Raw, or muscovado sugar, as imported from the colonies, is contaminated
more or less with gluten, lime, but particularly _caramel_, which give
its grains a yellow brown tint, an empyreumatic odour, and a soft clammy
feel in the hand. If such sugar be dissolved in water, and the syrup be
evaporated by a gentle heat, it will afford a sugar of still inferior
quality and appearance. This rapid deterioration is in some measure
owing to the injurious operation of a prolonged heat upon the
crystalline structure, but chiefly to the chemical reaction of the
glutinous ferment and lime upon the sugar. The first care of the refiner
should therefore be the immediate abstraction of these noxious
alteratives, which he effects by the process called _meltings_; that is,
mixing up the sugar in a pan with hot water or steam into a pap, and
transferring this pap into large sugar-moulds. Whenever these become
cool, their points are unplugged, and they are set to drain for a few
days in a warm apartment. Sugar thus cleansed is well prepared for the
next refining process; which consists in putting it into a large square
copper cistern along with some lime-water, (a little bullock’s blood,)
and from 5 to 20 per cent. of bone black, and blowing it up with steam;
or, in other words, injecting steam through the mixture from numerous
orifices in copper pipes laid along the bottom and sides of the vessel.
Under the influence of the heat and agitation thus occasioned, the
saccharine matter is perfectly dissolved and incorporated with the
albumen of the blood and the bone black. Instead of the blood, many
refiners employ a mixture of gelatinous alumina and gypsum, called
_finings_, prepared by adding a solution of alum to a body of
lime-water, collecting, washing, and draining the precipitate upon a
filter. Other refiners use both the blood and finings, with advantage.
Bone black is now very frequently employed by the sugar-refiner, not in
a fine meal, but in a granular state, like corned gunpowder, for the
purpose of decolouring his syrups; in which case, he places it in a box,
in a stratum 8 or 10 inches thick, and makes the syrup percolate
downwards through it, into a cistern placed beneath. By this means it is
deprived of colour, and forms the _claircé_ of the French refiner. When
the blowing up cistern is charged with sugar, finely ground bone black,
and blood, the mixture must be passed through a proper system of
filters. That now most in use is the creased bag filter, represented in
_figs._ 1084, 1085, 1086.
[Illustration: 1084 1085 1086]
The apparatus consists of an upright square wooden case _a_, _a_, about
6 or 8 feet high, furnished with a door of admission to arrange the
interior objects; beneath is a cistern with an educting-pipe for
receiving and carrying off the filtered liquor; and above the case is
another cistern _e_, which, like the rest, is lined with tinned sheet
copper. Into the upper cistern, the syrup mixed with animal charcoal is
introduced, and passes thence into the mouths _e_, _e_, of the several
filters _d_, _d_. These consist, each of a bag of thick tweeled cotton
cloth, about 12 or 15 inches in diameter, and 6 or 8 feet long, which is
inserted into a narrow bottomless bag of canvas, about 5 inches in
diameter, for the purpose of folding the filter-bag up into a small
space, and thus enabling a great extent of filtering surfaces to be
compressed into one box. The orifice of each compound bag is tied round
a conical brass month-piece or nozzle _e_, which screws tight into a
corresponding opening in the copper bottom of the upper cistern. From 40
to 60 bags are mounted in each filter case. The liquor which first
passes is generally tinged a little with the bone black, and must be
pumped back into the upper cistern, for refiltration. In cold weather
the interior of the case may be kept warm by a proper distribution of
steam-pipes. _Fig._ 1085. shows one mode of forming the funnel-shaped
nozzles of the bags, in which they are fixed by a bayonet catch. _Fig._
1086. shows the same made fast by means of a screwed cap, which is more
secure.
The next process in sugar-refining is the evaporation of the clarified
syrup to the granulating or crystallizing pitch. The more rapidly this
is effected, and with the less scorching injury from fire, the better
and greater is the product in sugar-loaves. No apparatus answers the
refiner’s double purpose of safety and expedition so well as the
vacuum-pan of Howard.
[Illustration: 1087]
_Fig._ 1087. shows the structure of a single vacuum-pan. The horizontal
diameter of the copper spheroid A, is not less than 5 feet; the depth of
the under hemisphere is at least 18 inches from the level of the plane;
and the height of the dome-cover is 2 feet. The two hemispheres (of
which the inferior one is double, or has a steam-jacket,) are put
together by bolts and screws, with packing between the flanges to
preserve the joints tight against atmospheric pressure. The jacket of
the lower hemisphere forms the case of the steam, which communicates
heat to the syrup enclosed in the inner hemisphere. In general, the pans
contain, when filled to the flange, 100 gallons of syrup, and yield
about 11 cwt. of granulated sugar, at every charge.
A, represents the vacuum spheroid; B, the neck with the lid. From the
side of B, a pipe passes into the lower extremity of the bent pipe C, D,
which terminates in the vertical pipe E, connected with the vacuum
main-pipe K, proceeding horizontally from the air-pump (not shown in the
figure). At the top of E, a valve, movable by a screw H, is placed for
establishing or cutting off the connexion with the air-pump at pleasure.
Behind F, is the measure cistern, from which the successive charges are
admitted into the pan. This measure is filled with the clear syrup, by
opening the stopcock I, on the pipe under the ceiling, which
communicates with the filter-cistern placed above. G is the valve or
plug-hole, at the bottom of the pan, for discharging the granulating
syrup. This plug is opened by means of a powerful lever attached to it;
the connexion with the air-pump being previously intercepted. L, is the
barometer, or manometer, for showing the state of the vacuum
corresponding to the temperature. N, N, is a cistern-pipe for receiving
any little syrup which may accidentally boil over the neck B. Its
contents are let off by a stopcock at its bottom from time to time. M
shows the place of the _proof-stick_, an ingenious brass rod for taking
out a sample of syrup without admitting air. See _infrà_.
The charging-cistern contains about 20 gallons. This quantity of syrup
being first admitted, and brought to a certain pitch of concentration, a
second measure is introduced, the inspissation of which is supposed by
some refiners to cause an agglomeration of saccharine matter round the
first crystalline particles. The repetition of this process for two or
three times is imagined to produce the large brilliant grain of
vacuum-pan sugar. This hypothesis is more specious than sound, because
the granulating syrup discharged from the pan is subjected to a heat of
180° or 190° in the subjacent steam-cased receiver, whereby the
granulations are again reduced to a very small size. Into this receiver,
two or three skippings or discharges of the pan are admitted in
succession, and the whole are diligently mixed and agitated by a
stirring oar. It is by this process that the granulating tendency is
promoted and determined. From this receiver (absurdly enough called a
cooler) the moulds are filled in the usual way, by means of copper
basins or large ladles.
The case of the under hemisphere of the vacuum-pan is filled with steam,
generated under a pressure of four or five pounds on the square inch;
the heat of which causes the interior syrup to boil rapidly while the
air-pump is kept in action. A small escape-pipe for waste steam must be
placed at the opposite side of the case or jacket, to ensure its equal
distribution; as also a stopcock below, to let off the water of
condensation. The pans are mounted on iron feet, or short pillars, which
insulate them from the floor, and allow their whole surface to be
inspected, and any flaw to be repaired. The air-pump usually stands in a
cold-water cistern, to favour the condensation of the aqueous vapour,
which it draws out of the pans; and it is kept in constant action by the
steam-engine, being attached to the working-beam of its piston.
[Illustration: 1088]
_Fig._ 1088. exhibits the general arrangement of the vacuum-pans, and
their subsidiary apparatus. Here are shown, on the ground floor, the
heaters _e_, _e_, (miscalled coolers), into which the concentrated syrup
is let down. These heaters are made of copper, in one piece, surrounded
with a cast-iron jacket, bolted at the flange or brim to it. Each pan
contains, when full, about 350 gallons, equivalent to nearly 35 cwt. of
crystallized sugar. They are furnished with steam-cocks and waste
steam-pipes. Under the level of the spheroids _d_, _d_, the horizontal
main-pipe is seen, for supplying the cases with steam. In the face of
each pan, above the line _b_, _b_, the handle of the proof-stick
appears, like that of a stop-cock. The distribution of the measure
cisterns, and some other parts of the pans, is slightly varied in this
representation from the former. From the bottom of the liquor cisterns
C, C, pipes descend to the charging measures _a_, _a_, below. The
cisterns C, C, are made of copper, and contain each about 400 gallons.
Six tons of refined sugar can be turned out daily in a three-pan house.
