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albumen of which, as it coagulates, entangles many impurities, carrying
them to the surface, and so enabling them to be skimmed off, together with
some insoluble products of the action of the lime. The liquor, thus far cla-
rified, is then transferred to a series of cotton filtering bags, till it runs
through them quite bright, but still of a dark color. To decolor it, it is
passed through bone-back, or other varieties of charcoal, contained in verti-
cal metallic cylinders, the effect of which is to render the dark-colored syrup
nearly colorless and bright. In this condition, and of proper strength, it is
transferred into the vacuum pan, and boiled down under diminished pres-



GRAPE SUGAR. 569

sure, and at a temperature of about 150, till of sufficient density to be
drawn off into a vessel now termed the heater, but which when, as formerly,
the syrup was boiled down over an open fire, and at a temperature of not
less than 230, was called the cooler. Here the temperature of the syrup,
now inclined to crystallize, is raised to about 175, under constant stirring,
and it becomes a kind of magma, which is filled out into proper conical
moulds of copper, zinced iron, or earthenware, the orifice at the apex of
each mould being plugged by a paper stopper. As soon as this magma has
consolidated upon the upper surface (or the base of the cone) it is well
stirred up again, and in due time the stoppers are removed, so as to allow
the uncrystallized liquid to drain away into vessels placed for its reception.
The loaves are now submitted to a peculiar washing or cleansing operation,
sometimes called claying, which consists in the application of a thick mortar
or magma of sugar and water (now used instead of clay) to the base of the
loaf, portions of the fluid from which gradually percolate the loaf, carrying
the dark-colored syrup, or treacle, before them. Finally, an operation
termed liquoring is resorted to ; that is, a dense and very pure syrup is
poured upon the base of the loaf, previously smoothed by a bottoming trowel,
and as this filters through the cone, it deposits a portion of its sugar in its
way, and at the same time washes out the relics of colored syrup. When
this process is completed, and all percolation has ceased, the loaf is knocked
out of the mould, and if above 16 pounds' weight, is truncated by cutting
off the apex, so as to form what is called a lump, or titler ; or if intended for
a loaf proper, a new apex is given to it by a conical cutter or nosing ma-
chine. Finally, the loaves are papered, and deposited on trellised shelves in
a room called the stove, heated to about 130, till dry throughout. By
another process, which is now largely worked at Bristol, the crystallizable
syrup is placed in a perforated cylinder or sieve, which is made to revolve
with great rapidity in another vessel. The treacle or fluid portion is by
this method at once separated from the small crystals of sugar. This is
known in commerce as centrifugal sugar. It is remarkably pure.

GRAPE-SUGAR; Glucose (C M H M MI or C 12 H ia 13 +2HO). This modifi-
, cation of sugar abounds in grapes, figs, plums, and other fruits : it is also
the result of the action of diastase, and of dilute acids upon starch. In good
seasons the expressed juice of grapes yields from 30 to 40 per cent, of solid
matter, the greater part of which is this kind of sugar. When obtained
from fruits, it is accompanied by more or less of an uncrystallizable sugar
(Fruit-sugar or Fructose,^ C la H 13 12 ), which, however, by assimilating the
elements of water, passes into the condition of grape-sugar, or glucose. The
conversion of starch into this kind of sugar has been adverted to. It is a
process extensively carried on as a commercial manufacture, especially in
France. (It is used in the making of beer and in the adulteration of sugar
and honey.) Potato-starch and sago are principally used for this purpose :
they are saccharized by the action of dilute sulphuric acid (10 parts of acid
to 1000 of water and 500 of starch). The dilute acid is heated by steam,
and the starch, previously mixed with water of a temperature between 112
and 130, is suffered gradually to dribble-in under constant stirring ; its con-
version into dextrine is immediate : in about two hours and a half the whole
of the starch is added, and in from 15 to 25 minutes afterwards, the sacchari-
fication is complete ; the steam is then shut off, and the liquor transferred to
another vat, in which the acid is saturated with chalk. When the sulphate
of lime has subsided, the clear liquid is drawn off and evaporated to the sp.
gr. of about 1-26. The resulting syrup is then left to deposit the sulphate
of lime separated during evaporation, and afterwards drawn off perfectly
clear. In this state it may be used as a source of alcohol, or for sweeten-



570 ACTION OP BASES ON SUGAR.

ing colored liquors ; but it requires, for the greater number of purposes, to
be deprived of color, which is done by filtering it through animal charcoal.
When required in its solid state, the syrup is evaporated in a steam vat till
of a sp. gr. of about 1*4 and then poured into coolers, where it concretes.

