The correct reading is therefore 5°.2, the percentage of sugar in the
sample examined.
The results obtained by the method just described may vary somewhat
from the true percentage by reason of the variation of the content
of fiber in the bagasse. It is, however, sufficiently accurate for
technical control in sugar factories and on account of its rapidity
of execution is to be preferred for this purpose. More accurate
results would be obtained by drying the bagasse, and proceeding with
the examination in a manner entirely analogous to that described for
the extraction of sugar from dried canes by aqueous alcohol. In both
instances the reducing sugar is determined in the manner already
mentioned.
=215. Determination of Fiber in Cane.=—In estimating the content
of sugar in canes by the analysis of the expressed juices, it is
important to make frequent determinations of the fiber for the purpose
of obtaining correct data for calculation. In periods of excessive
drought, or when the canes are quite mature, the relative content of
fiber is increased, while, on the other hand, in case of immature
canes, or during excessive rainfalls, it is diminished. The chief
difficulty in determining the content of fiber in canes is found in
securing a representative sample. On account of the hard and fibrous
nature of the envelope and of their nodular tissues, canes are reduced
to a fine pulp with great difficulty by the apparatus in ordinary
use. A fairly homogeneous pulp, however, may be obtained by means of
the shredder described on page 9. The canes having been shredded as
finely as possible, a weighed quantity is placed in any convenient
extraction apparatus and thoroughly exhausted with hot water. The
treatment with hot water should be continued until a few drops of the
extract evaporated on a watch glass will leave no sensible residue.
The residual fiber is dried to constant weight at the temperature of
boiling water, cooled in a desiccator and rapidly weighed and the
percentage of fiber calculated from the data obtained. On account of
the great difficulty of securing a homogeneous pulp, even with the best
shredding machines, the determination should be made in duplicate or
triplicate and the mean of the results entered as the percentage of
fiber. The term fiber as used in this sense, must not be confounded
with the same term employed in the analysis of fodders and feeding
stuffs. In the latter case the term is applied to the residue left
after the successive treatment of the material with boiling, dilute
acid and alkali. The analysis of canes for feeding purposes is
conducted in the general manner hereinafter described for fodders.
=216. Estimation of Sugar in Sugar Beets.=—The methods employed for
the determination of the sugar content of beets are analogous to those
used for canes, with such variations in the method of extraction as are
made possible and necessary by the difference in the nature of these
sacchariferous plants. The sugar beet is more free of fiber and the
hard and knotty substances composing the joints of plants are entirely
absent from their composition. For this reason they are readily
reduced to a fine pulp, from which the sugar is easily extracted.
The analytical processes are also greatly simplified by the complete
absence of reducing sugars from the juices of healthy beets. The only
sugar aside from sucrose which is present in these juices is raffinose,
and this is not found in healthy beets, except when they have been
injured by frost or long keeping. In practical work, therefore, the
determination of sucrose completes the analysis in so far as sugars are
concerned. Four methods of procedure will illustrate all the principles
of the various processes employed.
=217. Estimation of Sucrose in the Expressed Juice.=—In the first
method the beets are reduced by any good shredding machine, to a fine
pulp, which is placed in a press and the juice expressed. In this
liquor, after clarification with lead subacetate, the sucrose is
determined by the polariscope. The methods of measuring, clarifying and
polarizing are the same as those described for saccharine juices in
paragraphs =83-85=. The mean percentage of juice in the sugar beet is
ninety-five. The corrected polariscopic reading obtained multiplied by
0.95 will give the percentage of sugar in the beet.
_Example._—The solids in a sample of beet juice, as measured by a brix
spindle, are 17.5 per cent. Double the normal weight of the juice is
measured from a sucrose pipette, placed in a sugar flask, clarified,
the volume completed to 100 cubic centimeters, the contents of the
flask well shaken and filtered. The polariscopic reading obtained is
29°.0. Then (29.0 ÷ 2) × 0.95 = 13.8 = percentage of sucrose in the
beet.
=218. Instantaneous Diffusion.=—In the second process employed for
determining the sugar content of beets, the principle involved depends
on the use of a pulp so finely divided as to permit of the almost
instant diffusion of the sugar present throughout the added liquid.