[Illustration: 1089]
_Fig._ 1089. represents in section another form of the vacuum-pan, _a_
is the spheroidal copper vessel, supported by four iron columns _b_,
_b_. It may be discharged by means of the pipe _c_, which is secured
with a conical valve _d_. This may be opened or shut, by acting on the
lever _e_. The lower of the two hemispheres of which the pan is
composed is double, and the interstitial space _f_, _f_, is filled with
steam by the pipe _g_, as the heating and evaporating agent. _h_, is the
steam valve; _i_, the pipe for the efflux of the condensed water. _k_, a
tube for the escape of the air at the commencement of the operation.
_l_, is an apparatus inserted air-tight into the cover of the
vacuum-pan, and which dips down into the syrup; serving to take out a
sample of it, without allowing air to enter, and hence called the
proof-stick. The construction of this instrument is exhibited in _figs._
1091, 1092, 1093, 1094, 1095., which will be presently explained. _m_,
is the thermometer, which is also plunged into the sugar; behind it, is
the barometer. _n_, is the charger or gauge-vessel, filled with the
filtered syrup, which it discharges by the pipe _n´_. _o_, is the cover
or capital of the vacuum-pan. _o´_, is a safety-valve, through which the
air may be admitted, after the completion of the process. _p_, is a bent
pipe, slanting downwards, with a stopcock _q_, at its end, to receive
the superfluous syrup. The vapour, which is disengaged from the syrup
during its concentration, is extracted from the top of the pan into the
pipe _r_, passes from this into the vessel _s_, which is divided by a
plate of copper into two compartments. The syrup forced over
accidentally in the ebullition, goes into the vessel _s_, and passes by
the glass tube _t_, into the pipe _p_. The glass tube serves to show the
quantity of the syrup that has boiled over, so that it may be drawn off
when necessary. For this purpose, the stopcock _u_, of the vessel _v_,
must be closed, and _q_ must be opened, in order to fill _v_, while the
air contained in it escapes into the pan. The stopcock _q_, being then
shut, and _u_, with the little air-cock _x_, opened, the syrup will flow
into the large receiver placed beneath it, commonly but erroneously
called a cooler; because it is a double copper basin, with steam in the
interstitial space. The hot steam rushes from _s_, into the cast-iron
vessel _y_, where it is condensed. _z_, is a pipe for introducing the
water of condensation through the copper rose _a´_. The condensed water
flows through the pipe _b´_, and the valve _e´_, to the air-pump, which
receives motion from the shaft of the steam-engine.
[Illustration: 1090]
The vacuum-pan was originally heated solely by the admission of steam
between the double bottom; but of late years the heat has been also
applied to the syrup through several coils of pipe placed within the
pan, filled with steam at a temperature many degrees above 212° F.,
sometimes so high as 250°. By this double application of heat, the
evaporating power of a pan has been vastly increased. The latest made
pans have a considerably flat bottom, _fig._ 1090.; a spiral pipe, laid
close upon it; and between the under hemisphere and the upper one, there
is a space _a_, _a_, 2-1/2 feet high, to give the syrup room for
frothing up without boiling over. The space _b_, of the bottom receives
steam of common pressure, and the spiral tubes, of high pressure. A pan
like this is now making for a house in London, which is to work off 16
tons of sugar-loaves daily.
[Illustration: 1091 1092 1093 1094 1095]
The proof-stick, _fig._ 1095., consists of a cylindrical rod, capable of
being screwed air-tight into the pan in an oblique direction downwards.
The upper or exterior end is open; the under, which dips into the syrup,
is closed, and has on one side a slit _a_ (_figs._ 1091, 1092.), or
notch, about 1/2 inch wide. In this external tube, there is another
shorter tube _b_, capable of moving round in it, through an arc of 180°.
An opening upon the under end _e_, corresponds with the slit in the
outer tube, so that both may be made to coincide, _fig._ 1091. A. A
wooden plug _d_, is put in the interior tube, but so as not to shut it
entirely. Upon the upper end there is a projection or pin, which catches
in a slit of the inner tube, by which this may be turned round at
pleasure. In the lower end of the plug there is a hole _e_, which can be
placed in communication with the lateral openings in both tubes. Hence
it is possible, when the plug and the inner tube are brought into the
proper position, A, _fig._ 1091., to fill the cavity of the wooden rod
with the syrup, and to take it out without allowing any air to enter.
In order to facilitate the turning of the inner tube within the outer,
there is a groove in the under part, into which a little grease may be
introduced.
Whenever a proof has been taken, the wooden plug must be placed in
reference to the inner tube, as shown in _fig._ 1091. _c_, and then be
turned into the position A; when the cavity of the plug will again be
filled with syrup. _c_ must be now turned back to the former position,
whereby all intercourse with the vacuum-pan is cut off; the plug being
drawn out a little, and placed out of communication with the inner tube.
