Cubic centimeters Cubic centimeters
of juice for 26.048 of juice for 16.19
Degrees factor. Divide Degrees factor. Divide
brix. reading by two. brix. reading by three.
5.0 51.1 5.0 47.6
5.4 51.0 5.7 47.5
5.7 50.9 6.3 47.4
6.4 50.8 6.8 47.3
6.9 50.7 7.3 47.2
7.4 50.6 7.8 47.1
7.9 50.5 8.3 47.0
8.4 50.4 8.9 46.9
8.9 50.3 9.5 46.8
9.4 50.2 10.0 46.7
9.9 50.1 10.5 46.6
10.4 50.0 11.0 46.5
10.9 49.9 11.6 46.4
11.4 49.8 12.1 46.3
11.9 49.7 12.7 46.2
12.4 49.6 13.3 46.1
12.9 49.5 13.8 46.0
13.4 49.4 14.3 45.9
13.9 49.3 14.8 45.8
14.4 49.2 15.3 45.7
14.9 49.1 15.9 45.6
15.4 49.0 16.4 45.5
15.9 48.9 17.0 45.4
16.4 48.8 17.5 45.3
16.9 48.7 18.0 45.2
17.4 48.6 18.6 45.1
17.9 48.5 19.1 45.0
18.4 48.4 19.7 44.9
18.9 48.3 20.2 44.8
19.4 48.2
19.9 48.1
In ordering sucrose pipettes the factor for which they are to be
graduated should be stated.
It is evident also that with the help of the foregoing table the
measurements may be made by means of a burette. For instance, if the
degree brix is found to be 19.9, 48.1 cubic centimeters are to be used.
This quantity can be easily run from a burette. In order to make the
pipette more convenient it has been customary in this laboratory, as
practiced by Carr, to attach a glass tube with a stopcock by means of
a rubber tube to the upper part of the pipette, whereby the exact
level of the juice in the stem of the pipette can be easily set at any
required mark.
In the polarization of dilute solutions, such as are found in the
saps and juices referred to above, it must not be forgotten that the
gyrodynat of the sucrose is increased as the density of the solution
is diminished. This change introduces a slight error into the work
which is of no consequence from a technical point of view, but
becomes a matter which must be considered in exact determinations. To
avoid the annoyance of calculating the gyrodynat for every degree of
concentration, tables have been constructed by Schmitz and Crampton by
means of which the actual percentage of sugar, corresponding to any
degree of polarization, is determined by inspection. These tables may
be used when extremely accurate work is required.[173]
[Illustration: FIGURE 64. GIRD’S GRAVIMETER.]
=207. Measuring Sugar Juices with a Gravimeter.=—A convenient method of
weighing sugar juices is the gravimetric process designed by Gird.[174]
The apparatus is fully illustrated by Fig. 64. The hydrometer F has a
weight of 26.048 grams and its stem is also graduated in degrees brix.
The juice is poured into the cylinder A and allowed to stand until air
bubbles have escaped. In filling A the finger is held over the orifice
G so that the siphon tube B is completely filled, the air escaping at
the vent C. After the tube is filled the finger is withdrawn from G and
all the liquid which will run out at G allowed to escape. The sugar
flask D is now brought under G and the hydrometer F allowed to descend
into A. The hydrometer will displace exactly its own weight of liquid.
For convenience of reading, the index E may be used which is set five
degrees above the surface of the liquid in A. The number of degrees
brix read by E is then diminished by five. The hydrometer has been
improved since the description given by the addition of a thermometer
which, in addition to carrying a graduation in degrees, also shows the
correction to be made upon the degree brix for each degree read. It is
evident that the hydrometer may be made of any weight, and thus the
delivery of any desired amount of juice be secured.