This diffusion takes place even in the cold and the process thus
presents a convenient and rapid method for the accurate determination
of the percentage of sugar in beets. The pulping is accomplished by
means of the machine described on page 10, or the one shown in Fig. 67.
The beet is pressed against the rapidly revolving rasp by means of the
grooved movable block and the finely divided pulp is received in the
box below. These machines afford a pulp which is impalpable and which
readily permits an almost instantaneous diffusion of its sugar content.
[Illustration: FIG. 67. APPARATUS FOR PULPING BEETS.]
=219. Pellet’s Method of Cold Diffusion.=—The impalpable pulp having
been obtained, by one of the processes described, the content of sugar
therein is determined as follows:[181]
A normal or double normal quantity of the pulp is quickly weighed,
to avoid evaporation, in a sugar dish with an appropriate lip, and
washed into the flask, which should be graduated, as shown in Fig. 68,
to allow for the volume of the fiber or marc of the beet. Since the
beet pulp contains, on an average, four per cent of marc, the volume
which is occupied thereby is assumed to be a little more than one cubic
centimeter. Since it is advisable to have as large a volume of water
as convenient, it is the practice of Pellet to wash the pulp into a
flask graduated at 201.35 cubic centimeters. If a 200 cubic centimeter
flask be used, the weight of the pulp should be 25.87 instead of
26.048 grams. After the pulp is washed into the flask, about six cubic
centimeters of lead subacetate of 30° baumé are added, together with a
little ether, to remove the foam. The flask is now gently shaken and
water added to the mark and the contents thoroughly shaken. If the pulp
is practically perfect, the filtration and polarization may follow
immediately. The filter into which the contents of the flask are poured
should be large enough to hold the whole quantity. It is recommended
to add a drop or two of strong acetic acid just before completing
the volume of the liquid in the flask to the mark. The polarization
should be made in a 400 millimeter tube, which will give directly the
percentage of sugar present. It is not necessary to heat the solution
in order to insure complete diffusion, but the temperature at which the
operation is conducted should be the ordinary one of the laboratory.
In case the pulp is not as fine as should be, the flask should be
allowed to stand for half an hour after filling, before filtration.
An insufficient amount of lead subacetate may permit some rotatory
bodies other than sugar to pass into solution, and care should be
taken to have always the proper quantity of clarifying material added.
The presence of these rotating bodies, mostly of a pectic nature,
may be shown by extracting the pulp first with cold water until all
the sugar is removed, and afterwards with boiling water. The liquor
obtained from the last precipitation will show a decided right-handed
rotation, unless first treated with lead subacetate, in which case
the polarization will be zero. A very extended experience with the
instantaneous cold aqueous diffusion has shown that the results
obtained thereby are quite as reliable as those given by hot alcoholic
or aqueous digestion.
=220. Flask for Cold Diffusion and Alcohol Digestion.=—For convenience
in washing the pulp into the sugar flask, the latter is made with
an enlarged mouth as shown in Fig. 68. The dish holding the weighed
quantity of pulp is held with the lip in the mouth of the flask, and
the pulp washed in by means of a jet of water furnished from a pressure
bottle or washing flask. The flask shown is graduated for the normal
weight of pulp, _viz._, 26.048 grams. The marking is on the constricted
neck and extends from 100 to 101.3 cubic centimeters. This permits
of making the proper allowance for the volume occupied by the marc
or fiber, but this is unnecessary for the usual character of control
analyses. In the case of healthy, fresh beets, the volume occupied
by the marc is nearly one and three-tenths cubic centimeters for the
normal polariscopic weight of 26.048 grams of pulp. For the laurent
instrument this volume is nearly one cubic centimeter.
[Illustration: FIGURE 68. APPARATUS FOR COLD DIFFUSION.]
=221. Extraction with Alcohol.=—The third method of determining sugar
in beets is by alcoholic extraction. The principle of the method is
based on the fact that aqueous alcohol of not more than eighty per
cent strength will extract all the sugar from the pulp, but will not
dissolve the pectic and other rotatory bodies, which, in solution,
are capable of disturbing the rotatory power of the sugar present.
