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.
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.
Fig. 72. Rasp for Sampling Mother Beets.
Fig. 73. Hand Press for Beet Analysis.
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.
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:
| x = | G × B × V |
| 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:
| 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.
Corresponding Table for Maltose.
| Milligrams copper obtained. |
Milligrams maltose anhydrid oxidized. |
Milligrams maltose hydrate oxidized. |
|---|---|---|
| 435 | 263.7 | 277.6 |
| 430 | 259.3 | 273.0 |
| 425 | 255.0 | 268.4 |
| 420 | 250.9 | 264.1 |
| 415 | 247.0 | 260.0 |
| 410 | 243.2 | 256.0 |
| 405 | 339.4 | 252.0 |
| 400 | 235.6 | 248.0 |
| 395 | 231.9 | 244.1 |
| 390 | 228.2 | 240.2 |
| 385 | 224.6 | 236.4 |
| 380 | 221.1 | 232.7 |
| 375 | 217.7 | 229.1 |
| 370 | 214.4 | 225.6 |
| 365 | 211.1 | 222.2 |
| 360 | 207.9 | 218.8 |
| 355 | 204.7 | 215.4 |
| 350 | 201.5 | 212.1 |
| 345 | 198.3 | 208.7 |
| 340 | 195.2 | 205.4 |
| 335 | 192.0 | 202.1 |
| 330 | 188.8 | 198.8 |
| 325 | 185.7 | 195.4 |
| 320 | 182.5 | 192.1 |
| 315 | 179.4 | 188.8 |
| 310 | 176.3 | 185.6 |
| 305 | 173.3 | 182.4 |
| 300 | 170.3 | 179.2 |
| 295 | 167.3 | 176.1 |
| 290 | 164.4 | 173.0 |
| 285 | 161.4 | 169.9 |
| 280 | 158.5 | 166.8 |
| 275 | 155.5 | 163.7 |
| 270 | 152.6 | 160.7 |
| 265 | 149.7 | 157.6 |
| 260 | 146.8 | 154.6 |
| 255 | 143.9 | 151.5 |
| 250 | 141.1 | 148.5 |
| 245 | 138.2 | 145.5 |
| 240 | 135.4 | 142.5 |
| 235 | 132.5 | 139.5 |
| 230 | 129.7 | 136.5 |
| 225 | 126.8 | 133.5 |
| 220 | 124.0 | 130.6 |
| 215 | 121.2 | 127.6 |
| 210 | 118.4 | 124.7 |
| 205 | 115.7 | 121.8 |
| 200 | 112.9 | 118.9 |
| 195 | 110.2 | 116.0 |
| 190 | 107.4 | 113.1 |
| 185 | 104.7 | 110.2 |
| 180 | 101.9 | 107.3 |
| 175 | 99.2 | 104.4 |
| 170 | 96.4 | 101.5 |
| 165 | 93.7 | 98.6 |
| 160 | 90.9 | 95.7 |
| 155 | 88.2 | 92.8 |
| 150 | 85.4 | 89.9 |
| 145 | 82.6 | 87.0 |
| 140 | 79.9 | 84.1 |
| 135 | 77.1 | 81.2 |
| 130 | 74.4 | 78.3 |
| 125 | 71.6 | 75.4 |
| 120 | 68.9 | 72.5 |
| 115 | 66.1 | 69.6 |
| 110 | 63.4 | 66.7 |
| 105 | 60.6 | 63.8 |
| 100 | 57.9 | 60.9 |
| 95 | 55.1 | 58.0 |
| 90 | 52.3 | 55.1 |
| 85 | 49.6 | 52.2 |
| 80 | 46.8 | 59.3 |
| 75 | 44.1 | 56.4 |
| 70 | 41.4 | 53.5 |
235. Weighing the Copper as Oxid.—In the usual methods of the determination of reducing bodies, the percentage is calculated either volumetrically from the quantity of the sugar solution required to decolorize a given volume of the alkaline copper solution, or the reduced copper suboxid is brought into a metallic state by heating in an atmosphere of hydrogen or by electrolytic deposition. A quicker method of procedure is found in completing the oxidation of the cupric oxid by heating to low redness in a current of air.[192] For this determination the precipitation of the cuprous oxid and its filtration are made in the usual manner. The cuprous oxid is collected in a filtering tube, made by drawing out to proper dimensions a piece of combustion tube, and has a length of about twelve centimeters in all. The unchanged part of the tube is about eight centimeters in length and twelve millimeters in diameter. It is filled by first putting in a plug of glass wool and covering this with an asbestos felt on top of which another plug of glass wool is placed. After the cuprous oxid is collected in the tube it is washed with boiling water, alcohol and ether. The rubber tube connecting it with the suction is of sufficient length to permit the tube being taken in one hand and brought into a horizontal position over a bunsen. The tube is gradually heated, rotating it meanwhile, until any residual moisture, alcohol or ether, is driven off from the filtering material. The layer of glass wool holding the cuprous oxid is gradually brought into the flame and as the oxidation begins the material will be seen to glow. The heating is continued for some time after the glowing has ceased, in all for three or four minutes, the tube and the copper oxid which it contains being brought to a low redness. The current of air passing over the red-hot material in this time oxidizes it completely. The filtering tube, before use, must be ignited and weighed in exactly the same manner as described above. The heat is so applied as not to endanger the rubber tube attached to one end of the filtering tube nor to burn the fingers of the operator as he turns the tube during the heating. After complete oxidation the tube is cooled in a desiccator and weighed, the increase of weight giving the copper oxid. For the atomic weights, 63.3 copper and 15.96 oxygen, one gram of copper oxid is equivalent to 0.79864 gram of copper, and for the weights 63.17 copper and 15.96 oxygen, one gram of copper oxid equals 0.79831 gram of copper. From the amount of metallic copper calculated by one of these factors, the reducing sugar is determined by the tables already given.