The plug is then turned into the position B, drawn out, and the proof
examined by the fingers.
TABLE showing the boiling point of syrup, at the corresponding
atmospheric pressure within the vacuum-pan:--
Height of the mercury (inches) in one leg of the syphon, above
that in the other--
0·74 0·86 1·01 1·17 1·36 1·57 1·80 2·05 2·36 2·72 3·10 3·52 4·00.
Boiling point, Fahr.--
115° 120° 125° 130° 135° 140° 145° 150° 155° 160° 165° 170° 175°.
The large double steam-basin, which receives several successive
skippings of the concentrated granulating syrup, serves to heat it from
the temperature of 160° or 170°, at which it leaves the vacuum-pan, up
to 200° or thereby, before it is filled out into the moulds; for were it
introduced in the cooler state, it would not concrete into sufficiently
compact loaves.
[Illustration: 1096 1097]
The following apparatus is used in many French sugar-houses, for
concentrating syrups, called the _swing pan_, or _chaudière à bascule_.
It is represented in _fig._ 1096. in elevation, and in _fig._ 1097. in
ground plan. _a_, is the pan; _b_, its spout; _c_, the axis or pivot
round which it swings, so as to empty itself, when raised behind by the
chain _d_; _e_, is the furnace door; _f_, the passage to the fireplace
and grate _g_; _h_, _h_, _h_, side flues for conducting the smoke into
the chimney.
The duly clarified, concentrated, granulated, and reheated syrup, is
transferred, by means of copper basins, from the coolers into conical
moulds, made either of brown and somewhat porous earthenware, or of
sheet iron, strongly painted. The sizes of the moulds vary, from a
capacity of 10 pound _loaves_, to that of 56 pound _bastards_--a kind of
soft brown sugar obtained by the concentration of the inferior syrups.
These moulds have the orifices at their tips closed with bits of twisted
paper, and are set up in rows close to each other, in an airy apartment
adjoining the coolers. Here they are left several hours, commonly the
whole night, after being filled, till their contents become solid, and
they are lifted next morning into an upper floor, kept at a temperature
of about 80° by means of steam pipes, and placed each over a pot to
receive the syrup drainings--the paper plug being first removed, and a
steel wire, called a piercer, being thrust up to clear away any
concretion from the tip. Instead of setting the lower portion of the
inverted cones in pots, some refiners arrange them in wooden racks, with
their apices suspended over longitudinal gutters of lead or zinc, laid
with a slight slope upon the floor, and terminating in a sunk cistern.
The syrup which flows off spontaneously is called green syrup. It is
kept separate. In the course of two or three days, when the drainage is
nearly complete, some finely clarified syrup, made from loaf sugar,
called _liquor_ by the refiners, is poured to the depth of about an inch
upon the base of each cone, the surface having been previously rendered
level and solid by an iron tool, called a bottoming trowel. The liquor,
in percolating downwards, being already a saturated syrup, can dissolve
none of the crystalline sugar, but only the coloured molassy matter;
whereby, at each successive liquoring, the loaf becomes whiter, from the
base to the apex. A few moulds, taken promiscuously, are emptied from
time to time, to inspect the progress of the blanching operation; and
when the loaves appear to have acquired as much _colour_, according to
the language of refiners, as is wanted for the particular market, they
are removed from the moulds, turned on a lathe at the tips, if
necessary, set for a short time upon their bases, to diffuse their
moisture equally through them, and then transferred into a stove heated
to 130° or 140° by steam pipes, where they are allowed to remain for two
or three days, till they be baked thoroughly dry. They are then taken
out of the stove, and put up in blue paper for sale.
In the above description of sugar-refining, I have said nothing of the
process of claying the loaves, because it is now nearly obsolete, and
abandoned in all well-appointed sugar-houses. Those of my readers who
desire to become acquainted with sugar-refining upon the old plan, may
consult my Report made upon the subject to the Honourable HOUSE of
COMMONS in July 1833; where they will find every step detailed, and the
numerical results stated with minute accuracy. The experiments
subservient to that official report were instituted purposely to
determine the average yield or product, in double and single refined
loaves, lumps, bastards and treacle, which different kinds of sugar
would afford per cwt., when refined by decolouring with not more than 5
per cent. of bone black, boiling in an open pan, and clearing the loaves
with clay-pap.