Turbidity in Sugar Products 11. Effect of Independent Variation of Suspended and Coloring Matter on Transmittancy and Tyndall Beam Intensity F. W. ZERBAN, LOUISSATTLER, AND IRVING LORGE New York Sugar Trade Laboratory, Inc., 80 South St., New York, N. Y.
T
HE &-st paper of this Equations have been derived and graphs conship, but it contains eight constructedfor two systems containing both coloring stants and is too cumbersome series (8) dealt with the transmittancy and Tynmatter and turbidity, by means of which their t o use ranges limited i n p r athe c t isimpler c e . Within power dallbeam intensity of a raw sugar solution at varying depthof layer, concentration can be derived from measurements formula, which applies to the and a t varying concentration obof transmittancy and Tyndall beam intensity. optical density, affords in this tained by dilution with a clear, I n the two fairly closely related systemscase also close approximations to Filter-Cel plus caramel solution, and unfiltered the experimental data. colorless sugar sirup. The proportion between suspended plus filtered sugar sirups-the relationships matter and molecularly dispersed formulas Sauer (6) which hasare derived applicable certain to coloring matter remained always between and turbidity concentration On the suspensions in colorless media, one hand and transmittancy and Tyndall beam particularly for the Pulfrich the same. Under these circumstances the ratio between the intensity on the other have been found not to be photometer. According to him, identical. Consequently, a simpl$ed matheif the absorption is SO small as to Tyndall beam intensity and the transmittancyis,within s limited matical treatment of the problem of determining range, a power function of the be tensity negligible, is directly the proportional Tyndall into depth or of the concentration of turbidity and in the presence Of each Other the thickness. If the absorptotal light-absorbing mamust be confined to the Particular system which tion is considerable, it may be terial. is being studied, and specific relationships which corrected for by applying a factor hold for one case cannot be applied indiscrimibased on the optical density. The various products of the Sauer states that the absorpsugar house present a much nately to any other system. Photometric determore complicated problem, betion due to coloring matter in minations are cause here coloring matter and 't be preferred to true solution is usually slight in suspended matter vary in&mere comparisons with empirical standards. comparison to that caused by the suspended particles, and pendently of each other. Furthermore, the size and shape of that if the cell thickness is propthe suspended particles and their light-absorbing and reflect- erly chosen so that the absorption becomes negligible, the ing properties may vary not only from one product to observed Tyndall beam intensity will vary directly with another, but also for one and the same product through the total number of suspended particles. Even if the colorcoagulation or peptization produced by mechanical effectsor ing matter caused considerable absorption, it should be posby the mere time factor. sible, according to Sauer, to apply a correction factor. The Even if the characteristics of the particles and the possi- writers' experience has shown, however, that such a simple bilities of change in them be left out of consideration, no gen- procedure cannot be used in the case of systems like sugar era1 theory of the transmittancy and Tyndall beam intensity products, where the absorption due to coloring matter is of systems containing both suspended and coloring matter in very high and where multiple reflection is a further disturbvarying proportions has as yet been developed, previous work ing factor. having been confined principally to suspensions in colorless The wide gap existing between the systems which have remedia where absorption is due solely to the suspended matter. ceived mathematical treatment and those with which the C u m i n s and Badollet (2) have recently reported measure- writers have to deal required bridging. Experiments were ments of Tyndall beam intensities in sugar products and other therefore undertaken to measure the transmittancy and Tyncolored media; but while they imply that the presence of dall beam intensity of turbid, colored solutions of known comcoloring matter affects the readings obtained, they do not position, in order to ascertain the practical applicability of specify how the necessary corrections may be made. this method for the measurement of turbidity and of color. Formulas covering suspensions in colorless media, and assuming perfectly diffused light, have been established by SERIESA. BENTONITEAND CARAMEL In similar investigations Lindfors (4) and Balch (1) used Wells (7) on thre basis of the theory of Channon, Renwick, and Storr. Wells shows that in such systems the optical bentonite to produce turbidity, and caramel as the coloring density (- log T)is not directly proportional to the depth matter. The writers adopted these same materials in the or the concentration (Lambert-Beer law), but increases more first series of their experiments. Systems of this nature preslowly than either, because part of the incident light is lost by sent great difficulties in technic, because of their instability. reflection or scattering. The rigorous equations are rather After considerable preliminary work a sufficiently stable turinvolved, but for limited ranges, and well within the limits of bid medium was prepared by suspending bentonite in a soluexperimental error, the optical density increases linearly with tion of gum acacia, which acted as a protective colloid. a power function of the depth, the exponent being less than The coloring matter was prepared according to Ehr1ichjs unity. The Tyndall beam intensity is an even more complex method (3) from Domino tablet sugar, by heating the owdered function of the depth or concentration of suspensions in Color- substance in vacuo in an oil bath at 200' C. and holing it at less media. Wells gives a complete formula for that relation- that temperature for one hour after all frothing had ceased. 178
~
May 15, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
One hundred grams of the caramel thus obtained were ground to a fine powder and dissolved in 200 cc. of distilled water. The solution was treated with 5 grams of x-ray grade of barium
sulfate, shaken thoroughly with it, and filtered by suction through acid-washed asbestos on a Jena fritted glass funnel. The filtration was repeated ten times through the same ad, and the final filtrate was collected in a clean, dry filter flast. This caramel solution was found, on subsequent test, to be as free of suspended matter as freshly distilled water. To prepare the mixtures containing specified quantities of turbid and coloring matter, the stock bottles of bentonite suspension and caramel were vigorously shaken and placed in a water bath held at 20' C. When the contents had reached 20' C. the caramel solution was placed dropwise in a series of 25-ml. volumetric flasks, from a 5-cc. microburet with a ground tip. The desired amount of bentonite suspension was then added from a graduated pipet, the stock bottle being well shaken before each removal. The mixture of bentonite suspension and caramel solution was diluted with distilled water nearly t o the mark, and the volume finally adjusted at 20' C. The photometer readings were taken after less than 2 hours. The flasks were slowly rotated for mixing. Even this gentle treatment seriously affects the Tyndall intensity readings, and for this reason the transmittancies were determined first, as these are only slightly affected. Thorough mixing is essential for the Tyndall measurements, but the suspensions must not be agitated vigorously. The cells were rinsed four times with the solution in order to insure complete removal of previously contained material. The cover of the cell was put in place, and the cell carefully washed with distilled water, dried, and polished. Special care must be taken to insure optically perfect cell walls.
Standardization of technic was found to be of paramount importance. Equal timing of similar operations, uniform rate of mixing, and the most scrupulous maintenance of comparable experimental conditions are mandatory if any significance is to be attached to any of the observed readings. Thirty-five different mixtures of suspended and coloring matter were prepared, the bentonite concentration being varied in five steps and the caramel concentration for each of these suspensions in seven steps. The transmittancy and Tyndall beam intensity of all the mixtures were determined with the Pulfrich photometer (8) in a 5.09-mm. cell, under the green and red filters-that is, a t effective wave lengths of 529 and 621 mp, respectively. On the basis of these measurements the mathematical relationships between the transmittancy and the Tyndall beam intensity on the one hand, and the concentration of coloring matter and turbidity on the other, were formulated, and the constants in the formulas evaluated for a number of typical cases. The results proved that the particular kind of bentonite used had an adsorptive effect on the caramel, and that for this reason the concentrations of suspended and coloring matter in the mixtures on which the observations were made, were different from those before mixing. Although the findings are of considerable interest from the standpoint of adsorption equilibria, they do not furnish a solution of the present problem, and the results are therefore omitted here. It is evident that when Lindfors' method of preparing bentonite-caramel standards is used, it must first be ascertained whether or not the particular bentonite adsorbs caramel; if it does, the standards will be valueless.
SERIES B. FILTER-CELAND CARAMEL Experiments were next undertaken with Filter-Cel purified by acid washing and fractional sedimentation. The FilterCel suspension and caramel solution were prepared in the same manner as the corresponding materials in Series A. The transmittancies and Tyndall beam intensities of these mixtures were measured as described above, with the results -shown in Tables I and 11. The relations between the transmittancy and Tyndall beam intensity on the one hand, and the concentration of turbidity and coloring matter on the other were now analyzed separately. The following symbols are used in this discussion :
179
N = cc. of bentonite suspension (Concentrationof turbidity) C = drops of caramel solution (concentration of coloring matter) T = per cent transmittancy D = optical density (-log T ) R = Tyndall beam intensity, in per cent of standard block' TABLEI. TRANSMITTANCIES OF FILTER-CEL-CARAMEL MIXTURES DROPSOF
-
CARAMEL 0 cc.
4 cc.
FILTER-CEL SUSPENSION 8 cc.
RED FILTFIR,
0 4 8 12 16 20
100.00 99.02 90.90 89.58 81.82 76.68
98.42 88.28 84.62 79.20 74.56 73.28
0
100.00 87.62 72.68 63.28 52.17 42.92
91.80 77.42 65.96 54.88 44.51 40.58
82.18 81.78 77.96 75.02 70.64 66.76
12 cc.
&MI-MM.
16 cc.
80.58 76.80 71.96 67.39 64.26 58.73
76.39 68.18 67.14 63.99 60.91 58.06
QREEN FILTER, 6.m-MM.
4 8 12 16 20
78.21 68.31 58.95 49.47 42.78 36.16
20 cc.