=208. Determination of Reducing Bodies in Cane Juices.=—Sucrose in
cane juices is constantly accompanied with reducing sugars, or other
bodies which have a similar action on fehling liquor, which interfere
to a considerable degree with the practical manufacture of sugar. It is
important to determine with a moderate degree of accuracy the quantity
of these bodies. These sugars or reducing bodies are of a peculiar
nature. The author pointed out many years ago that these reducing
bodies were without action on polarized light, and for this reason
proposed the name anoptose as one characteristic of their nature.[175] It
is also found that these bodies do not yield theoretically the quantity
of alcohol which a true sugar of the hexose type would give.[176] It is
entirely probable, therefore, that they are quite different in their
nature from many of the commonly known sugars. On account of the
difficulty of separating these bodies in a pure state their actual
copper reducing power is not known. For practical purposes, however, it
is assumed to be the same as that of dextrose or invert sugar and the
percentage of these bodies present is calculated on that assumption.
In the determination of these sugars or reducing bodies, the quantity
weighed may be determined by an apparatus entirely similar to the
sucrose pipette just described above. The quantity of juice used should
be diluted as a rule to such a degree as not to contain more than one
per cent of the reducing bodies. For the best work, the juices should
be clarified with lead subacetate and the excess of lead removed with
sodium carbonate. For technical control work in sugar factories, this
process may be omitted as in such cases rapidity of work is a matter
of considerable importance and the approximate estimation of the total
quantity of reducing bodies is all that is desired.
For volumetric work, the solution of copper and the method of
manipulation described in paragraph =117= are most conveniently used.
=209. Preservation of Sugar Juices for Analysis.=—Lead subacetate not
only clarifies the juices of canes and thus permits of their more exact
analytical examination, but also exercises preservative effects which
enable it to be used as a preserving agent and thus greatly diminish
the amount of work necessary in the technical control of a sugar
factory. Instead, therefore, of the analyst being compelled to make an
examination of every sample of the juice, aliquot portions representing
the different quantities can be preserved and one analysis made for
all. This method has been thoroughly investigated by Edson, who also
finds that the errors, which may be introduced by the use of the lead
subacetate in the analytical work, may be entirely avoided by using the
normal lead acetate.[177]
In the use of the normal lead acetate, much less acetic acid is
required in the polariscopic work than when the subacetate is used.
The normal lead acetate is not so good a clarifying agent as the
subacetate, but its efficiency in this respect is increased by the
addition of a little acetic acid. In its use, it is not necessary to
remove the lead, even for the determination of the reducing bodies.
For further details in regard to the technical determination of
reducing bodies, special works may be consulted.[178]
=210. Direct Determination of Sugars in Canes.=—The methods, which
have just been described, of securing the juices of cane by pressure
and of determining the sugars therein, do not give the actual
percentage of sugar in the cane. An approximate result may be secured
by assuming that the cane is composed of ninety parts of juice and
ten parts of cellular tissues and other insoluble matters. This
assumption is approximately true in most cases, but there are often
conditions arising which render the data calculated on the above
assumption misleading. In any particular case in order to be certain
that the correct percentage of sugar is secured it will be necessary
to determine the fiber in the cane. This is an analytical process of
considerable labor and especially so on account of the difficulty of
securing samples which represent the average composition of the cane.
The fibrous structure of the canes, the hardness of their external
covering and the toughness of their nodes or joints render the
sampling extremely difficult. Moreover, the content of sugar varies
in different parts of the cane. The parts nearest the ground are,
as a rule, richer than the upper joints and this is especially true
of sugar cane. In order, therefore, to get a fair sample, even of a
single cane, all parts of it must be considered. Several methods of the
direct determination of sugar in canes have been proposed and will be
described below.
[Illustration: FIGURE 65. MACHINE FOR CUTTING CANES.]
=211. Methods of Cutting or Shredding the Cane for Analytical
Purposes.=—A simple method of cutting canes into small pieces which
will permit of an even sampling is very much to be desired. The
cutting apparatus shown in Fig. 65 has been long in use in this
laboratory. The canes by it are cut into thin slices, but the cutting
edge of the knife being perpendicular to the length of the cane renders
the use of the instrument somewhat laborious and unsatisfactory. A
considerable time is required to cut a single cane and the slices which
are formed should be received in a vessel which will protect them as
much as possible from evaporation during the process of the work.
