INDUSTRIAL A N D ENGINEERING CHEMISTR Y
November, 1924
USES OF DEXTROSE Dextrose is not intended to be used as a substitute for cane sugar, but owing to certain peculiarities which it possesses it is in certain respects superior to cane sugar for manufacturing purposes. One of these is its tendency to form microscopically small crystals. Thus, fondants, creams, etc., can be produced which have that velvety feel and appearance so desired in these products. It also seems to affect the crystallization of cane sugar in the same way, and has thus become a necessity to the manufacturers producing the more fancy types of candies, cakes, cold icings, milk chocolate, chewing gum, etc. It does not possess the sweetness of cane sugar and, according to some of the larger fruit packers, it is the ideal sugar for preserving fruits of mild or delicate flavors which are masked by the extreme sweetness of cane sugar when used in the amounts necessary. I n the baking trade it is preferred as the yeast nutrient in a bread sponge. For medicinal purposes, especially in cases of acidosis, anemia, and the earlier stages of Bright’s disease, it is the only sugar now commercially available which does not aggravate these conditions. The ice cream trade desires the sugar on account of its
1175
lack of sweetness, because the average ice cream user demands a certain body which is produced only by the use of sugar, and by using refined dextrose this body can be more successfully produced without making the ice cream too sweet. The cruller and doughnut manufacturers and pancake flour manufacturers prefer the use of refined dextrose due to its low caramelization temperatures and the fact that it gives doughnuts and pancakes that delightful brown without any burnt taste. The cracker and biscuit manufacturers are using it for purposes best known to themselves. The manufacturers of commercial pectin are quite large users of this product. The wine and vinegar manufacturers use it in the natural fermentation processes, as it carries with it a maximum fermentability with no troublesome secondary flavors which later have to be removed in vinegars and which would spoil wine as it is consumed direct. Dye manufacturers are becoming large users of the product. The condensed milk manufacturers are very desirous of using it. I t s preserving qualities are equal to those of cane sugar, and in this particular case its lack of sweetness is the desirable feature.
Adsorption Effects of Filtering Materials on Sugar Solutions’ By G . H.Hardin and F. W. Zerban NEWYORKSUGAR TRADE LABORATORY, NEW YORK,N. Y.
wholly reversed to negative N THE course of the Dry filter paper takes u p water from sugar solutions, while filter a d s o r p t i o n . Freundlich4 routine work performed paper with high moisture content tends to dilute the sugar solution; states that negative adsorpin this laboratory, it there is an intermediate point where equilibrium obtains. The tion is more often observed was ‘frequently observed effect of these phenomena on saccharimetric analysis has been in the case of gels than with that when a raw sugar solustudied quantitatioely, and it is concluded that in practical sugar other a d s o r b e n t s . T h e tion prepared for polarianalysis, using dry filter paper, it is not suficient to discard only a well-known occurrence of metric analysis was, for small part of the fiItrate, as practiced by some analysts, but that at “adsorption water” in beet some reason or other, passed least 25 of the 100 cc. should be rejected to attain the closest possible and cane fiber should also through a second filter, unapproximation to the correct polarization. Absorbent cotton acts be mentioned in this connec. . precautions of der the usual 1ih.efilter paper, while dry asbestos or Filter-Cel did not measurably tion. covering with a watch glass, affect the polarization. In view of these cmsiderthe polarization of the final ations a study was made of filtrate was always slightly but distinctly higher than when the analysis was repeated ac- the effect of the commonly used filtering materials, such as cording to the regular procedure with one filtration. This in- paper, cotton, asbestos, and kieselguhr, on the concentration of crease in polarization may, a priori, be ascribed either to evap- sugar solutions. Most of the tests were made with ordinary oration, or to a concentration change brought about by the filter paper, as this is the medium used in regular sugar analyfilter paper itself. The first of these causes did not seem prob- sis. It was, of course, necessary either to avoid evaporation able, since Rates and PhelpsZ have shown that “practically all altogether or to be able to correct for it. increase in polarization, regardless of atmospheric conditions, In some experiments made for the purpose of orientation may be prevented by covering the funnel with a watch glass,” an attempt was first made to attain this end by centrifuging even if the solution is filtered twice through the same filter. the mixture of paper and sugar solution in a conical glass According to previous literature, cellulose is, from the tube, filling the other tube with the sugar solution itself. colloid-chemical standpoint, a gel, and as such sorbs water Both tub& were covered with rubber caps. It was found quite strongly. References cited by Bancroft3 show that impossible to obtain a clear enough liquid from the mixture absorbent cotton takes up 21 per cent of water in the presence to be able to make accurate readings in the saccharimeter. of saturated water vapor, and that it will hold 400 per cent Filtering the mixture of paper and sugar solution through a of liquid water when centrifuged wet a t 4000 r. p. m. It is small piece of filter paper or a little asbestos placed over the therefore not surprising that, although filter paper in many end of a pipet with broken-off point was also tried. But here cases exhibits positive adsorption, this is often reduced in there is the objection that the solution is under a partial degree by the simultaneous sorption of water, and may be vacuum while being filtered. The average results by both of these methods gave an’in1 Presented before the Division of Sugar Chemistry at the 67th Meeting of the American Chemical Society, Washington, D. C., April 21 to 26, 1924. crease of 0.4’ V. when 100 cc. of a normal solution of refined
I
2
Intern Sugar J . , 16, 266 (1914).
3
“Applied Colloid Chemistry,” p. 76.
4
“Kapillarchemie.” 3rd ed., p. 046.
Vol. 16, No. 11
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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sugar were left in contact with three filter papers of 18 cm. diameter for a few minutes. As there mere serious objections to both of these methods, they were abandoned in favor of ordinary filtration through filter paper, but with the precautions already mentioned as indispensable. EXPERIMENTAL I n each one of the following series of tests a stock solution with a known concentration of refined sugar was prepared. The filter papers whose effect was to be measured were placed in small flasks. I n each of the flasks 100 cc. of the sugar solution were then added, and the flasks immediately stoppered. One flask, to be used as a blank, received only the sugar solution. After agitating and allowing to stand for a definite length of time, the solutions were filtered through filter papers of uniform, known moisture content, the funnels being covered immediately with watch glasses. The polarization of the filtrate of the blank solution was used as a basis of comparison. All the work was carried on in the constant temperature laboratory at a uniform temperature of 20' C. By this procedure the effect of the following factors was investigated, keeping the other conditions constant in each series: 1-The quantity of the paper, by using one, two, and three papers. 2-The quality of the paper, by using ( a ) a paper of domestic manufacture of about 18 cm. diameter and an average dry weight of 1.81 grams; (a) an imported paper of about same size, average weight 1.65 grams; (c) another imported paper, again about same size, average weight 1.68 grams. 3-The moisture content of the filter paper. This war: varied by using filters dried in the oven a t 100" C., others kept in a desiccator over calcium chloride, still others taken from regular stock, and also filters kept over water in a desiccator. The moisture in the filter papers used was determined in each case. 4-The concentration of the sugar solution, using normal, half normal, and quarter normal concentration. %The time 01 contact between filter paper and sugar solution.
I n all of these experiments the entire filtrate was collected, which took only very little time, as refined sugar was used. This in itself would cut the evaporation to a minimum. The
Fro. 1
polarizations were usually made by two observers on two different instruments, whose scale errors almost exactly counterbalance each other, and the averages taken. All other necessary precautions, such as use of the bichromate cell, etc., were also carefully observed. In a number of tests it was found that the time of contact beyond a certain point has no measurable effect, the same results being obtained after 45 minutes as after 2 minutes.
The results for all the other factors are given in the accompanying tables: CHANGES IN POLARIZATION Moisture in paper Per cent
0.00
0.00 0.00 1.00 4.65 11.16 0.00
AVERAGE CHANGES BASEDO N BLANK 1 Paper 2 Papers 3 Papers Normal solution, 26 grams per 100 cc.
+O. 15 +0.11
+O. 13
+0.25 t-0.20
....
Average for 1 paper
+O. 35 +O. 29
....
$0.23 4-0.12 -0.35 ' +0.12 4-0.37 0.00 +0.10 +0.27 +0.37 0.62 +0.09 1-0.20 +0.23 4.65 +0.10 +0.13 +0.15 5.90 $0.04 +0.10 +0.13 14.50 -0.12 -0.25 -0.35 0.00 4-0.17 +0.27 4-0.37 0.70 +O. 13 +0.25 f0.37 4.93 4-0, 03 +o. 10 +O. 13 5.53 +o.oo +0.10 +0.11 8.34 -0.04 -0.10 -0.15 Half normal solulion, 13 grams p e r 100 cc. 0.00 +o. 10 $0.13 +o. 20 4.91 +0.04 +0.07 +0.09 13.85 -0.02 -0.09 -0.17 0.00 +0.08 4-0.12 +0.17 5.90 +o, 00 +0.05 4-0.05 14.69 -0.02 -0.10 -0.17 0.00 +o. 10 +0.14 4-0.20 4.97 +o.oo +0.05 +0.09 13.86 -0.02 -0.10 -0.17 Quarter normal solulion, 6.5 gram8 per 100 cc. (As the differences found in this case were so slight as t o be i-0.07 +O. 04 -0.07
+0.13 +0.11 -0.12 -I-0.23
4-0.125 +0.10 +0.13
+O. 07 +O. 045, -0.085 4-0. 12 +0.12 +o, 09 +0.06 +0.045 -0.12 4-0.135 +o. 125 +0.04 4-0.035 -0.05 +0.07 4-0.03 -0.05 4-0.06 +o 02 -0.05 f0.07 $0.02 -0.05
difficult to determine, these tests were made only with oven-dried filter paper.) ,(a) 0.00 +0.02 +0.09 4-0.02 i-0.04 +0.04 $0.07 +o. 10 $0.05 0.00 +0.02 4-0.08 +0.02
The results obtained with the normal and half normal solutions are shown graphically in Figs. 1 and 2, in which the polarization changes are plotted vertically in degrees Ventzke, and the water content of the filter papers horizontally, in grams. DISCUSSION OF RESULTS
It is evident that of the different factors investigated, the weight of the paper, its moisture content, and the concentration of the solution have a profound influence on the polarization obtained. It is clearly seen that the polarization changes, up or down, increase numerically with the weight of the paper used. Perfectly dry paper gives a decided increase i n ' polarization, averaging about 0.12" V. per disk, whereas paper with 14.5 per cent moisture gives a decrease of 0.12' V., and midway between the two there is a point where the two effects balance each other. The polarization of a half normal solution is changed about half as much as that of a normal solution, and that of a quarter normal solution about one-fourth as much. The slight discrepancies in this respect are within the limits of error. Although the accuracy of the method used is quite sufficient to establish these facts, it is impossible to detect a difference to be ascribed to the quality of the paper. A decided difference in this respect could hardly be expected between filter papers that are made for one particular purpose. It is also impossible from the data found to determine the exact trend of the polarization-moisture curve, which appears to approximate a straight line, and to ascertain whether it satisfies the exponential adsorption formula. I n order to do this, more refined equipment, such as a highly sensitive refractometer, would be necessary. The information gained, however, is quite sufficient to establish the principle, and to furnish a basis for practical application in sugar analysis. This statement is confirmed by conclusions which may be drawn from the fact that the method used permits a double check, provided there is no adsorption of sucrose. I n the normal solution series, Paper ( a ) , the difference in water content between dry and 11.16 per cent moisture is 0.202
INDUXTRIAL AND ENGINEERING CHEiMISTRY
November, 1924
gram, and this caused a total change in polarization, which is also a direct measure of the water concentration, of 0.210" V. Similarly, for Paper ( b ) , we find 0.239 gram against 0.240"V. With the half normal solution series, Paper (a), the figures are 0.251 gram and 0.240" V. Some one might suggest that the increase in polarization of a sugar solution after contact with dry filter paper could also be ascribed to a possible solvent action of the sugar solution upon certain dextrorotatory components of the filter paper. But this is not the case, as was demonstrated by parallel experiments with a normal levulose solution, which showed an average increase in the levorotation of 0.09" V. per filter, and not a decrease. Dextrose solutions of normal concentration gave the same results as sucrose solutions, and it was also found that dextrose dissolved in hydrochloric acid of the concentration used in the Clerget inversion method suffers the same polarization changes as in pure aqueous solution. Testtl with 1, 2, and 3 grams of dry absorbent cotton gave an average increase in polarization of a normal cane sugar solution of 0.07" V. per gram. This is at the same rate as found per gram of filter paper. On the other hand, using I, 2, and 3 grams of dry asbestos or Filtrr-Cel, no measurable change could be detected in the polarization of a normal cane sugar solution. APPLICATION TO SUGAR ANALYSIS When a sugar solution is simply poured through a filter paper, the contact is not so intimate as when the paper is agitated with the solution. For instance, dipping three dry filter papers into 100 cc. of a normal solution of refined sugar gave an increase in polarization of only 0.04" V., or a little over 0.01" V. per paper. Simply passing the solution through a dry filter paper gave an increase of about 0.02" to 0.03" V. But if the rate of filtration was slowed down by placing a piece of' rubber tubing over the mouth of the funnel and adjusting a screw clamp in such a way that the solution drips through slowly, an increase as high as 0.11 V. per paper could be observed. Similar results were obtained by first closing the clamp entirely, and releasing the filtrate after