Glucose, or grape-sugar, differs from sucrose, or cane-sugar, in being less
soluble in water, and more soluble in alcohol, so that the two may be to
some extent separated by the action of alcohol. The sweetening power of
glucose is also greatly inferior to that of sucrose, 2 parts of the latter being
in this respect equivalent to about 5 of the former. They both deoxidize
and discharge the color of a solution of permanganate of potash, but glucose
acts more rapidly and perfectly than sucrose. Sucrose easily crystallizes in
prisms, but glucose forms tubercular concretions, or fibrous acicular groups,
==C 13 H 12 O 13 ,2HO. Both these sugars form definite crystallizable compounds
with chloride of sodium.

When cane-sugar is heated to about 320 it melts, and at about 400 be-
comes brown, deliquescent, and slightly bitter, losing water (2 atoms), and
passing into Caramel, = C 13 H g O g . In this state it is used for coloring wines
and spirits : it is soluble in water, but is thrown down from its solution by
excess of alcohol. It combines with certain bases, such as baryta and oxide
of lead, forming insoluble compounds. Heated to about 500, melted sugar
bursts into flame, and leaves a porous mass of nearly pure charcoal.

When grape-sugar is heated to 212 it softens, and loses 2 atoms of water
becoming (C 13 H 13 O 1? ) ; at 284 it passes by further loss of water into caramel,
C 13 H 9 O g , and at a higher temperature is entirely decomposed. Solutions of
cane and of grape-sugar produce a right-handed rotation upon a ray of
polarized light.

Concentrated sulphuric acid acts energetically upon cane-sugar, evolving
water, carbonic and formic aqids, and charcoal. It is a striking experiment
to mix about equal bulks of oil of vitriol and strong syrup : the mixture,
when stirred, becomes brown and black, then suddenly heats, boils up, and
passes into the state of a bulky black magma : the acid appears suddenly to
abstract the elements of water from the sugar, leaving charcoal. The action
of sulphuric acid upon grape-sugar is very different : it merely renders it
brown, and a new compound, sulphosaccharic acid, is produced, characterized
by forming soluble salts with lime and baryta.

Boiled with very dilute sulphuric, hydrochloric, or tartaric acid, cane-
sugar becomes fruit or grape-sugar, by the assimilation of an atom of water ;
and under the influence of yeast (see ALCOHOLIC FERMENTATION) there is a
similar transition of the one species of sugar into the other ; but the con-
verse change, namely, that of grape or fruit-sugar into cane-sugar (glucose
into sucrose), cannot be effected. Nitric acid changes the varieties of sugar
into saccharic and oxalic acids. In the presence of decomposing casein arid
chalk, sugar forms lactic acid, and under the influence of certain substances
occasionally present in raw sugar, it passes into a ropy mucilage and into
mannite.

Action of bases upon Sugar. When lime or baryta is boiled with sugar-
and water a bitter solution is formed, which is said to contain a definite
saccharide (2CaO, or 2BaO, + C ta H 9 9 ). Freshly precipitated oxide of lead
is similarly dissolved, and on cooling, a white compound falls, which, after
having been dried at 212, is = 2PbO-f C 13 H 9 9 . Alcohol does not pre-
cipitate sugar from its solution in water, and tannic acid and iodine water
have no effect upon it. The aqueous solution gives no precipitate with a
salt of lead, but on adding ammonia the sugar combines with and is precipi-
tated with oxide of lead. Many of these compounds are soluble in excess
of alkalies, and hence the presence of sugar sometimes prevents the precipi-



TESTS FOR SUGAR. 571

tation of metallic oxides from their salts. In other cases sugar tends to
reduce the oxides. The compounds of glucose with bases are less stable than
the preceding, this sugar gradually passing into glucic acid (C 12 H 5 5 ,3HO),
which under the influence of heat becomes apoglucic acid (C 18 H B S ,2HO) :
and ultimately melassic acid is formed. Grape-sugar is distinguished from
cane-sugar by boiling it in a solution of potassa. The former alone darkens
as the result of the formation of glucic acid. This is commonly known as
Moore's test.