It is also further to be observed that the rotatory power of pure
sucrose, in an aqueous alcoholic solution, is not sensibly different
from that which is observed in a purely aqueous liquid. The pulp,
which is to be extracted, should be in as fine a state of subdivision
as convenient, and the process may be carried on in any of the forms
of extraction apparatus already described, or in the apparatus shown
in Fig. 69. The extraction tube, of the ordinary forms of apparatus,
however, is scarcely large enough to hold the required amount of pulp,
and therefore special tubes and forms of apparatus have been devised
for this method of procedure. In weighing the pulp for extraction,
a quarter, half, or the exact amount required for the polariscope
employed, should be used. If the tubes are of sufficient size the full
weight may be taken, _viz._, 26.048 or 16.19 grams for the instruments
in ordinary use. Since the pulp contains a large quantity of water,
the extraction could be commenced with alcohol of standard strength,
_viz._, about ninety-five per cent. The volume of alcohol employed
should be such as will secure a strength of from seventy to eighty
per cent when mixed with the water contained in the pulp. The flask
receiving the extract should be kept in continuous ebullition and the
process may be regarded as complete in about one hour, when the pulp
has been properly prepared. The method of extracting beet pulp with
alcohol is due to Scheibler, and in its present form the process is
conducted according to the methods described by Scheibler, Sickel, and
Soxhlet.[182]
[Illustration: FIG. 69. SICKEL-SOXHLET EXTRACTOR.]
If the pulp be obtained by any other means than that of a fine rasp,
the extraction of the sugar by the aqueous alcohol takes a long time,
and even a second extraction may be necessary. It is convenient to use
as a flask for holding the solvent, one already graduated at 100 or 110
cubic centimeters. A flask especially constructed for this purpose, has
a constricted neck on which the graduations are made, and a wide mouth
serving to attach it to the extracting apparatus, as shown in Fig.
68. When the extract is obtained in this way, it is not necessary to
transfer it to a new flask before preparing it for polarization. When
the extraction is complete, the source of heat is removed, and when all
the alcohol is collected in the flask, the latter is removed from the
extraction apparatus, cooled to room temperature, a sufficient quantity
of lead subacetate added, the flask well shaken, the volume completed
to the mark with water, again well shaken and the contents of the
flask thrown upon the filter. It is important to avoid loss of alcohol
during filtration. For this purpose it is best to have a folded filter
and to cover the funnel immediately after pouring the contents of the
flask upon the filter paper, with a second larger funnel. The stem of
the funnel carrying the filter paper, should dip well into the flask
receiving the filtrate. As in other cases of filtering sugar juices for
polarization, the first portions of the filtrate received should be
rejected. The percentage of sugar is obtained in the filtrate in the
usual way.
Where a weight of pulp equal to the normal factor of the polariscope
employed is used, and the extract collected in a 100 cubic centimeter
flask, the percentage of sugar is directly obtained by making the
reading in a 200 millimeter tube. With other weights of pulp, or other
sizes of flask, the length of the observation tube may be changed or
the reading obtained corrected by multiplication or division by an
appropriate factor. A battery of sickel-soxhlet extractors is shown in
Fig. 69.[183]
[Illustration: FIG. 70.]
=222. Scheibler’s Extraction Tube.=—In order to secure a speedy
extraction of large quantities of pulp, Scheibler recommends the use of
the extraction tube shown in Fig. 70.[184] The apparatus is composed of
three concentric glass cylinders. The outer and middle cylinders are
sealed together at the top, and the inner one is movable and carries
a perforated diaphragm below, for filtering purposes. Near the top it
is provided with small circular openings, whereby the alcoholic vapors
may gain access to the condenser (not shown). The middle cylinder is
provided with two series of apertures, through the higher of which the
vapor of alcohol passes to the condenser, while the alcohol which has
passed through the pulp and collected between the inner and middle
cylinders, flows back through the lower into the flask (not shown)
containing the boiling alcohol.
The middle cylinder is provided with a curved bottom to prevent the
filtering end of the inner tube from resting too tightly against it.
The tube containing the pulp is thus protected from the direct heat
of the alcoholic vapors during the progress of extraction by a thin
cushion of liquid alcohol.
=223. Alcoholic Digestion.=—The fourth method of determining sugar in
beet pulp, is by means of digestion with hot alcohol. The principle
of this method is precisely the same as that which is involved in
aqueous diffusion in the cold. The diffusion, however, in the case of
the alcohol, is not instantaneous, but is secured by maintaining the
mixture of the pulp and alcohol for some time at or near the boiling
point. The methods of preparing the pulp, weighing it and introducing
it into the digestion flask are precisely those used for aqueous
digestion, but in the present case a somewhat coarser pulp may be
employed. The method is commonly known as the rapp-degener process.[185]
Any convenient method of heating the alcohol may be used. In this
laboratory the flasks are held on a false bottom in a bath composed of
two parts of glycerol and one of water. One side of the bath holder
is made of glass, as shown in Fig. 71, in order to keep the flasks in
view. In order to avoid the loss of alcohol, the digestion flask should
be provided with a reflux condenser, or be attached to an ordinary
condenser, which will reduce the vapors of alcohol again to a liquid.
Unless the weather be very warm, the reflux condenser may consist of
a glass tube of rather wide bore and at least one meter in length, as
shown in Fig. 71. A slight loss of alcohol during the digestion is of
little consequence. A convenient method of procedure is the following.
Double the quantity of the beet pulp required for the ventzke
polariscope, _viz._, 52.096 grams, weighed in a lipped metal dish,
is washed, by means of alcohol, into a flask marked at 202.6 cubic
centimeters, and the flask filled two-thirds with ninety-five per
cent alcohol and well shaken. Afterwards, a proper quantity of lead
subacetate is added, and then sufficient alcohol to complete the volume
to the mark. The flask is then attached to the condenser, placed in
a water-glycerol bath and heated to a temperature of 75° for about
forty-five minutes. At the end of this time, the flask is removed from
the bath and condenser, cooled quickly with water, alcohol added to
the mark and well shaken. The filtration should be accomplished with
precautions, to avoid the loss of alcohol mentioned in paragraph =221=.
The filtrate is examined in the polariscope in a 200 millimeter tube,
and the reading obtained gives directly the percentage of sugar in the
sample examined. Half the quantity of pulp mentioned, in a 101.3 cubic
centimeter flask, may also be used. A convenient form of arranging a
battery of flasks is shown in the accompanying figure.
[Illustration: FIG. 71. BATTERY FOR ALCOHOLIC DIGESTION.]
=224. Determination of Sugar in Mother Beets.=—In selecting mother
beets for seed production, it is necessary to secure only those of a
high sugar content. This is accomplished by boring a hole about two and
a half centimeters in diameter obliquely through the beet by means of
the apparatus shown in Fig. 72.
The beet is not injured for seed production by this process, and the
pulp obtained is used for the determination of sugar. The juice is
expressed by means of the small hand press shown in Fig. 73. Since only
a small quantity of juice is obtained, it is advisable to prepare it
for polarization in a sugar flask marked at fifty cubic centimeters.
The density of the juice, by reason of its small volume, is easiest
obtained by the hydrostatic balance, as described in paragraph =53=.
In lieu of this, the juice may be quickly weighed in a counterbalanced
dish on a balance giving results accurate to within one milligram. The
rest of the analytical process is similar to that already described.
[Illustration: FIG. 72. RASP FOR SAMPLING MOTHER BEETS.]
[Illustration: FIG. 73. HAND PRESS FOR BEET ANALYSIS.]
[Illustration: FIG. 74.]
=225. Aqueous Diffusion.=—The process of instantaneous aqueous
diffusion may also be applied to the examination of mother beets. For
this purpose the beets are perforated by a rasp, devised by Keil, shown
lying on the floor in Fig. 72, the characteristics of which are shown
in Fig. 74. The conical end of the rasp is roughened in such a way
as to reduce the beet to an impalpable pulp. This end is fastened by
a bayonet fastening to the cylindrical carrier or arm in such a way
that, by means of a groove in the conical end of the rasp, the pulp is
introduced into the cylinder. The cylinder is provided with a small
piston by means of which the pulp can be withdrawn when the cylindrical
portion of the rasp is detached from the driving machinery. It is
important that the rasp be driven at a high rate of speed, _viz._, from
1500 to 2000 revolutions a minute. The sample of pulp at this rate of
revolution is taken almost instantly, and with skilled manipulators the
whole operation of taking a sample, removing the rasp by means of its
bayonet fastenings, withdrawing the sample of pulp and replacing the
rasp ready for another operation does not consume more than from ten
to twenty seconds. From three to four samples may thus be taken in a
minute. The samples of pulp as taken are dropped into numbered dishes
corresponding to the numbers on the beets. One-quarter of the normal
weight for the polariscope is used for the analysis. The pulp is placed
in a fifty cubic centimeter flask, water and lead subacetate added, the
flask well shaken, filled to the mark with water, again well shaken,
the contents thrown on the filter, and the filtrate polarized in a 400
millimeter tube, giving the direct percentage of sugar. For practical
purposes the percentage of marc in the beet may be neglected. If the
polarization take place in a 200 millimeter tube the number obtained
should be multiplied by two for the content of sugar.
In numbering sugar beets which are to be analyzed for seed production,
it is found that a small perforated tin tag bearing a number may be
safely affixed to the beet by means of a tack. It is not safe to use
paper tags as they may become illegible by becoming wet before the
sorting of the beets is completed. Where from 1000 to 2000 beets
are to be examined in a day, the number of the beets and the dishes
corresponding thereto must be carefully controlled to avoid confusion
and mistakes.
=226. Determination of Sugars without Weighing.=—An ingenious device
for the rapid analysis of mother beets is based upon the use of a
machine which cuts from the beet a core of given dimensions and this
core is subsequently reduced to a pulp which is treated with cold water
and polarized in the manner described above. The cutting knives of the
sampler can be adjusted to take a core of any desired size. Since the
beets used for analysis have essentially the same specific gravity, the
cores thus taken weigh sensibly the same and the whole core is used
for the analysis, thus doing away with the necessity of weighing. The
core obtained is reduced to a pulp in a small machine so adjusted as
to permit the whole of the pulp, when prepared, to be washed directly
into the sugar flask. By the use of this machine a very large number of
analyses can be made in a single day, and this is highly important in
the selection of mother beets, for often 50,000 or 100,000 analyses are
to be made in a short time.
[Illustration: FIG. 75. TUBE FOR CONTINUOUS OBSERVATION.]
=227. Continuous Diffusion Tube.=—To avoid the delay occasioned by
filling and emptying observation tubes in polariscopic work, where
large numbers of analyses of canes and beets are to be made, Pellet
has devised a continuous diffusion tube, by means of which a solution,
which has just been observed, is rapidly and completely displaced by a
fresh solution. This tube, improved by Spencer, is shown in Fig. 75.
The fresh solution is poured in at the funnel, displacing completely
the old solution which flows out through the tube at the other end.
The observer watches the field vision and is able to tell when the
old solution is completely displaced by the clearing of the field, at
which time the reading of the new solution can be quickly made. When
solutions are all ready for examination an expert observer can easily
read, by the aid of this device, from four to five of them in a minute.
=228. Analysis of Sirups and Massecuites.=—The general principles which
control the analysis of sirups and massecuites are the same whether
these products be derived from canes or beets. In the case of the
products of canes, the sirups or massecuites contain chiefly sucrose,
invert sugar, and other copper reducing bodies, inorganic matters and
water. In the case of products derived from sugar beets the contents
are chiefly sucrose, inorganic matters, a trace of invert sugar,
raffinose and water. The principles of the determination of these
various constituents have already been described.
=229. Specific Gravity.=—The specific gravity of sirups and molasses
can be determined by the spindle in the usual way, but in the case of
molasses which is quite dense, the spindle method is not reliable. It
is better, therefore, both in molasses and massecuites, to determine
the density by dilution. For this purpose, as described by Spencer,
a definite weight of material, from 200 to 250 grams, is dissolved
in water and the volume of the solution completed to half a liter. A
portion of the solution is then placed in a cylinder and the quantity
of total solids contained therein determined in the usual way by a brix
or specific gravity hydrometer. In case 250 grams of the material be
used the calculation of the brix degree for the original material is
conducted according to the following formula:
G × _B_ × _V_
_x_ = -------------.
_W_
In the above formula _x_ is the required brix degree, _V_ the volume
of the solution, _B_ the observed brix degree of the solution, and G
the corresponding specific gravity obtained from the table on page 73.
When only small quantities of the material are at hand the hydrostatic
balance (=53=) should be employed. For this purpose twenty-five grams
of the material are dissolved in water and the volume of the solution
made up to 100 cubic centimeters. The sinker of the hydrostatic balance
is placed in the solution and equilibrium secured by placing the
weights upon the arm of the balance in the usual manner. Since the arm
of the balance is graduated to give, by direct reading, the specific
gravity, the density can be obtained at once.
_Example._—Let the position of the weights or riders upon the balance
arm be as follows:
(1) at point of suspension of the bob = 1.000
(3) at mark 7 on beam = 0.07
(4) at mark 9 on beam = 0.009
Specific gravity = 1.079
The nearest brix degree corresponding to this specific gravity (=58=)
is 19. The total weight of the solution is equal to 100 × 1.079,
_viz._, 107.9 grams. Since the solution contains nineteen per cent of
solid matter as determined by the hydrostatic balance, the total weight
of solid matter therein is 107.9 × 19 ÷ 100 = 20.5 grams. The total per
cent. of solid matter in the original sample is therefore 20.5 ÷ 25 ×
100 = 82 and the specific gravity corresponding thereto (page 74) is
1.42934.
The specific gravity of a massecuite may also be determined in
pyknometers especially constructed for this purpose.[186]
=230. Determination Of Water.=—The accurate determination of water
in sirups and massecuites is a matter of considerable difficulty.
The principles of conducting the process (=26=), applicable also to
the determination of water in honeys and other viscous liquids, are
as follows: In all cases where invert sugar is present the drying
should be conducted at a temperature not exceeding 75° or 80°. In
dense molasses and massecuites a weighed quantity should be dissolved
and made up to a definite volume and an aliquot portion taken for
the determination. In order to secure complete desiccation at a low
temperature, the drying should be accomplished in partial vacuum (pages
22, 23). The process of desiccation should be conducted in shallow,
flat-bottom dishes which may be conveniently and cheaply made of
aluminum and the process is hastened by filling the dish previously
with thoroughly dried fragments of pumice stone. When the sample does
not contain any invert sugar the desiccation can be safely accomplished
at the temperature of boiling water. Drying should be continued in all
cases until practically constant weight is obtained.
=231. Determination Of Ash.=—Ash is an important constituent of the
sirups, molasses, and massecuites from canes and exists in very much
larger quantities in the same products from beets. The ash may be
determined directly by careful incineration, but it is customary to add
a few drops of sulfuric acid, sufficient to combine with all the bases
present and be in slight excess. The presence of sulfuric acid is of
some advantage in the beginning of the carbonization and renders the
process somewhat easier of accomplishment. When sulfuric acid is used,
the weight of ash obtained must be diminished by one-tenth to allow for
the increased weight obtained by the conversion of the carbonates into
sulfates. In general, the principles and methods described on pages
36-40 are to be employed.
=232. Determination of Reducing Sugars in Sirups, Molasses, and
Massecuites.=—The quantity of reducing sugars in the products derived
from the sugar beet, as a rule, is insignificant. In the products from
sugar cane there are large quantities of reducing matters which, in
general, are determined by any of the standard methods already given.
It has been shown by the author[187] that the juices of healthy sugar
canes contain a small quantity of invert sugar, but this statement has
been contradicted by Bloufret.[188] It is certain, however, that the
reducing bodies derived from the products of manufacture of sugar cane
and sorghum deport themselves in a manner somewhat different from pure
invert sugar. In the absence of definite information in respect of the
constitution of these bodies, the methods applicable to dextrose and
invert sugar may be applied.
Since the paragraphs relating to these processes were printed some
important improvements in the preparation of the alkaline copper
solutions have been made. The copper carbonate solution, as has already
been said, is peculiarly suited to the determination of reducing sugars
in the presence of sucrose and the modified forms of this solution,
and the methods of employing them with invert sugar, dextrose,
levulose, and maltose, are described below.
=233. Estimation of Minute Quantities of Invert Sugar in Mixtures.=—The
method of Hiller and Meissl, paragraph =142=, may be used for the
estimation of small quantities of invert sugar in mixtures. A modified
form of Soldaini’s reagent is, however, to be preferred for this
purpose. Ost has proposed and tested a copper carbonate solution for
the purpose mentioned which gives reliable results.[189] The solution
has the following composition:
One liter contains 3.6 grams crystallized copper sulfate.
250.0 ” potassium carbonate.
100.0 ” hydrogen potassium sulfate.
This reagent undergoes no change when kept for a long while, especially
in large vessels. Even in smaller vessels it can be kept for a year or
more without undergoing any change.
