of the different Agents.
Whether the Blankit should be applied to syrup or molasses,
or both, is an open question, and greatly depends upon individual
opinion. While in Mauritius the author conducted a series of
experiments touching this point.
Notable characteristics of Mauritian sugar are its brilliancy and
whiteness. These qualities are indispensable if the sugar is to
compete with the Natal sugar on the Cape market. Now, as the
brilliancy of the sugar is a prime factor, the investigation of this
point was one of the chief aims of the experiments.
For this purpose syrups were separately treated with the three
decolorizing agents, i.e., sulphurous acid, sodium phosphate and
sodium hydrosulphite, prior to entering the vacuum pans. The
sugars cured from the different strikes were examined as to whiteness
and brilliancy. The sugar originating from the syrup treated with
sodium hydrosulphite was by far the whitest, but at the same time
48 Chapter VIII.
the least brilliant. Its appearance was comparable with that of
snow, exceedingly white but dull. The syrup treated with sodium
acid phosphate produced the most brilliant sugar, of a satisfactory
white colour. In both cases the syrup was first sulphitated.
In the case of first molasses, on the other hand, the crystals are
so small that there is no question of brilliancy, so that the whiteness
of the sugar crystals became the prime factor. The very same
experiments were carried out with the first molasses, the superiority
of sodium hydrosulphite in this case being indisputable.
Thus we conclude that for the production of " superior plantation
white sugar " it is advisable to treat the syrups with sulphurous acid
and subsequently with sodium phosphate and the first molasses
with sodium hydrosulphite.
CHAPTER IX.
THE SULPHITATION PROCESS IN PRACTICE.
Having studied the principle of the sulphitation process as
applied to cane juice, syrup and molasses, we can now proceed to
survey the process as applied in practice, and, in the next chapter,
review "white sugar processes" in general.
General Scheme of Operation, — The usual modus operandi
adopted by numerous white sugar mills follows with slight varia
tions the course given below.
Purification of the Mill Juice, — The mill juice runs from the
mill through copper strainers into two reception tanks, used alter-
nately, in which some of the insoluble impurities are deposited by
gravity. These tanks are provided with overflows, which allow the
juice, now freed from its larger and heavier impurities, such as sand
and mud originally adhering to the cane, to discharge into a third
reception tank. It is then pumped into measuring vessels, whence
it gravitates into liming tanks. Frequently the measuring tanks
are also used for liming purposes.
Tempering. — The tempering or liming of the juice is performed
by adding a definite quantity of lime-milk to the juice, the amount
used varying considerably according to circumstances. It ranges
from about 6 to 12 litres (in exceptional cases even higher) of lime-
milk of 15° Beaume to 1000 litres of juice. The usual practice
is to use 8 litres, equivalent to 8 X 198 grms. of CaC). As it is
essential to obtain a thorough mixture of the lime-milk with the
juice, the mixing process is best carried out in U-shaped stirring
tanks fitted with a double spiral, gear-driven. The juice is then
run into a reception tank from which it is pumped into sulphitation
vessels.
50 Chapter IX.
Sulphitation. — Under continuous agitation, the juice is sulphitated
until neutrality with phenolphthalein is reached. Previous heating
of the limed juice to about 45° C (in no case beyond 50° C) will
prove beneficial.
Heating. — The sulphitated juice on leaving the sulphitation tanks
is pumped through a multi-circulation quick-speed heater, in which
the temperature of the juice is raised under pressure to about 105° C.
A usual practice is to discharge the juice into a correction heater
(Aspinall pan) provided with a steam heating device. The juice is
here "corrected" from the somewhat varying temperature prevailing
in the first heaters.
Cleaning. — It then runs by an overflow into a series of juice
settling tanks or subsiders, where it is allowed to settle. The
settling process is followed minutely by taking samples at intervals
and observing the progress of the clarification of the juice.
The clear juice is tapped off from cocks, or float cocks, at suitable
levels, and runs into a clear-juice tank, whence it is pumped into
the evaporation plant. It is advisable to filter the juice prior to its
entering the reception tank through a revolving sieve of very fine
bronze gauze.
The sediment or dirty juice is allowed to discharge into blow-up
tanks provided with a perforated copper coil, where it is diluted
and boiled by means of live steam.
After a thorough boiling, the diluted dirty juice is pumped into
a second set of settling tanks, having about one-fifth the capacity of
the first tanks, and subjected to a second thorough subsidation.
The clear juice from these second subsiders is discharged into
the same clear juice reception tank, but the sediment goes into a
second series of blow-up tanks where it is diluted and boiled, and
afterwards filtered in either filter-presses or Taylor filters. The
clear juice from these filters runs into the clear juice tank.
The 5ulphitation Process in Practice. 51
Evaporation. — "if measures have been taken for settling the
syrup, it should be borne in mind that the concentrated juice must
not be allowed to become too thick ... A proper settling is propor-
tionate to the difference which exists between the density of the
concentrated juice and that of the subsiding impurities. If this
difference is considerable, in other words, if the juice is less concen-
trated, settling will proceed much more readily, and vice versa."
" In general the impurities subside very readily and rapidly at
26° Be, but above 27'5° Be the process is less successful." 1
Treatment of the Syrup. — -The syrup is drawn from the last
vessel of the evaporating installation and discharged into eliminating
tanks and heated to boiling point. The scum formed on the
surface is carefully skimmed off, and the syrup allowed to gravitate
through special filters into cooling tanks, or discharged into a series
of syrup subsiders. The sediment in the latter case is preferably
returned to the mill, or one of the first reception tanks, slowly and
regularly, so that it may be distributed as much as possible over
large volumes of the raw juice.
At a temperature below 65° C, the syrup is subsequently sulphitated
to an acidity of I/O grm. of SOi per litre of concentrated juice and
pumped up into the vacuum pan supply tanks. An addition of sodium
hydrosulphite may be made in the tanks or in the pans at option.
Treatment of the First Molasses.
The molasses obtained on curing the first massecuites, of a purity
of 65 to 68 and a Brix of about 80°, contains all the impurities of the
massecuite in a more concentrated state, in addition to traces of iron
compounds originating from the tanks by their constant contact
with the acid syrups and molasses. A separate clarification of the
molasses is therefore to be recommended, so that all the suspended
mechanical impurities may be removed before a new crystallization
takes place. These impurities may otherwise impart a dark tint to
1 " Plantation White Sugar Manufacture." Harloff & Schmidt, p. 112.
D 2
52 Chapter IX.
the crystals of the second massecuite, and so prevent the obtaining
of a superior product. An efficient clarification of the molasses is
effected by the following method.
Clarifying the Molasses. — The molasses obtained on curing the
first massecuites is pumped into eliminators provided with perforated
steam coils. After being diluted to about 65° Brix (35'5 Be), the
molasses is thoroughly boiled. The skimming off of the scum
formed on the surface is most important and should be continually
repeated.
The further treatment of the molasses, as in the case of the
syrup, may be conducted in two ways, by (l) filtering, or (2) settling,
1. Filtering — The molasses is allowed to flow through special
filters into tanks to cool down to a temperature below 65° C., at
which temperature it is sulphitated to an acidity of 1'2 to 1'5 grms.
of SO2 per litre.
2. Settling — The molasses is discharged into subsiding tanks,
where a quantity of sodium phosphate is added. The determina-
tion of the quantity required is carried out in the laboratory, where
samples of the same molasses are treated with different quantities
of the phosphate.
After having undergone either of these treatments the molasses
is drawn into the vacuum pans. The application of sodium hydro-
sulphite in the vacuum pan will undoubtedly prove beneficial.
The quantity of Blankit obviously varies according to circum-
stances, but approximately 17 to 20 grms. of this substance to the
ton of massecuite may be applied.
Treatment of Second Molasses. — The molasses obtained on
curing the second massecuites is diluted and thoroughly boiled in
blow-up tanks, fitted with perforated copper coils. Generally a
further clarification of this molasses is not required.
Boiling.
The treatment of this subject in detail would naturally be outside
the scope of this work, hence only a summary is given in the
following section : —
In Java, two methods of manufacturing white sugar are in
vogue. The first produces only superior first sugar and superior
The Sulphitation Process in Practice. 53
molasses sugar, while the second method consists in turning out
only superior white sugar and exhausted molasses.
By keeping the first product separate from the after-product, it
is evident that the quality of sugar is bound to be superior. There-
fore, in white sugar producing countries like Mauritius and Natal,
where the colour of the sugars is of utmost importance, the method
of obtaining the whole product in one "jet" cannot be advantageously
adopted.
The Two-sugar Method. — " In obtaining sugar in two jets, all
the thick-juice is entirely boiled to a primary massecuite in such a
manner that the "run-offs" from it shall have a purity of about 65°.
These run-off syrups are then worked up by slow boiling and lengthy
cooling to a molasses of about 33° quotient of purity."
" When the initial purity is high, the sugar is separated in three
stages, viz. (l) first sugar with a run-off of 70°; (2) superior molasses
sugar, with a run-off of 55° ; and (3) molasses sugar. This last sugar
is spun white simultaneously with the superior molasses sugar, and
mixed with it."
Single Sugar Process. — " In the method of making white sugar
and molasses, the purity of the thick-juice is continually lowered
by mixing-in the first run-off. Generally, it is best to work with a
mixture having a purity of 78°-80°, when the resulting massecuite
after machining gives a run -off of about 5S°-60° purity. As above,
the run-off is worked in one jet to molasses, obtaining so-called
' molasses sugar,' which however is not machined white as before,
but is pugged and drawn into the first sugar pans. The pugged
grain is diluted in the pans with some mixed thick-iuice, and
thus forms a 'pied-de-cuite ' [or starting grain] for the first sugar
massecuite."
" Such a first massecuite sugar consists of molasses sugar as
the primary grain, and is boiled with a mixture of syrup and thick-
juice having a purity of about 78°-80°. The remaining run-off once
again gives molasses sugar, etc." '
i " Plantation White Sugar Manufacture." Harloff & Schmidt, pp. 128 and 129.
54 Chapter IX.
For the manufacture of superior white sugar it is rational to
adopt fractional centrifugalling, by which process the " green
molasses " (impure molasses from the first set of centrifugals) is
separated from the " clear molasses " (which is an almost pure sugar
solution coming from the second set of centrifugals). The clear
molasses is pumped either directly into the concentrated juice tanks
or into special tanks, whence it is drawn into the pans separately.
The green molasses is treated as explained previously.
Blueing the Sugars.
In order to neutralize the last traces of yellow tint on the
•crystals, it is a usual practice to blue the superior sugars with a
solution of either ultramarine or indanthrene in the centrifugals.
'When employing this method, it is essential that the solution shall
not contain large particles of the blueing substance in suspension.
CHAPTER X.
PROCESSES ADOPTED BY THE LEADING WHITE
SUGAR COUNTRIES*
After studying a general scheme of white sugar manufacture,
we can now proceed to deal with the main processes as applied in
the three leading white sugar countries, viz., Java, Mauritius and
Natal.
I. Java.
The scheme described in the previous chapter may be taken as
the standard method of white sugar manufacture according to the
sulphitation process in Java.
The Bach Treatment of Syrup. — Recently, however, a new
process of treating the concentrated juice has been introduced by
Bach, and has given satisfactory results. The mode of operation
may be described as follows : —
The syrup is drawn from the last vessel of the evaporation plant,
and pumped through a syrup-cooler. The cooled syrup is discharged
into a series of first sulphitation vessels, where it is first treated with
lime until a distinct alkaline reaction is reached, and the limed syrup
subsequently sulphitated to neutrality. It then runs into eliminating
pans, where it is heated to boiling point, the scum formed on the
surface of the liquid being carefully skimmed off, and eventually
the concentrated juice gravitares into a reception tank, whence it is
pumped through filter-presses.
The filtered syrup is pumped from a reception tank through a
cooler into a second set of sulphitation vessels. After being satis-
factorily bleached by the second application of the sulphurous acid
gas, the syrup is discharged into a reception tank and ultimately
pumped into the vacuum pan supply tanks, whence it is drawn into
the pans.
56 Chapter X.
II. Mauritius.
The general method of manufacturing white sugar in Mauritius
is along the following lines :
Sulphitation. — The mill juice is pumped continuously though a
sulphitation tank of the " continuous sulpnitation " type, the
sulphurous acid gas meanwhile being forced through the juice by
means of steam injection (Giffard). The acidity to which the raw
juice is generally sulphitated ranges from O8 to 1 per cent. SO2.
Liming and Measuring- — The sulphitated juice is then run into
liming tanks, in which it is measured and limed. The extent of
liming varies in different factories : usually the acid juice is limed
until only a slight acid reaction with litmus paper is obtained.
Neutral juices are met with only in a few factories, the reason being
the difficulty of obtaining an exact neutrality by means of lime. A
few other factories, again, prefer to work with slightly acid juices.
In some instances the sulphitated juice is rendered alkaline by a
surplus of lime and subsequently treated with phosphoric acid until
a slight acid reaction is reached.
Heating the Juice. — The juice is pumped through a series of
heaters, being usually heated to 70°-75° C. In a number of
factories the juice, after being heated, is allowed to run through
a " bac portal" (described in Chapter VII), in which it deposits
part of its impurities. This apparatus is gradually becoming,
however, less popular, and a great number of factories have
discarded it.
Defecation, — From the " bac portal " the juice either runs or is
pumped into defecators, provided with heating coils or double
bottoms. It is heated to boiling point, in other words until the
layer of scum formed on the surface begins to burst (cracking
point), when the juice is allowed to settle.
Filtering,- — The clear juice gravitates through a series of Danek
filters, or in some cases through a sieve of fine gauze into a recep-
tion tank.
Leading Processes. 57
The sediment of the defecators is discharged into blow-up tanks,
where it is thoroughly boiled, and afterwards pumped through filter-
presses, from which the filtered juice runs into the same reception
tank.
Evaporation and Treatment with Phosphate, — This clear juice
is pumped into the evaporation plant and is concentrated to about
26°-28° Beaume. The syrup is discharged into settling tanks of
ample capacity, where it is treated with phosphoric acid (in the
form of calcium superphosphate containing 43~45 per cent, of
phosphoric acid). The amount of phosphate applied varies, ranging
from 1 to 1*5 grms. (in some cases even 2 grms.) of superphosphate
per litre of syrup.
Subsiding. — As this agent not only decolorizes the syrup, but
also produces an appreciable precipitate, it is evident that sufficient
time should be allowed for settling ; according to the settling capacity
at the factory's disposal, the period ranges from 10 to 24 hours. The
degree of concentration and the temperature of the syrup are of course
factors to be taken into consideration in deciding the period of the
settling process.
Sometimes the syrup from the evaporating installation is further
heated to boiling point and " eliminated " prior to undergoing the
settling process. After the settling is completed, the sediment in the
syrup subsiders is usually discharged into the juice defecators.
Boiling. — The clear concentrated juice is then drawn into the
vacuum pans. Often sodium hydrosulphite is applied to the syrup
either just before entering the pans or during the boiling.
As pointed out previously, the quality of the sugar in Mauritius
is mainly estimated on the colour of the product. Under these
circumstances it is not surprising that the process of drawing in
of molasses in head boilings " to recover as much superior white
sugar as possible, is not favoured there.
The method generally adopted on that island is to produce ' first
sugars " from syrup and " second sugars " from first molasses (both
of a superior white colour) without utilizing the " drawing in "
process. Further low grade sugars of an inferior colour are also
produced.
58 Chapter X.
Molasses. — The molasses is treated in a manner previously
described. It is thoroughly boiled in blow-up tanks and the
lighter impurities carefully skimmed off. A certain quantity of
phosphoric acid is added, and the molasses allowed to settle for a
considerable time, the length of which depends upon circumstances.
Sodium hydrosulphite is also frequently applied in the pans,
when boiling first molasses.
The crystallization and curing processes in the larger factories
are usually carried out according to the methods now universally
adopted.
III. Natal.
The manufacture of white sugar in this country is almost on the
same lines as that in Mauritius. The following main differences,
however, may be noted : —
Wax Separation.— Owing to the fact that the Natal juices (from
" Uba " cane) generally contain excessive quantities of wax and
other viscous substances, the limed and sulphitated juice is pumped
into a series of defecators, better called -" wrax separators."
The majority of factories use the ordinary type of French defe-
cators for this purpose, and follow the usual defecation process.
A more rational mode of operation now employed in several
factories consists of allowing the juice to run through ' continuous
wax separators " composed of three or four defecators connected to
one another. The juice runs slowly through the consecutive defe-
cators, while the waxy matter rises to the surface to form a thick
layer of scum, which is removed at frequent intervals. The
temperature of the juice is kept below 82° C, as the wax melts at
about that temperature, and the regulation of the temperature
requires careful attention.
The clear juice running out from the last vessel is pumped
through quick-speed heaters and its temperature raised to boiling
point, when it gravitates into subsiding tanks and subsequently
undergoes the same process as applied in Mauritius.
SUMMARY.
In conclusion, it may be useful to give a summary of the
observations and conclusions arrived at in our study of the sul-
phitation process and the manufacture of "superior white sugar"
according to that process. For convenience and facility of
reference this can be done in the form of a series of questions
and answers.
Tempering.
1. In what form is the lime
added to the iuice ?
2. Which form is preferable,
and for what reasons ?
3. What quantity of lime-
milk is used ?
4. How is the quantity of
lime-milk determined ?
1. As powdered quicklime, or a
lime-milk.
2. Lime-milk, as it conduces to
thorough mixing. Unslaked
lime is slaked incompletely in
cold juice and is apt to form
hard nodules covered with a
sticky layer of impurities,
which subsequently affect the
quality of the juice.
3. Usually 8 litres of lime-milk of
15° Beaume per 1000 litres
of juice. This figure varies
considerably, and may range
from 6 to 12 litres.
4. (a) In the laboratory by deter-
mining how many c.cs. of
lime-milk are necessary to
obtain a complete precipita-
tion in one litre of juice.
(b) The following method is
preferable : Add a certain
quantity of lime-milk to the
mill juice and treat the latter
60
Summary.
5. Where and how is the
juice to be treated with
lime ?
6. What form of agitating
tank is most suitable ?
7. At what temperature
should the tempering
process be carried out ?
in the factory according to the
usual practice. A sample of
the defecated juice is examined
in the laboratory with a few
drops of a solution of calcium
saccharate. The formation of
a precipitate indicates insuffi-
cient application of lime to the
juice. The amount of lime-
milk added to the mill juice is
gradually increased until no
further precipitate is obtained
in the laboratory test. The
absence of a precipitate in the
first experiment shows that
either the exact quantity or an
excess of lime-milk has been
applied : the regulation of the
tempering should be performed
accordingly.
5. Preferably in special liming
tanks under constant agitation.
Another practice is to temper
the juice in the measuring
tank, whence it is discharged
into limed juice stirring tanks.
6. Horizontal U-shaped tanks,
provided with a double spiral,
mechanically driven. Vertical
tanks have been proved to
allow the settling of lime at
the bottom.
7. The temperature should prefer-
ably be kept low, say about
30°-35° C.
Summary.
61
Is it beneficial to heat
the limed juice prior
to sulphitation ?
9. What is the action of lime
on the juice ?
8. The heating of the limed juice
immediately before sulphita-
tion has given satisfactory
results. The rise of tempera-
ture increases the energy of the
liming action from the chemical
point of view, so that gummy
and pectin matters will be more
readily precipitated. This is
best done in the sulphitation
vessels, which should be pro-
vided with heating coils. The
resulting temperature should
not exceed 50° C.
9. It neutralizes the free acids oc-
.curring in the juice, acts on
albuminoid, gummy and pectin
substances, which are subse-
quently partly removed, pre-
cipitates various bark pigments
and chromogens and forms
saccharates and glucosates.
Preparation of Lime-milk,
10. What are the qualities
of the lime to be used ?
10. The lime should be of the purest
and best kind available, contain-
ing as little impurity as possible.
The maximum of magnesia in
the lime allowable is 2 per
cent. If over-burned, the lime
becomes rocky and slakes with
difficulty, so that it loses its
efficiency. The lime should
not contain any unburned par-
ticles, as these cause trouble.
62
Summary.
11. Of what nature should
the lime-milk be ?
11. The lime-milk should be homo-
geneous and void of hard
particles of lime, which are
apt to escape the action of
the sulphurous acid and
afterwards gradually dissolve,
imparting an alkaline reaction
to the juice.
It is therefore essential that
the lime should be thoroughly
powdered and slaked.
Sulphitation of the Juice.
12. What form of sulphi-
tation vessel is to be
preferred ?
13. How is the distribution
of the saturation gas
performed ?
14. How can the mixing
process of the juice and
the gas be assisted ?
12. Vertical cylindrical vessels,
provided with heating coils,
agitating device, gas distri-
buting piping and further
accessories, such as gauge
glasses, test cocks, thermo-
meters, etc.
13. Either by means of perforated
pipes or by so-called " spider
webs." The efficiency of the
SO 2 gas is obviously dependent
upon the thoroughness of its
distribution and also upon
the height of the juice to be
treated. Hence these points
should be taken into con-
sideration when designing a
sulphitation vessel.
14. By continuous agitation of the
juice during the sulphitating
operation and also by allowing
the juice and gas to enter
into the tank through a com-
mon pipe.
Summary.
63
15. How is the sulphitation
process controlled ?
16. How is the phenol-
phthalein solution
prepared ?
17. How is the indicator
solution applied ?
18. To what extent is the
sulphitation process
carried out ?
19. What occurs if the sul-
phitation is further
extended ?
15. By the use of indicators, usually
litmus or phenolphthalein, in
the form of sensitized paper or
solution. The phenolphthalein
solution is preferable.
A supplementary control of
the sulphitation process may
be advantageously carried out
" by sight," that is, by follow-
ing the course of sulphitation
and taking samples at intervals,
also observing the process of
settling.
16. By dissolving phenolphthalein
in a 90 per cent, alcohol solu-
tion, in the proportion of 1
to 30.
17. By adding to a few drops of
juice in a white porcelain dish
one or two drops of the phenol-
phthalein solution, or by plac-
ing a single drop of the juice
by means of a glass rod on
paper freshly moistened with
the solution.
18. Until the indicator solution
assumes only a faint pink
coloration, instead of a deep
crimson.
19. " Over-sulphitation," which
renders the juice acid and
causes the formation of soluble
bisulphites, which are subse-
quently decomposed in the
evaporators into insoluble
sulphites and free sulphurous
acid.
Summary.
20. To what is incrustation
and corrosion attributed ?
21. How does
occur?
inversion
22. For what purpose is the
sulphurous acid gas
used ?
20. Chiefly to the above-mentioned
decomposition. The sulphites
form incrustations on the tubes
of the calandrias, while the
liberated sulphurous acid is
converted into sulphuric acid
which exerts its corrosive
properties. Free sulphurous
acid is also produced by
volatilization.
21. When acid juices are subjected
to high temperatures inversion
takes place.
22. In the case of limed juices,
SOo is chiefly used as neutral -
izer.
Generation of Sulphurous Acid.
23. In what form is the sul-
phurous acid used ?
24. How is it obtained ?
25. What is the most suit-
able installation for the
production of SO^ ?
26. WThat are its advantages
over other plants ?
27. What is the usual pro-
portion of SO 2 in the
combustion gas ?
23. In cane sugar factories almost
exclusively in the gaseous
form.
24. By the simple combustion of
sulphur in air ;
S + Oo - S02
25. The combination showrn in Fig.
3, Chapter III, composed of
air-drier, air-compressor, air-
recipient, sulphur furnace, gas
purifier and cooler.
26. Mainly the generation of very
pure saturation gas, and an easy
control of the operation.
27. This figure varies considerably,
but 15 per cent, is satisfactory.
Summary.
65
28. What are the main
points to be borne in
mind in the generation
of SO2 ?
29. How are the precau-
tionary measures to be
carried out ?
28. (a) Dry air for combustion.
(b) Air supply to be regular.
(c) Combustion temperature in
the furnace to be kept as low
as possible.
(d) Uniform combustion of the
sulphur layer in the furnace.
(e) Sublimation in the pipings
to be checked as much as
possible.
(/) The temperature of the satu-
ration gas to be kept low.
(g) The gas to be purified be-
fore entering the sulphitation
vessels.
29. (a) By drawing the air through
an air dryer, composed of
several layers of quicklime.
(b) By using an air-recipient
and regulating valves.
(c) By cooling the furnace by
means of continuously running
water.
(d) By melting the sulphur rolls
in the furnace by previous
heating of the tray, as ex-
plained in Chapter IV.
(e) By cooling, and the pro-
vision of sublimators.
(/) By constant cooling of the
gas by means of water-jackets.
(g) By filtering the gas through
coke or pumice stone, and
washing to absorb free SO8.
66
Summary.
Treatment of the Syrup and Molasses.
30. Howis thesyrup treated
prior to sulphitation ?
31. How is the sulphitation
carried out ?
32. How is the sulphitation
of the syrup controlled ?
33. How is a standard
iodine solution pre-
pared ?
34. How is the titration
carried out with the
iodine solution ?
35. What is the action of
SO:> on syrup ?
30. The syrup is heated to boiling
point, eliminated, and either
filtered or settled. If filtering
is employed, subsequent cool-
ing of the syrup is necessary.
31. The syrup is pumped up into
sulphitation vessels and treated
with sulphurous acid gas until
an acidity of 1 to T2 grms. of
SO 2 per litre is obtained.
32. By means of an iodine solution,
with a starch solution as indi-
cator.
33. By dissolving 4 grms. of iodine
and about 7 grms. of potassium
iodide in 1 litre of water.
34. 10 c.c. of syrup are diluted with
water, a little of the starch
solution added, and subse-
quently titrated with the iodine
solution. Each c.c. of the
standard iodine solution in-
dicates 1-0 mgrm. SOa.
35. The action of SOa on syrup
is fourfold, namely :
(a) It reduces the organic colour-
ing substances occurring in the
syrup to colourless compounds.
The bleaching effect due to this
phenomenon is, however, only
of a temporary nature, as by
N oxidation the original dark
colour of the syrup gradually
returns.
Summary.
67
36. How does the question
of inversion enter here ?
37. At what temperature is
the sulphitation process
to take place ?
38. How is the molasses
treated ?
(b) It imparts an acid reaction
to the syrup, by which a
decolorization is caused. This
decolorization is preserved so
long as the syrup remainaacid.
(c) It exercises a purifying in-
fluence, as it decomposes part
of the non-sugars, which may
be removed eventually.
(d) It further acts as a preser-
vative of the syrup.
36. Although the syrup has a dis-
tinctly acid reaction, a rational
treatment of the syrup after
sulphitation precludes inver-
sion to any extent.
37. It is advisable not to allow the
temperature of acid syrups to
exceed 65° C in the atmos-
phere. A rise in the tempera-
ture in the vacuum pans is of
no consequence, as already
pointed out.
38. The first molasses is diluted
to about the density of the
syrup, and subsequently treated
in the same way as the syrup.
The application of additional
bleaching agents, such as
phosphates or sodium hydro-
sulphites may prove to be
advantageous.
K 2.
INDEX
PAGE
Acetic acid in juice . . . . 35
Achard's sulphuric acid
process . . . . . . 1
Acid juice 31, 56
Acid syrup . . 38, 39, 45, 51, 66, 67
Acidity of molasses . . . . 52
Acids, Organic 29, 46
Agitating tanks 49, 60
Air compressor. . .. .. 17
Air drying . . . . 8, 17, 65
Air receiver . . . . . . 17, 65
Air regulation . . . . 8, 20
Albuminoids, Action of lime on 29
Alkaline juice, Leuconostoc
germs in . . . . . . 35
Alkaline syrup . . . . . . 55
Analysis of SO.2 gas .. . . 23, 64
Anthocyan, Action of lime on 30
B
Bac portal .. .. ..32,56
Bach treatment of syrup . . 55
Baissac, Apparatus described by 10
Bassett 2
Battut 2
Berthollet 9
Bi-sulphites, Formation of . . 31, 63
Blankit 46, 48, 52
Blankit in molasses . . . . 48, 52
Blankit in vacuum pans 47, 51, 52
Bleaching agents . . 7, 27, 47, 66
Blueing the sugars r. .. 54
Boiling 52, 57
Boulon's researches . . . . 2
Brilliancy of sugar crystals . . 48
PAGE
Calcium phosphate . . . . 29, 57
Centrifugalling in Mauritius. . 58
Centrifugals, decreased capacity 34
Chlorophyll, Action of lime on 30
Chromogens, Precipitation of 30, 61
Clarification of molasses . . 52, 54
Cleaning of SO.2 gas . . . . 9, 65
Cleaning of juices . . . . 50
Colour of clear juice . . . . 31, 33
Colour of sugar 45, 47, 51, 54, 57
Colour of syrup . . . . 38, 39
Concentration, Degree of 51
Continuous sulphitation appa-
ratus 17, 39, 56
Continuous wax separators . . 58
Control of gas generating
station . . . . . . 20
Control of sulphitation of juice 36, 63
Control of sulphitation of syrup 39
Cooling the SO.2 gas . . 17. 21, 65
Cooling the syrup . . 51, 55, 66
Corrosion in apparatus 31. 45, 64
Crystals, Colour and appear-
ance of
45, 47, 51, 54, 57
D
Danek filters
Dapriez
Decolorizing agents .
Decolorizing juice
Decolorizing molasses
Decolorizing syrup
Defecation
Defecators
56
1
38
. . 7, 27
48
38, 46, 57, 67
.. 31, 56
. . 31, 56
69
Density of concentrated juice
(syrup)
Deposits on evaporator tubes
Dextran fermentation. .
Dombasle
Droughts, effect on glucose . .
Dubrunfaut
51
31
34
1
34
1
Elimination. Juice and Syrup
51, 52, 55, 57, 66
Evaporation, Degree of . . 51, 57
Exhausted molasses . . . . 53
Filter-presses ... .. .. 50,56
Filtering juice, molasses and
syrup 52, 55, 56, 66
Fractional centrifugalling
Fradiss
Free SO.2 in evaporators
Free SO2 in vacuum pans
Free SO2 in vapour pipes
Furnaces, sulphur
31,
54
2
63
45
46
15, 20, 65
Q
Gas inlets 19, 62
Gaseous sulphurous acid , . 5
Generating plants for SO,2
10, 12, 15, 64
Generation of sulphurous acid 7, 64
Glucosates 30, 61
Glucose 30, 34
Green Molasses . . . . 54
Gum, Action of lime on . . 29
Gum and pectin in juice . . 33, 35
H
PAGE
Harloff 2
Hazewinkel . . . . . . 2
Heater, Correction (Aspinal
Pan) 50
Heater, Quick-speed . . . . 50, 58
Heating of limed juice 50, 56, 61
Heating of sulphitated juice. . 50
Heating of sulphitated syrup 51, 66
Horsin-Deon . . . . . . 6
Hydrosulphite, Sodium
38, 46, 47, 48, 51, 52, 67
I
leery, Dr., Experiments of .. 2
Indanthrene . . . . . . 54
Indicators .. . .36, 39, 63, 66
Intermittent sulphitation appar-
atus 19, 39
Inversion in syrup . . 44, 64, 67
Iodine, Action of SO.2 on 7
Iodine standard solution . . 40, 66
Iodine titration apparatus 41, 43, 66
Iron contamination
45, 51
Java installations and methods
15, 26, 52, 55
Juice, Clear or subsided . . 50, 58
Juice, colour after defecating 31, 33
Juice, Concentrated, purity of 53
Juice, Heating .. .. 50, 56, 61
Juice, Neutral .. .. .. 56
Juice neutralizing by SO.2 . . 28
Juice settling 57, 58
Juice, Temperature of limed 50, 61
Juice, Temperature of sulphitated 50
Juice, Viscous . . . . 35
Juice, Wax in 35
70
PAGE
Lactic acid, Formation of .. 30, 35
Leon, description of sulphur
refining . . . . . . 3
Leuconostoc mesenterioides. . 34
Lime, Action of, on juice, etc.
29, 33, 61
Lime-Milk . . . . 49, 59, 61
Liming after sulphitatmg 32, 33, 34
Liming before sulphitating . . 29, 49
Liming, Extent of . . . . 56
Liming in measuring tanks 49, 56, 60
Liming syrup . . . . . . 55
Liquid sulphurous acid .. 5
Litmus paper . . . .36, 39, 56, 63
Louisiana, methods employed 26, 31
M
Mauritius, apparatus and
methods . . . . 10, 26, 31, 56
Mauritius Sugar . . 47, 53, 57
Maxwell, Dr. (Hawaii) .. 29
Melsen . . . . . . . . 2
Merge . . . . . . . . 2
Mill Juice, Purification of . . 49
Molasses, Dilution of.. .. 52, 67
Molasses, Drawing in of . . 53, 57
Molasses, Exhausted . . . . 52
Molasses, Eirst, Treatment of 52,57,67
Molasses, Green . . . . 54
Molasses, Purity and density of 52, 53
Molasses, Second, Treatment of 52
Molasses, sulphitating 38, 44, 52
N
Natal Juice, Leuconostoc germs in 34
Natal, Methods employed in
26, 31, 34, 53, 58
Neutral juice and syrup . . 55, 56
Neutrality, Sulphitating to . . 50, 55
Neutrality, Testing for . . 37
Organic acids . . . . . . 29
Organic salts and inversion . .
Over-sulphitation . . . . 31
Oxygen in vacuum pans
PAGK
46
44
63
45
.29, 33,
35, 61
.31, 36,
50, 63
.38, 47,
52, 67
.
29, 57
.29, 56,
57, 58
53
ng S0.2
8, 65
?
32
9
3-v a . .
26, 55
misiana
26, 31
Pectin .. ...
Phenolphthalein
Phosphate, Sodium
Phosphate, Calcium
Phosphoric acid
Pied-de-cuite . .
Precautions in generating SO.2
Precipitate, Temporary
Priestley
Process employed in Java
Process employed in Louisiana
Process employed in Mauritius
26, 31, 32, 56
Process employed in Natal . .
26, 31, 34, 58
Proust . . . . . . . . 1
Pugged sugar 53
Purifier for SO.2 gas . . . . 17
Q
Quantity of Blankit . . . . 52
Quantity of calcium super-
phosphate . . . . . . 57
Quantity of lime for air drying 20
Quantity of lime-milk . . 59
Quarez sulphitation installa-
" tion 12
Quicklime 59, 65
Reducing sugars . . . . 30 34
Reducing viscosity . . . . 28
Refining Java sulphur . . 3
/> 71
Saccharates, Formation of . . 30, 61
Schulze 2
Scum in eliminators, etc.
51, 52, 55, 56, 58
Sediment, syrup, Return of .. 51, 57
Settling, Juice 57, 58
Settling, Molasses . . . . 52, 58
Settling, Period of . . . . 57
Settling, Syrup .. 51, 57, 66
Seyferth 2
Single sugar process . . . . 53
Sodium hydrosulphite
38, 46, 47, 48, 51, 52, 67
Sodium phosphate . .38, 47, 52, 67
Starting grain . . .. . . . 53
Stolle 2
Strikes, Inferior . . . . 34
Sublimators .. .. 7, 8, 17, 65
Subsiders .. ..31, 50, 57, 58
Sugar, First superior . . . . 52, 57
Sugar, Inferior. . .. .. 57
Sugar, Molasses . . . . 53, 57
Sugar, molasses, Superior . . 52, 57
Sugar, Pugged 53
Sugar, white crystals (Mauritius)
47, 57
Sulphates, Formation of . . 44
Sulphitation after tempering 29, 49
Sulphitation before tempering 31, 33
Sulphitation, Continuous . . 39, 56
Sulphitation, Extent of
32, 39, 50, 51, 56, 63, 66
Sulphitation installation, Quarez 12
Sulphitation installation used
in Java . . . . . . 15
Sulphitation installation used
in Mauritius . . . . . . 10
Sulphitation, Intermittent .. 39
Sulphitation of molasses . . 44, 52
Sulphitation of juice, Control of
36, 50, 63
Sulphitation of syrup 38, 39, 45, 51, 55
Sulphitation process.Dombas'e 1
Sulphitation process,
Dubranfaut . . . . . . 1
Sulphitation process in practice 49
Sulphitation vessels . . 17, 39, 62
Sulphites .. 31,33,36,44,63
Sulphites', Researches with . . 1
Sulphur box . . . . . . 17
Sulphur, Consumption of 21
Sulphur, Origin, Properties,
Refining, etc. . . . . 3,4
Sulphuric acid . . 1, 6, 9, 44, 64
Sulphurous acid , action on juice 26, 66
Sulphurous acid, Cleaning of 9, 65
Sulphurous acid, Dapiiez
process . . . . . . 1
Sulphurous acid, Dissociation of 6
Sulphurous acid in evaporators 31, 64
Sulphurous acid in vacuum pans 45
Sulphurous acid in vapours . . 46
Sulphurous acid, neutralizing
action 28, 64
Sulphurous acid, Oxidation of 6
Sulphurous acid, preservative
action. . . . . . . 28
Sulphurous acid, Properties of 6
Sulphurous acid, Proust's
application . . . . . . 1
Sulphurous acid, purifying
action. . . . . . . . 26, 67
Sulphurous acid, specific
gravity . . . . . . 6
Sulphurous acid, Stolle
process . . . . . . 2
72.