Tests for Sugar. The deoxidizing property of glucose above mentioned
is the foundation of a valuable test of its presence ; and inasmuch as the
other varieties of sugar are transformed into glucose by the joint action of
very dilute acids and heat, the same mode of testing is applicable to sugar
generally. Certain salts of copper and of platinum are especially applicable
to these purposes. When a little cane-sugar is added to a dilute solution of
copper, and the mixture heated, little immediate change ensues ; but with
grape-sugar the blue color of the liquor is presently changed to green, it
then becomes yellowish or reddish-brown, and suboxide of copper or metallic
copper falls: these changes are more rapid when a little alkali has been
added to the solution. Thus if a few drops of a very diluted solution of
sulphate of copper are added to a solution of either sugar a slight color is
imparted. A small quantity of a solution of potash causes in the mixture
a precipitate of blue hydrated oxide of copper. An excess of the alkaline
liquid dissolves this precipitate, forming a sapphire-blue solution. When
this is heated the grape-sugar causes rapidly the changes above mentioned
the yellow precipitate formed being the hydrated suboxide and the red pre-
cipitate the anhydrous suboxide. Pure cane-sugar thus treated does not
easily decompose the salt of copper. It requires long boiling to produce
any decomposition. With grape-sugar it usually takes place upon slightly
warming the liquid and before it has reached the boiling point. One form
of the copper test as it is sometimes employed for the detection of sugar is
the soda tartrate of copper^ obtained by dissolving recently precipitated
tartrate of copper in a solution of soda or of carbonate of soda : it is imme-
diately reduced when boiled with a trace of glucose ; used quantitatively, it
will be found that 15 parts of the precipitated or red suboxide of copper are
equivalent to about 5 of cane-sugar, and to about 5't of grape-sugar. The
copper test for sugar has been long known under the name of Trommels test.
Some precautions are required in its employment. If sugar is not present
potash has no solvent action on the precipitated oxide of copper, and on
boiling the colored liquid, black or anhydrous oxide of copper only is
thrown down. On the other hand, a solution of the precipitated oxide by
an excess of alkali does not indicate the presence of sugar. In the presence
of albumen, casein, glycerine, mannite, or any alkaline tartrate, potash re-
dissolves the precipitated oxide, forming a blue or purple-blue liquid : but
on boiling the liquid, there is no reduction of the oxide of copper, and no
red suboxide is produced. If chloroform is present, even in small quantity,
the oxide of copper is not redissolved by an excess of potash, but it under-
goes a complete reduction to suboxide on boiling it. Here the non-redissolu-
tion would distinguish chloroform from sugar. On the other hand, arsenious
acid or an alkaline arsenite, when present, forms a clear blue liquid with a
salt of copper and an excess of potash ; and on boiling the solution, the red
suboxide of copper is precipitated as if sugar were really present. The test
when properly employed is with proper precautions adequate to the detection
of sugar under all circumstances. Although the presence of pure cane-sugar
is not readily indicated by the test, yet on warming the solution for a short



572 HONEY. MANNITE.

time, with a few drops of tartaric or very dilute sulphuric acid, the cane is
converted into grape-sugar, and it will then immediately respond to the test.

A hot solution of nitrate of suboxide of mercury is immediately blackened
by glucose, and finely-divided mercury falls : -in the same way a boiling
solution of corrosive sublimate deposits calomel, which is afterwards partially
reduced : red oxide of mercury is also reduced when boiled in the saccharine
solution. Solutions of nitrate of silver and of chloride of gold, when boiled
with glucose, afford precipitates of silver and gold : when in these cases,
excess of .carbonate of soda is present, the effect is more rapid, and in this
way the chlorides of platinum and palladium are reduced. A delicate test of
glucose is the soda-chloride of platinum formed by adding excess of a solution
of carbonate of soda to a moderately dilute solution of chloride of platinum.
When this solution is boiling, a small portion of cane-sugar dropped into it
produces no effect, but it is instantly discolored, and ultimately blackened,
by the smallest trace of grape-sugar. Where these tests are used, the absence
of other organic matters likely to effect their decomposition, must be insured.

The ultimate components of the preceding varieties of sugar are as fol-
lows :

SUCROSE. GLUCOSE.

Atoms. Equiv. Per cent. Atoms. Equiv. Per cent.

C 12 ... 72 ... 42-11 C 12 ... 72 ... 36-36

H 11 ... 11 ... 6-43 H 14 ... 14 ... 7-08

11 ... 88 ... 51-46 14 ... 112 ... 56-56



1- 171 100-00 1- 198 100-00

Fructose or Levulose exists chiefly in fruits, but it does not appear to be
an independent sugar, although the formula C 12 H 12 12 is usually assigned to
it. It is not crystallizable : it is quite soluble in alcohol, and turns the plane
of the polarization to the left : hence it is sometimes called inverted sugar.
After a time it seems to be spontaneously converted into crystallized grape-
sugar or glucose. Thus white fresh grapes contain fructose, the dried raisins
contain glucose.