The method of analysis is the same as that described in paragraph
=128=, with the exception that the boiling is continued for only five
minutes instead of ten, and the quantities of the copper and sugar
solutions used are doubled, being 100 and fifty cubic centimeters
respectively. In no case must the solution used contain more than
thirty-eight milligrams of invert sugar. The quantity of sucrose in the
mixture is obtained by polarization (=94=). Ost has also recalculated
the reduction values of the common sugars for the strong copper
carbonate solution, and the numbers obtained are slightly different
from those given on page 142.[190]
For different percentages of invert sugar in mixtures of sucrose, the
quantities of invert sugar are calculated from the number of milligrams
of copper obtained by the following table:
(A) = Milligrams of copper obtained.
(B) = Pure invert sugar.
(C) = Invert sugar.
(D) = Sucrose.
MILLIGRAMS OF INVERT SUGAR IN MIXTURES OF
5(C) 2(C) 1.5(C) 1.0(C) 0.8 (C) 0.6(C) 0.5(C)
(A) (B) 95(D) 98(D) 98.5(D) 99.0(D) 99.2 (D) 99.4(D) 99.5(D)
88 37.9 37.1 36.0 35.4 34.7 34.2 33.9 33.6
85 36.3 35.5 34.5 34.0 33.4 32.9 32.5 32.2
80 33.9 33.0 33.2 31.7 31.2 30.7 30.2 29.9
75 31.6 30.7 30.0 29.5 29.0 28.5 28.1 27.7
70 29.4 28.5 27.8 27.4 26.8 26.4 25.9 25.6
65 27.3 26.3 25.7 25.3 24.7 24.3 23.8 23.5
60 25.2 24.2 23.6 23.2 22.6 22.2 21.8 21.5
55 23.1 22.1 21.6 21.2 20.6 20.2 19.8 19.6
50 21.2 20.1 19.6 19.2 18.6 18.3 17.9 17.7
45 19.3 18.2 17.6 17.2 16.7 16.3 16.0 15.8
40 17.3 16.3 15.7 15.3 14.8 14.5 14.2 14.0
35 15.4 14.5 13.8 13.4 13.0 12.7 12.5 12.3
30 13.5 12.6 12.0 11.6 11.2 11.0 10.8 10.6
25 11.5 10.8 10.3 10.0 9.5 9.3 9.1 9.0
20 9.6 9.1 8.6 8.3 7.9 7.7 7.5 7.3
15 7.7 7.3 6.9 6.7 6.3 6.1 5.8 5.6
10 5.8 5.4 5.1 5.0 4.7 4.5 4.2 3.9
MILLIGRAMS OF INVERT SUGAR IN MIXTURES OF
0.4(C) 0.3(C) 0.2(C) 0.1(C) 0.05(C) 0.02(C)
(A) 99.6(D) 99.7(D) 99.8(D) 99.9(D) 99.95(D) 99.98(D)
88 33.3
85 32.0 31.8
80 29.7 29.5
75 27.4 27.2
70 25.3 25.0
65 23.2 22.8
60 21.2 20.8 20.4
55 19.3 18.9 18.5
50 17.4 17.0 16.7
45 15.6 15.3 14.9
40 13.8 13.5 13.2
35 12.1 11.9 11.5 10.3
30 10.4 10.2 9.9 8.8
25 8.8 8.6 8.2 7.3
20 7.1 6.9 6.6 5.8 4.9
15 5.4 5.2 5.0 4.4 3.7 2.0
10 3.8 3.5 3.4 3.0 2.5 1.7
=234. Soldaini’s Method Adapted to Gravimetric Work.=—By reason of
their better keeping qualities and because of their less energetic
action on non-reducing sugars, copper carbonate solutions are to be
preferred to the alkaline copper tartrate solutions for gravimetric
determinations of reducing sugars in cane juices and sugar house
products, provided the difficulties which attend the manipulation
can be removed. Ost has succeeded in securing perfectly satisfactory
results with copper carbonate solution by slightly varying the
composition thereof and continuing the boiling, for the reduction of
the copper, ten minutes.[191] The copper solution is made as follows:
17.5 grams crystallized copper sulfate.
250.0 ” potassium carbonate.
100.0 ” ” bicarbonate.
