Part 44

=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.

=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:

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.

=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.

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.

=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. 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.

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.

=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.

=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.

=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