Honey. The substance secreted in the nectaries of flowers is converted
by the bee into honey and wax : the portion not required for their food is
returned into the combs in the form of a yellow syrup, the qualities of which
differ according to the flowers whence it has been derived. In its original
liquid state it probably resembles uncrystallizable sugar of fruits, &c. (Fruc-
tose, C 12 H 13 O 12 ) ; but when kept for some time, a large portion of it passes
into a granular form, identical with glucose = C 12 H O M . But honey also
contains a little wax, gum, coloring matter, and mannite.

Diabetic Sugar, or that which is formed in a diseased state of the animal
system (diabetes), has all the properties of grape-sugar or glucose. It may
be separated from the extract of diabetic urine by boiling alcohol.

Mannite ; Manna-Sugar (C 6 H 7 6 ). This substance is most abundant in
manna, but it is also found in the beetroot, celery, asparagus, onions, and
probably in other sweet plants : it is also contained in the sap of the larch, and
other species of pinus (Manna Brigantina). It has been detected by Dr.
Stenhouse in Laminaria Saccharina, and some other fuci. Manna exudes
from several species of ash, especially from the Fraxinus ornus and rotundi-
folia. Mannite is obtained by boiling manna in alcohol, from which it
crystallizes on cooling in acicular prisms. It forms about four-fifths of the
best manna; the residue being chiefly common sugar, and a peculiar ex-
tractive matter, in which the aperient quality of the manna is said to reside.
Mannite is also an occasional product of the viscous fermentation.

Mannite is very soluble in water, but is not susceptible of vinous fermen-



FERMENTATION. 513

tation, so that it may in this way be separated from the other varieties of
sugar ; for, when mixed with them, it remains undecomposed in that process.
Nitric acid converts it into saccharic and oxalic acids, without any trace of
mucic acid. Its aqueous solution precipitates basic acetate of lead, forming
a compound in which 2 equivalents of water are replaced by two of oxide of
lead, = C H 5 4 ,2PbO. It reduces chloride of gold and nitrate of silver.
With precipitated oxide of copper it forms a clear blue liquid on the addition
of an excess of alkali, but there is no decomposition or reduction on boiling.
"When a solution of mannite is boiled with an excess of a solution of potash
no glucic acid is produced, and the liquid does not darken. When heated
with diluted acids, mineral or vegetable, it is not converted into glucose. It
combines with sulphuric acid, forming sulphomannitic acid, =C 8 H 5 4 , 2S0 3 .

Glycyrrhizine (C 35 H 32 12 ) is the sweet principle of liquorice-root: it forms
with many acids and bases compounds which are not very soluble, and it is
not susceptible of vinous fermentation.

There are some other substances allied to these modifications of sugar,
which do not require detailed notice, such as Melitose and Eucalyn, the pro-
duce of the Eucalyptus munnifera ; Sorbine, from the berries of the mountain-
ash ; Quercite, from acorns.



CHAPTER XLVI.

ALCOHOLIC OR VINOUS FERMENTATION. ALCOHOLIC

LIQUIDS.

BY fermentation, we are to understand the conversion of an organic
substance into one or more new compounds, in presence of a body called
a ferment. , Hence there are various kinds of fermentation, designated
according to their products vinous or alcoholic, lactic, butyric, acetous, &c.
In vinous fermentation sugar is resolved into alcohol and carbonic acid.
Sugar itself is not absolutely necessary to the process ; for starch, dextrine,
or any substance capable of being easily converted into sugar, under the
circumstances, may be substituted, and similar products obtained. The
conversion of the substance into sugar appears to be, however, an essential
preliminary condition for the establishment of the process. It is well known
that a portion of malt or saccharized barley, mixed with unmalted grain, will
produce alcohol the starch and dextrine of the unmalted grain being con-
verted into sugar during the process. In the same way alcohol may be pro-
duced in large quantity, by the mixture of the starchy pulp of the potato with
a portion of treacle. The fermentation of dough in the making of bread
appears to depend on similar principles ; a'portion of the starch is converted
into sugar, and, in the presence of a ferment, the sugar is immediately
resolved into alcohol and carbonic acid.