Instead of the apparatus above a small cane cutting machine arranged
with four knives on a revolving disk maybe used. The apparatus is shown
in Fig. 66. The cane is fed against the knives through the hole shown
in the open front of the apparatus and the knives thus strike the cane
obliquely.[179] The knives can be set in the revolving disk at any
desired position so as to cut the canes into chips as fine as may be
desired. The cossettes furnished by this method may be sampled directly
for the extraction of the sugar. In the case of the cossettes from
both instruments described above a finer subdivision may be secured by
passing them through a sausage cutter.
[Illustration: FIGURE 66. CANE CUTTING MILL.]
The best method for shredding canes, however, is to pass them through
the apparatus described on page 9. That machine gives an extremely
fine, moist mass, which is of uniform nature and capable of being
directly sampled.
=212. Methods of Determination.=—Even the finely divided material
obtained by the machine just described is not suited to give an
instantaneous diffusion for polarization as is done by the finely
ground beet pulp to be described further on. For the determination of
sugar a proper weight of the cossettes or pulp obtained as described
above, taken after thorough mixing, is placed in a flask graduated
properly and treated with water.[180]
The flask in which the mixture takes place should be marked to
compensate for the volume of the fiber of the cane. When the normal
weight of cane is taken for the ventzke scale, _viz._, 26.048, the
flask should be graduated at 102.6 cubic centimeters. If double the
normal weight be taken, the flask should be graduated at 205.2 cubic
centimeters. This graduation is based on the assumption of the presence
of fiber amounting to ten per cent of the weight of the cossettes. The
fiber is so nearly the density of the juice obtained as to be regarded
as one gram equal to one cubic centimeter. The flask is at first filled
almost full of water and then warmed to near the boiling point for an
hour with frequent shaking. It is then filled to a little above the
mark, the contents well mixed and warmed for ten minutes more with
frequent shaking. After cooling, the volume is made up to the mark,
well shaken and poured upon a filter. The filtrate is collected in a
sugar flask marked at fifty and fifty-five cubic centimeters. When
filled to the first mark a proper quantity of lead subacetate is added,
the volume completed to the second mark with water, the contents of the
flask well shaken, poured upon a filter and the filtrate polarized in
the usual way.
The reducing sugar is determined in an aliquot part of the filtrate by
one of the alkaline copper methods.
=213. Determination by Drying and Extraction.=—Instead of the diffusion
and polarization method just described, the fine pulp obtained may
be dried, the dried residue ground in a drug mill and extracted with
aqueous alcohol or with water.
To facilitate the calculation when this method is employed, the water
content of a small portion of the well sampled pulp is determined. The
rest of the pulp is dried, first for a few hours at a temperature not
above 60° or 70°, and then at the temperature of boiling water, either
in the open air or a partial vacuum, until all the water is driven off.
The dried residue can then be preserved in well stoppered bottles for
the determination of sugar at any convenient period. The finely ground
dried residue for this purpose is placed in an extraction apparatus
and thoroughly exhausted with eighty per cent alcohol. The extract is
dried and weighed, giving the total weight of all sugars present. After
weighing, the extract is dissolved in water, made up to a definite
volume and the reducing sugars determined in an aliquot portion thereof
by the usual methods. The weight of reducing sugars found, calculated
for the whole extract deducted from the total weight of this extract
will give the weight of the sucrose in the sample. From this number the
content of sugar in the original cane is determined from the percentage
of water found in the original sample.
_Example._—In a sample of finely pulped canes the content of water is
found to be 76.5 per cent. The thoroughly dried pulp is ground and
extracted with aqueous alcohol. Five grams give two and five-tenths
grams of the extract. The extract is dissolved in water, made up to
a definite volume and the reducing sugars determined in an aliquot
part and calculated for the whole, amounting to 150 milligrams. The
extract is therefore composed of 2.35 grams of sucrose and 0.15 gram
of reducing sugars. The calculation is now made to the original sample
which contained 76.5 per cent of water and 23.5 per cent of dry matter,
as follows: