203. Introduction.—In the preceding part directions have been given for the estimation of sugars and starches in approximately pure forms. In the present part will be described the most approved methods of separating these bodies and other carbohydrates from crude agricultural products and for their chemical examination. In many respects the processes which in a small way are used for preparing samples for analysis are employed on a large scale for technical and manufacturing purposes. It is evident, however, that the following paragraphs must be confined strictly to the analytical side of the question inasmuch as anything more than mere references to technical processes would lead into wide digressions.

In the case of sugars the analyst is for the most part quite as much in need of reliable methods of extraction and preparation as of processes for analysis. With starches the matter is more simple and the chief methods of separating them for examination were necessarily described in the previous part.

Sugars in fresh plants exist almost entirely in solution. This is true of all the great sources of the sugar of commerce, viz., the palm, the maple, the sugar beet and sugar cane. This statement is also true of fruits and the natural nectar of flowers. By natural or artificial drying the sugar may be reduced to the solid or semisolid state as in the cases of raisins and honey. In certain seeds, deficient in water, sugars may possibly exist in a solid state naturally, as may be the case with sucrose in the peanut and raffinose in cotton seed.

Starches on the other hand when soluble, are probably not true starches, but they partake more or less of a dextrinoid nature. Fine starch particles occur abundantly in the juices of some plants, as for instance sorghum, where they are associated with sugar and can be obtained from the expressed juice by subsidence. But even in such a case it is not certain that the starch enters into the general circulation. It is more likely formed locally by biochemical condensation of its constituents. Starches in a soluble or semisoluble state are transported, as a rule, to the tubers or seeds of plants where they are accumulated in large quantities as a reserve food for future growth. For a study of the plant metabolism whereby starch is produced and for its histological and physiological properties the reader may consult the standard authorities on vegetable physiology.[170]

204. Sugar in the Sap of Trees.—Many trees at certain seasons of the year, carry large quantities of sugar in their sap. Among these the maple and sugar palm are preeminent. The sap is secured by cutting a pocket into the side of the tree or by boring into it and allowing the sap to run into an appropriate receptacle through a spile. The content of sugar in the sap of the maple and palm varies greatly. In some cases it falls as low as one and a half and in others rises to as much as six or seven per cent.[171] In most cases the sugar in the maple sap is pure sucrose, but towards the end of the flowing season it may undergo changes of a viscous nature due to fermentation, or inversion, forming traces of invert sugar. In this country the sap of the maple may flow freely on any warm day in winter, but the sugar season proper begins about February 15th in Southern Ohio and Indiana, and about March 25th in Vermont. It lasts from six weeks to two months. The sap flows best during moderately warm, still days, after a light freeze.

In addition to sugar the maple sap contains a trace of albuminoid matters and some malic acid combined with lime. As a rule it can be subjected to polarization without preliminary clarification.

205. Determination of Sugar in Saps.—In most cases the sap may be directly polarized in a 200 millimeter tube. Its specific gravity is obtained by a spindle or pyknometer, and the percentage of sugars taken directly from the table on page 73, the degree brix corresponding to the sugar percentage.

On polarizing, the sugar percentage is calculated as follows:

Multiply the specific gravity of the sap by 100 and divide the product by 26.048. Divide the direct reading of the sap on the sugar scale by the quotient obtained above, and the quotient thus obtained will be the correct percentage of sugar in the original solution.

The formula is applicable for those instruments in which 26.048 grams represent the normal quantity of sugar which in 100 cubic centimeters reads 100 divisions on the scale. When other factors are used they should be substituted for 26.048 in the above formula.

The principle of the calculation is based on the weight of the sap which is contained in 100 cubic centimeters, and this is evidently obtained by multiplying 100 by the specific gravity of the sap. Since 26.048 is the normal quantity of sugar in that volume of the solution the quotient of the actual weight divided by that factor shows how many times too great the observed polarization is. The simple division of the polariscope reading by this factor gives the correct reading.

Example: Let the specific gravity of the sap be 1.015 and the observed polarization be 15.0. Then the true percentage of sugar in the sap is found by the equation:

101.5 : 26.048 = 15.0 : x.

Whence x = 3.85 = percentage of sugar in the sap.

The process outlined above is not applicable when a clarifying reagent such as lead subacetate or alumina cream must be used. But even in these cases it will not be found necessary to weigh the sap. A sugar flask graduated at 100 and 110 cubic centimeters is used and filled to the first mark with the sap, the specific gravity of which is known. The clarifying reagent is added, the volume completed to the second mark with water, and the contents of the flask well shaken and thrown on a dry filter. The observation tube, which should be 220 millimeters in length, is then filled with the clear filtrate and the rest of the process is as described above. A 200 millimeter tube may also be used in this case and the observed reading increased by one-tenth.

206. Estimation of Sugar in the Sap of Sugar Cane and Sorghum.—In bodies like sugar cane and sorghum the sap containing the sugar will not flow as in the cases of the maple and sugar palm. The simplest way of securing the sap of the bodies named is to subject them to pressure between rolls. A convenient method of obtaining the sap or juice is by passing the cane through a small three-roll mill indicated in the figure. Small mills of this kind have been used in this division for many years and with entire satisfaction. Small canes, such as sorghum, may be milled one at a time, or even two or three when they are very small. In the case of large canes, it is necessary that they be split and only half of them used at once. The mill should not be crowded by the feed in such a way as to endanger it or make it too difficult for the laborer to turn. From fifty to sixty per cent of the weight of a cane in juice may be obtained by passing it through one of these small mills. Experience has shown that there is a little difference between the juice as first expressed and the residual sap remaining in the bagasse, but the juice first expressed may be used for analysis for control purposes as a fair representative of all that the cane contains.

To determine the percentage of juice expressed, the canes may be weighed before passing through the mill and the juice collected. Its weight divided by the weight of the original cane will give the per cent of the juice expressed, calculated on the whole cane. Instead of weighing the juice the bagasse may also be collected and weighed; but on account of the rapidity with which it dries the operation should be accomplished without delay. The expressed juice is clarified with lead subacetate, filtered and polarized in the manner described in former paragraphs. Instead of weighing the juice, its specific gravity may be taken by an accurate spindle and the volume of it, equivalent to a given weight, measured from a sucrose pipette.[172]

A sucrose pipette for cane juice has a graduation on the upper part of the stem which enables the operator to deliver double the normal weight for the polariscope used, after having determined the density of the juice by means of a spindle. A graduation of from 5° to 25° of the brix spindle will be sufficient for all variations in the density of the juice, or one covering a range of from 10° to 20° will suffice for most instances. The greater the density of the juice the less volume of it will be required for the weight mentioned. For general use, the sucrose pipette is graduated on the stem to deliver from forty-eight to 50.5 cubic centimeters, the graduations being in terms of the brix spindle. The graduation of the stem of this instrument is shown in the accompanying figure. In the use of the pipette it is only necessary to fill it to the degree on the stem corresponding to the degree brix found in the preliminary trial.

The quantities of juice corresponding to each degree and fractional degree of the brix spindle are given in the following table; calculated for the normal weight 26.048 grams for the ventzke and for 16.19 grams for the laurent scale. The measured quantities of juice are placed in a 100 cubic centimeter sugar flask, treated with the proper quantity of lead subacetate, the volume completed to the mark, and the juice filtered and polarized in a 200 millimeter tube. The reading of the polariscope is divided by two for the factor 26.048 and by three for the factor 16.19.

Table for Use of Sucrose Pipettes.

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]

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.

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.

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:

5 : x :: 23.5 : 100, whence x = 21.27,

the weight of the original material corresponding to five grams of the dry substance. The original composition of the sample is therefore expressed by the following numbers:

214. Examination of the Bagasse.—The method just described for the examination of canes may be also applied to the analysis of bagasses, with the changes made necessary by the increased percentage of fiber therein. On account of the large surface exposed by the bagasse, the sampling, shredding and weighing should be accomplished as speedily as possible to avoid loss of moisture.

The optical examination of bagasses is rendered difficult by reason of the uneven pressure to which the canes are subjected. With fairly good milling in technical work the bagasses will have at least thirty per cent of fiber. The method for the polariscopic examination is therefore based upon that assumption, but the volume of the solution must be changed for varying percentages of fiber in the bagasse. On account of the smaller percentage of sugar, it is convenient to take double or three times the normal weight of the bagasse for examination. Since large sugar flasks are not commonly to be had the diffusion of the bagasse may be conducted in a quarter liter flask. In a quarter liter flask place 52.096 grams of the finely shredded bagasse, very nearly fill the flask with water and extract the sugar as described for canes in the foregoing paragraphs. In the weight of bagasse used there will be, in round numbers, fifteen grams of fiber. When the volume of water is completed to the mark the actual content of liquid in the flask will therefore be only 235 cubic centimeters. Fifty cubic centimeters of the filtrate are placed in a sugar flask marked at fifty and fifty-five cubic centimeters, the proper quantity of lead subacetate solution added, the volume completed to the upper mark, the contents of the flask well shaken, filtered and polarized in a 200 millimeter tube. Let the reading obtained be four degrees and increase this by one-tenth for the increased volume of solution above fifty cubic centimeters. The true reading is therefore four degrees and four-tenths. This reading, however, must be corrected, because the original volume instead of being 200 cubic centimeters, is 235 cubic centimeters. The actual percentage of sugar in the sample examined is obtained by the following proportion:

200 : 235 = 4.4 : x.

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.

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.

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]

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]