Pure sugar, extracted from the vegetable and dissolved in water, has no
tendency to undergo this remarkable change. A solution of pure cane-
sugar is slowly converted into grape-sugar, but there the change stops : no
alcohol is produced. The saccharine juices of vegetables, however, readily
ferment, owing to the presence of a nitrogenous principle with which they
are usually associated. This is called a ferment. It is an organic compound



574 FERMENTATION. PRODUCTION OF FERMENTS.

containing nitrogen, and is readily susceptible of change by simple exposure to
air. In this state it possesses the property of rapidly inducing changes in any
saccharine liquid. Gay-Lussac observed long since, that when fresh grape-
juice was collected in a vessel containing carbonic acid, and placed over
mercury, no fermentation took place, although all other circumstances* were
favorable to this process. When the juice was exposed to air and a proper
temperature, it rapidly fermented, and when once this fermentation had com-
menced, it continued until the saccharine matter was entirely decomposed.
If to the unfermented juice, placed over mercury, a few bubbles of air or
oxygen were admitted, the same change took place, and continued until the
sugar was exhausted, a large quantity of carbonic acid being at the same
time evolved, while the liquid was found to have lost its saccharine, and to
have acquired a spirituous or alcoholic flavor. These facts prove that there
is present in grape-juice a substance which, by contact with oxygen, under-
goes a change, and becomes a ferment ; and further, that the saccharine
juices of fruits do not ferment, because the access of free oxygen is cut off by
the epidermis of the fruit.

A saccharine solution of malt, called wort, will undergo similar changes,
by reason of the nitrogenous principles contained in the grain. The custom
is, however, to add to the liquid, for the purpose of accelerating the change,
a quantity of a nitrogenous compound called yeast, or barm, derived from a
previous fermentation. This constitutes the ferment. It produces a rapid
conversion of the saccharine matter into alcohol and carbonic acid ; and at
the same time causes the separation of the nitrogenous principles of the wort
in the form of additional ferment or yeast. The quantity of new yeast thus
procured, amounts to seven or eight times the quantity of that which has
been added to the wort.

It has been shown by Mitscherlich (Poggend. Ann., iv. 224), that the
actual contact of the particles of the yeast with the dissolved sugar is
essential. He suspended a wide glass tube, the bottom of which was closed
with bibulous paper, in a jar of a solution of sugar, the tube being itself filled
with the same solution. Some yeast was then put into the syrup contained
in the tube, where it soon induced fermentation, and the alcohol there formed,
passed through the pervious bottom, and, together with carbonic acid,
diffused itself in the surrounding liquor : but the actual phenomena of fer-
mentation namely, the decomposition of the sugar and the formation of
alcohol and of carbonic acid were limited to the syrup in the tube contain-
ing the ferment, and the sugar in the outer vessel remained unchanged.
Quevenne found that yeast which had been deprived of all matter soluble in
water, still retained its power of exciting fermentation. The active part of
yeast is composed of minute vesicles, or globules, and during fermentation
these germinate in the saccharine liquor, producing a microscopic fungus, the
Torula or Mycoderma cerevisise. The plant, according to one theory of the
process, is supposed to grow at the expense of the sugar, giving out carbonic
acid, and leaving alcohol. According to Andral and Gavarret (Ann. Gh. et
Ph., Seme ser., viii. 399), there are two species of vegetable seeds contained
in yeast, which may be separated by diluting it with water : in a few days
globules fall to the bottom of the vessel, forming a gray pulverulent deposit
which is extremely active in producing alcoholic fermentation when added to
saccharine solutions ; but at the same time a film forms upon the surface of
the liquid, which consists of germs (of Penicullum glaucum) having no
power to excite fermentation : these latter germs make their appearance in
all acid albuminous liquids, and become filamentous, while the true producer
of alcoholic fermentation always retains its globular form. According to



CONDITIONS WHICH INFLUENCE FERMENTATIONS. 575

Mitscherlich, the active part of yeast which remains after it has been washed
with water, consists of:

Before fermentation. After fermentation.

Carbon 47'0 47-6



Hydrogen . . .6-6

Nitrogen . . . .10-0

Oxygen 35-8

Sulphur . . ... 0*6



7-2
5.



Of this yeast (in the dry state) from 2 to 3 parts are required for the
decomposition of 100 parts of sugar : and if there is excess of sugar, it
remains unchanged after the fermentation. That portion of the yeast which
remains in the form of a deposit after fermentation is over, is inefficient as a
ferment ; it appears, when examined under the microscope, to consist of the
ruptured cells, and is not susceptible of vegetation ; so that during the
fermentation of sugar, a certain portion of the yeast-plant dies, and is decom-



Online LibraryWilliam Thomas BrandeChemistry → online text (page 87 of 124)