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turbid and must be rejected since they would prevent an accurate reading in the saccharimeter. Curiously enough, nearly all the authorities consulted by the writers state or imply in their directions for analysis that rejection of the first part of the filtrate is necessary for the sole reason that it is turbid. Only one of them mentions that "the first portions of the filtrate should be rejected, because they contain the moisture of the filter paper." It is now evident that this rejection is necessary not only on account of turbidity, but also because the dry paper prescribed by the International Commission for Uniform Methods of Sugar Analysis, and used by all careful analysts, increases the concentration of the filtrate and especially of the first runnings. I n the directions prescribed by the various authorities, the quantity of filtrate to be rejected varies from "a few drops'' through a few cubic centimeters to a substantial portion of the filtrate. In the light of the results described above it was necessary to investigate how much of the filtrate of a clarified raw sugar solution must actually be discarded to obtain a minimum reading which shows no further measurable change when still larger quantities of filtrate are rejected. A number of tests were first made with normal solutions of refined sugar which were filtered through a dry paper. The rate of filtration was slowed down by the devices described above. It was found that as the quantity of discarded portion increased the polarization of the remainder fell, and when 25 cc. or more were rejected the polarization of the remainder became constant and checked within the limits of error with the original solution. The same tests were then repeated with raw sugars. I n order to avoid errors caused by nonuniformity of sample, five times the normal weight of sugar was dissolved in water, clarified as usual, made up to 500 cc., and aliquots of 100 cc. each of the well-shaken suspension used in each test. The results were the same as with refined sugar. It is evident, therefore, that if dry filter paper is used, as prescribed by the International Commission, it is necessary to discard not only the first few drops of filtrate, but. to reject at least 25 cc. While under these conditions no further measurable decrease in polarization of the remainder could be observed, a slight plus error is probable, the cumulative effect of which may not be inconsiderable during a year's work. Theoretically, the best procedure would be to use filter paper of such moisture content as will have no effect on the concentration of a normal sugar solution, or to resort to filtering materials which have no effect on the concentration. In practice, however, both of these measures present considerable difficulties. This makes it all the more necessary to minimize the error shown to be present by discarding as much of the filtrate as will still leave a sufficient quantity of liquid for polarization. Intersectional Meeting at Cleveland
FIG.2
several minutes' standing. Cnder conditions such as these the time of contact becomes of importance, and this naturally has a bearing on the analysis of raw sugars where the filtration usually is slow. Fortunately, the entire filtrate is never used in the analysis of raw sugars, because the first portions of it are usually
A one-day intersectional meeting is t o be held at Cleveland, Ohio, on November 6, with active participation by all the sections in Ohio, Michigan, northern Indiana, and western Pennsylvania. L. H. Baekeland, C. L. Parsons, J. F. Norris, A. P. Mathews, H . H. Dow, Harry Fisher, W. G. France, N. E. Gordon, and others will appear on the program, and the general will be opened to discussion. policy of the SOCIETY The meetings, which will be from 10:30 A.M. to 9 P.M., will be held at the Hotel Winton, and the charge for lunch, dinner, and a small registration fee will be about $3.25. Cleveland is easily reached by rail and auto, so members of the sections named need take, at most, one day and two nights for the trip. Our national gatherings are so large that some of the decided advantages of smaller meetings have been lost. Here is an opportunity !