24
72.70 65.72 64.58 61.07 57.11 54.18
65.14 63.36 59.75 57.95 54.79 50.75
65.58 52.91 46.52 39.37 33.19 28.75
58.60 51.10 43.28 36.90 31.38 25.54
OC.
CELL
CELL
75.04 62.87 53.24 45.73 39.29 30.86
69.95 55.62 49.82 42.49 35.57 29.92
TABLE 11. TYNDALLINTENSITIES OF FILTER-CELCARAMEL MIXTURES DROPS of CARAMEL 0
CC.
FILTER-CEL SUSPENSION
4 cc.
8
12 cc.
CC.
R E D FILTER, 6.08-MM.
0 4 8 12 16 20
50 114 103 136 200 122
1462 1387 1256 1295 1217 989
0 4
18 36 26 32 36 24
465 413 305 264 188 155
3254 3098 2842 2427 2341 2185
QREEN
8
12 16 20
16 cc.
20 cc.
24 cc.
5338 6022 5692 5492 4538 3923
7118 6379 5972 5933 5476 5568
1947 1701 1437 1182 950 517
2302 1877 1478 1284 1060 1065
CELL
4190 4140 3862 3698 3190 3069
4979 5267 4807 4639 4489 4354
FILTER, ~ . o ~ - M MCELL .
1123 962 751 502 438 361
1513 1284 1030 842 530 448
1792 1562 1262 1131 913 779
TRANSMITTANCY. An examination of the transmittancy figures showed that when turbidity is constant and coloring matter varies, the optical density is directly proportional to the color concentration-i. e., that Beer's law holds for the coloring matter, irrespective of the turbidity present simultaneously. Expressed in a formula, -log T
=
c C, or C =
-log T -
Under the red filter c = 0,00590, and under the green filter 0.018075. Balch had previously found that Beer's law does not apply for varying turbidity a t constant color, and the writers pointed out (8) that Balch's results satisfy a power formula. This has been confirmed in the present series of experiments. The formula is as follows:
N
=
kDn, or D =
($
For the particular system investigated the numerical value of the constants is: n
log IC
RED FILTER 1.188 2.24645
GREEN FILTER 1.232 2.17266
1 The absolute Tyndall beam intensity of standard block 323, used b y the writers, is reported by Zeiss to equal 0.00282 of the intensity of the incident light, for the green screen, under the experimental conditions of the Pulfrich photometer. Corresponding figures for the blue and red screens have not been furnished. T o calculate the absolute Tyndall beam intensity of a solution, 0.01 R is multiplied by the absolute intensity of the standard block for the same screen, and the product multiplied b y a factor which varies with the vessel used as the container for the solution. For a 2.5-mm. plane parallel cell this factor is 6.5.
ANALYTICAL EDITION
180
The absorptions due to the coloring matter and to the turbidity are additive, and the combined formula may therefore be written -log T = cc
+ (;
jz
(3)
The equation for R, as a function of written
R = b d-C log N
VALUEE
c
-
0
4
0 4 8 12 16 20
100.0 94.7 89.7 85.0 80.5 76.2
90.9 86.1 81.6 77.2 73.2 69.3
0 4 8 12
100.0 84.7 71.7 60.7 51.4 43.5
88.5 74.9 63.4 63.7 45.5 38.5
OF
VALUESOF N 8 12
FOR
20
24
73.7 69.8 66.1 62.6 59.3 56.1
69.2 65.5 62.1 58.8 55.7 52.7
65.1 61.6 58.4 55.3 52.4 49.6
68.6 58.1 49.2 41.6 35.3 29.8
63.7 53.9 45.6 38.6 32.7 27.7
59.2 50.2 42.5 36.0 30.4 25.8
R E D FILTER
84.3 79.9 75.6 71.6 67.9 64.3
78.7 74.5 70.6 66.8 63.3 60.0
QREEN FILTER ~~
20 l6
80.7 68.3 57.8 49.0 41.5 35.1
74.2 62.8 53.2 45.0 38.1 32.3
COLOR
GREENFILTER k 725 1880 573 1488 1178 453 932 358 283 738 a
4 8 12 16 20
REDFILTER (I
6189 5649 5156 4706 4295
IC 2291 2101 1926 1766 1619
Both a and k are functions of the color concentration C:
a = bd-0 b = cf-C,or log a = log b (log d ) C logk = log e (logf) C
-
(5)
REDFILTER 3.83130 0.009915 3.39673 0.009175
3.37569 0.025382 2.96248 0.025535
The values of a and k cannot be extrapolated to zero color. With no coloring matter present, the values of log a and log k are GREENFILTER 3.33786 2.92840
log a log k
RED FILTER 3.79302 3.37566
If the values of a and k shown above are substituted in formula 4, the figures given in Table IV are obtained. TABLEIV. CALCULATED VALUES OF R, O F c AND N VALUES
Considering the experimental difficulties and possibilities of shifts in the colloid equilibrium during observations, the agreement between found and calculated values is good for the green filter. For the red filter the figures do not check so well, owing to the disturbing differences in tint in the two halves of the field. The results show that no adsorption of caramel by the Filter-Cel took place, because in every case the ratio between the transmittancy of the turbid colored solution and that of the corresponding colored solution free from turbidity was the same as the ratio between the transmittancy of the turbid colorless solution and that of water. This is the rule which Balch ( I ) had previously found to hold when there is no adsorption. TYNDALL BEAMINTENSITY. An examination