PAGE
Superphosphate, Calcium . . 57
Syrup, Application of
Blankit to 47
Syrup, Bach treatment of . . 55
Syrup, Colour of . . . . 38
Syrup cooler .. .. ..55,66
Syrup, Decolorizing of 38, 46, 57
Syrup, Double sulphitation of 56
Syrup elimination . . . . 57, 66
Syrup filtering . . . . 55, 66
Syrup heating . , . . . . 51, 66
Syrup, Inversion in . . . . 44, 64
Syrup liming . . . . . . 55
Syrup, Sodium phosphate in 48
Syrup sulphitation, Control of 39, 66
Syrup sulphitation, Order of 45
Syrup sulphitation . . . . 34, 38
Tanks, Acid syrup . . . . 45
Tanks, Agitating . . . . 50, 60
Tanks, Blow-up . . 50, 57, 58
Tanks, Clear juice . . . . 50
Tanks, Eliminating . . . . 51
Tanks, Liming. . .. .. 60
Tanks, Measuring . . . . 49
Tanks, Settling . . . . 50, 58
Tanks, Sulphitation . . . . 19, 39
Tanks, Syrup cooling . . . . 51
Tanks, Vacuum pan supply . . 51, 56
Taylor filter-presses . . . . 51
Temperature, effect on inver-
sion 44, 64
Temperature, in wax separators 58
Temperature of combustion . . 8, 65
Temperature of dissociation
of S02 6
Temperature of limed juice .. 50, 60
Temperature of sulphitated
juice 50
Temperature of syrup 39, 45, 51, 67
Theoretical purity of SO2 gas 23
Titration, Iodine . . 41, 43, 66
Two-sugar process . . . . 53
U
Uba cane, characteristics, etc.
33, 35, 58
Ultramarine .. .. 54
Vacuum pan, Free SO2 in . . 45
Vacuum pan, Oxygen in . . 45
Vacuum pan, Sulphitating in 2
Vessels, see under Tanks
Viscosity . . . . 34, 35, 46
Viscosity, Reducing . . . . 28, 46
W
Washer, Gas . . 7,9, 12, 17, 65
Wax in Natal juice . . . . 35, 58
Wax separator . . . . . . 58
White sugar, Superior 52, 54, 57
Yellow tint in crystals
z
Zerban, Dr.
THE
SUGAR MACHINERY
MANUFACTURING Co., LTD.
GROUP OF ENGINES, MILLS AND GEARINGS
IN OUR ERECTING BAY.
RECORD CRUSHING, SMOOTH RUNNING,
PERFECTION OF WORKMANSHIP.
CABLES:
PROOFSTICK, LONDON.'
ADDRESS
76 ELSHAM ROAD, LONDON, W.
THE
SUGAR MACHINERY
MANUFACTURING Co., LTD.
I THE SUGAR 'MACHINERY MANUFACTURING C9 LT°
?•.->.*.- .-. ..i.VjLO'NDON.
VIEW OF A WHITE SUGAR FACTORY
DESIGNED AND BUILT THROUGHOUT BY US.
COMPLETE FACTORIES.
EVAPORATORS, VACUUM PANS, &.C.
PROOFSTICK, LONDON.
76 ELSHAM ROAD, LONDON, W.
THE
SUGAR MACHINERY
MANUFACTURING COMPANY, Ltd.
MILL INSTALLATIONS.
CRUSHERS.
EXCELSIOR TOOTHED ROLLERS.
Two Testimonials of recent Mills made by us :
" No Mill existing in the Colony can be compared to the one sent by you
to this Estate : it is working noiselessly and doing capital crashing. "
"It is a 'glory/ both as regards perfection of manufacture and per-
formance. ' ' _———^^^__^^_^^^_
Address :
Cables:
PROOFSTICK, LONDON."
76 ELSHAM ROAD, LONDON, W.
THE
SUGAR MACHINERY
MANUFACTURING COMPANY, Ltd.
We have extensive experience in Building
entirely
New Factories
and in Reorganising Existing Factories
for the Manufacture of
WHITE SUGAR
by the
SULPHITATION
PROCESS
We are Manufacturers of all the
Machinery and Apparatus necessary for
Modern Sulphitation Work as described by
Dr. F. Maxwell in this book.
Cable Address : Head Office :
"PROOFS-TICK, 76 ELSHAM ROAD,
LONDON." LONDON, W.
THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW
AN INITIAL FINE OF 25 CENTS
WILL BE ASSESSED FOR FAILURE TO RETURN
THIS BOOK ON THE DATE DUE. THE PENALTY
WILL INCREASE TO SO CENTS ON THE FOURTH
DAY AND TO $1.OO ON THE SEVENTH DAY
OVERDUE.
APR 10 1936
M*Y 17 1939
Nml JL «
.
LD 21-100m-7,'33
i
394221
•77.
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