The above ingredients are dissolved in water and the volume of
the solution completed to one liter. The object of the potassium
bicarbonate is to secure in the solution an excess of carbon dioxid
and thus prevent the deposition of basic copper carbonate on keeping.
The manipulation is conducted as follows:
One hundred cubic centimeters of the copper solution are mixed with
half that quantity of the sugar solution in a large erlenmeyer, which
is placed upon a wire gauze, heated quickly to boiling and kept in
ebullition just ten minutes. The sugar solution should contain not
less than eighty nor more than 150 milligrams of the reducing sugar,
and the quantity of the solution representing this should be diluted
to fifty cubic centimeters before mixing with the copper solution.
After boiling, the contents of the erlenmeyer are quickly cooled and
filtered with suction through an asbestos filter and the whole of the
copper suboxid washed into the filter tube. This precipitated suboxid
is washed once with a little potassium carbonate solution then with hot
water and finally with alcohol, well dried, heated to redness, and the
copper oxid obtained reduced to metallic copper in an atmosphere of
hydrogen entirely free of arsenic. From the weight of metallic copper
obtained the quantity of sugar which has been oxidized is calculated
from the tables below.
It is evident that the process given above may be varied so as to
conform to the practice observed in this laboratory of cooling the
boiling solution sufficiently at once by adding to it an equal volume
of recently boiled, cold water, collecting the precipitated copper
suboxid in a gooch, and, after washing it, securing solution in nitric
acid and the precipitation of the copper by electrolysis.
TABLE SHOWING MILLIGRAMS DEXTROSE,
LEVULOSE AND INVERT SUGAR OXIDIZED,
CORRESPONDING TO MILLIGRAMS OF
COPPER REDUCED.
Copper. Dextrose. Levulose. Invert.
435 152.3 145.9 147.5
430 149.8 143.4 145.3
425 147.3 140.9 143.1
420 144.8 138.4 140.8
415 142.3 135.9 138.5
410 139.8 133.5 136.2
405 137.3 131.1 133.9
400 134.9 128.7 131.6
395 132.5 126.4 129.3
390 130.1 124.1 127.0
385 127.8 121.8 124.8
380 125.5 119.5 122.6
375 123.3 117.2 120.4
370 121.1 115.0 118.2
365 119.0 112.8 116.0
360 116.9 110.6 113.9
355 114.8 108.5 111.8
350 112.8 106.4 109.8
345 110.8 104.3 107.8
340 108.8 102.3 105.8
335 106.8 100.3 103.8
330 104.9 98.4 101.8
325 103.0 96.5 99.9
320 101.1 94.6 98.0
315 99.2 92.8 96.2
310 97.4 91.0 94.4
305 95.6 89.2 92.6
300 93.8 87.5 90.9
295 92.0 85.8 89.2
290 90.2 84.1 87.5
285 88.4 82.4 85.8
280 86.7 80.8 84.1
275 85.0 79.2 82.4
270 83.3 77.6 80.7
265 81.5 76.1 79.1
260 79.8 74.6 77.5
255 78.1 73.1 75.9
250 76.5 71.6 74.3
245 74.9 70.1 72.7
240 73.3 68.6 71.1
235 71.7 67.2 69.5
230 70.1 65.7 68.0
225 68.5 64.3 66.5
220 66.9 62.8 65.0
215 65.3 61.4 63.5
210 63.8 59.9 62.0
205 62.2 58.5 60.5
200 60.7 57.0 59.0
195 59.1 55.6 57.5
190 57.6 54.1 56.0
185 56.0 52.7 54.5
180 54.5 51.2 53.1
175 53.0 49.8 51.6
170 51.5 48.4 50.2
165 50.0 46.9 48.7
160 48.5 45.5 47.3
155 47.0 44.1 45.8
150 45.5 42.7 44.4
145 44.0 41.3 42.9
140 42.5 39.9 41.5
135 41.0 38.5 40.1
130 39.6 37.1 38.6
125 38.1 35.7 37.2
120 36.7 34.3 35.8
115 35.2 32.9 34.3
110 33.7 31.6 32.9
105 32.2 30.3 31.4
100 30.7 29.0 30.0
95 29.2 27.7 28.5
90 27.8 26.4 27.1
85 26.3 25.1 25.6
80 24.8 23.8 24.2
75 23.3 21.5 22.8
70 21.8 20.2 21.4