236. Estimation of Dry Substance, Polarization and Apparent Purity for Factory Control.—For technical purposes the methods of determining the above factors, proposed by Weisberg and applicable to concentrated sirups, massecuites, and molasses, may be used.[193] Five times the half normal quantity of the material, viz., 65.12 grams, are placed in a quarter liter flask, dissolved in water and the flask filled to the mark. In the well shaken mixture, which is allowed to stand long enough to be free of air, the degree brix is estimated by an accurate spindle. For example, in the case of molasses, let the number obtained be 18.8.
Fifty cubic centimeters of the solution are poured into a 100 cubic centimeter flask, the proper quantity of lead subacetate added, the flask filled to the mark with water, its contents filtered, and the filtrate polarized in a 200 millimeter tube. Let the number obtained on polarization be 22°.1. This number may be used in two ways. If it be multiplied by two the polarization of the original sample is obtained; in this case, viz., 44°.2. In the second place, if 44.2 be multiplied by 0.26048 and this product divided by the specific gravity corresponding to 18°.8. viz., 1.078, the quotient 10.68 is secured representing the polarization or per cent of sugar contained in the solution of which the degree brix was 18.8°. From the numbers 18.8 and 10.68 the apparent purity of the solution, 56.8, is calculated, viz., 10.68 × 100 ÷ by 18.8. The original product as calculated above gives a polarization of 44.2 and this number multiplied by 100 and divided by 56.8 gives 77.8, or the apparent percentage of dry matter. The original sample of molasses, therefore, had the following composition:
| Degree brix (total solids) | 77.8 | per cent. |
| Sucrose | 44.2 | ” |
| Solids, not sucrose | 33.6 | ” |
| Apparent purity | 56.8 | ” |
It is seen from the above that with a single weighing and a single polarization, and within from ten to fifteen minutes, all needful data in respect of the proper treatment of molasses for the practical control and direction of a factory can be obtained.
In case a laurent polariscope is used, five times the normal weight, viz., eighty-one grams of the raw material are used and the process conducted as above.
237. Occurrence.—Sucrose and invert sugar are found together in many commercial products, especially in raw sugars and molasses made from sugar cane, and in these products sucrose is usually predominant. They also form the principal saccharine contents of honey, the invert sugar, in this case, being the chief ingredient.
In commercial grape sugar, made from starch, dextrose is the important constituent, while in the hydrolysis of starch by a diastatic ferment, maltose is principally produced. In the manufacture of commercial glucose by the saccharification of starch with sulfuric acid, dextrin, maltose, and dextrose are the dominant products, while in the similar substance midzu ame, maltose and dextrose are chiefly found, and only a small quantity of dextrose.[194] In honeys derived from the exudations of coniferous trees are found also polarizing bodies not enumerated above and presumably of a pentose character.[195] In evaporated milks are usually found large quantities of sucrose in addition to the natural sugar therein contained. These mixtures of carbohydrates often present problems of great difficulty to the analyst, and the following paragraphs will be devoted to an elucidation of the best approved methods of solving them.
238. Sucrose and Invert Sugar.—The chemical methods of procedure to be followed in the case of a sample containing both sucrose and invert sugar have been given in sufficient detail in preceding paragraphs (124, 171). When, however, it is desirable to study further the composition of the mixture, important changes in the method are rendered imperative. While the estimation of the sucrose and the total invert sugar, or the sum of the dextrose and levulose, is easy of accomplishment the separate determination of the dextrose and levulose is not so readily secured. In the latter case the total quantity of the two sugars may be determined, and after the destruction or removal of one of them the other be estimated in the usual way; or in the mixture the levulose can be determined by the variation in its gyrodynat, caused by changes of temperature.
239. Optical Neutrality of Invert Sugar.—The gyrodynat of levulose decreases as the temperature rises (107) and at or near a temperature of 87°.2, it becomes equal to that of dextrose, and, therefore, pure invert sugar composed of equal molecules of levulose and dextrose is optically neutral to polarized light at that temperature. On this fact Chandler and Ricketts have based a method of analysis which excludes any interference in polarization due to invert sugar.[196] To secure the polarization at approximately a temperature of 87°, a water-bath is placed between the nicols of an ordinary polariscope in such a way as to hold a tubulated observation tube in the optical axis of the instrument. The ends of the bath, in the prolongation of this axis, are provided with clear glass disks. The space between the cover glasses of the observation tube and the glass disks of the bath is occupied by the water of the bath. When this is kept at a constant temperature it does not interfere with the reading. The observation tube may be of glass, but preferably is constructed of metal plated with platinum on the inside. For the most exact work the length of the observation tube, at 87°, is determined by measurement or calculation. The bath is heated with alcohol lamps or other convenient means. The arrangement of the apparatus is shown in Fig. 75.
In a mixture of sucrose and invert sugar any rotation of the plane of polarized light at 87° is due to the sucrose alone. In a mixture of dextrose and sucrose the polarization is determined, and, after inversion, again determined at 87°. The latter number is due to dextrose alone, and the difference between the two gives the rotation due to sucrose.