of Table I1 shows that the Tyndall beam intensity increases with the turbidity at each color concentration. With the turbidity constant and color varying, irregular figures are obtained a t turbidity 0, due to small and unavoidable admixture of turbidity. At turbidities above 4, increasing color generally causes a decrease in the Tyndall intensity. As in the bentonite-caramel series, where the intensity first increased and then decreased, a few of the figures in Table 11, between colors 0 and 4 under the red filter, show a tendency to rise, but above color 4 the maximum of the curve has evidently been passed. Between the limits of turbidity from 4 up to 24 and of color from 4 up to 20, the Tyndall beam intensity is, at constant color concentration, an approximately linear function of the log of the turbidity Concentration, according to the formula R =alogN-Ic (4) The values of the constants a and k were found to be
- ef-0
GREENFILTER log b log d log e log f
STATED VALUES
16
C and N , may thus be
The numerical values for log b, log d, log e, and log f in this particular system are
When the values for C, N , c, k, and ~t are substituted in this formula, the transmittancies given in Table I11 are obtained. TABLE111. CALCULATED VALUES OF T OF c AND N
Vol. 6 , No. 3
OF
c
4
8
FOR
VALUESOF N 12 16
STATED VALUES 20
24
1773 1539 1219 965 765 606
1980 1721 1363 1079 853 677
2157 1870 1481 1173 929 736
5101 5161 4701 4280 3900 3553
5703 5761 5248 4782 4356 3969
6195 6251 5696 5190 4729 4309
QREIEN FILTER
0 4 8 12 16 20
463 407 323 256 203 161
Ill8 973 771 611 484 383
0 4 8 12 16 20
1363 1435 1300 1178 1067 967
3232 3298 3001 2730 2484 2260
1501 1314 1033 818 648 513 RED FILTER
4326 4388 3995 3638 3313 3016
Under the green filter, the agreement between calculated and found values is satisfactory, except where the experimental values are obviously out of line as shown by a direct comparison of found values with those adjacent in different directions. Under the red filter, the agreement is not nearly as good as under the green, for the same reason as given in the discussion of the transmittancy figures. In both spectral regions the agreement is less good a t high turbidity and high color. Here multiple reflection appears to become more pronounced, and this is probably one reason for the observed deviations. By means of formulas 3 and 5 above, C and N in unknown mixtures of the caramel and Filter-Cel used in this series may be calculated after T and R have been determined, but the result may be ascertained more quickly and easily by means of a graph. SERIESC. MIXTURES OF SUGAR SIRUPS The next step in .this investigation was to ascertain whether the relationships found for the Filter-Cel and caramel mixtures would also hold in the case of actual sugar products. This problem was attacked by selecting a very dark raw sugar containing a large quantity of suspended matter, dissolving it to a sirup of 60" Brix and removing coarse suspended matter by vacuum filtration through 250-mesh bronze gauze. Part of this sirup was carefully filtered through purified Filter-Cel and asbestos to free it as far as possible of suspended matter. A white sugar sirup was prepared from Domino sugar tablete, decolorized with Suohar, and filtered like the raw sugar sirup. All three sirups were finally adjusted again to 60' Brix by re-, fractometer. Solutions containing varying proportions of coloring matter and turbidity were then made by weighing and mixing the three sirups in proportions of 0 to 5 parts of each.
If one part of unfiltered raw sugar sirup represents one unit of coloring matter (C) and one unit of turbidity ( N ) , then
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 15, 1934
one part of filtered raw sugar sirup equals one unit of coloring matter plus a small amount of residual turbidity not removed by filtration, and one part of filtered white sirup represents zero color plus a small amount of residual turbidity. The transmittancy and Tyndall beam intensity of all the mixtures were determined under three color screens, blue (449 mp), green (529 mp), and red (621 mp), in a 2.5-mm. cell. The results of these measurements are shown in Table V, where U indicates one part of unfiltered raw sugar sirup, F one part of filtered raw sugar sirup, and W one part of filtered white sirup.
181
centration, a value for W , known to be small, had to be assumed as a first approximation. Two sets of equations were therefore set up, in one of which the turbidity in W was assumed to be zero, and in the other equivalent to one-third of that in F. The results of these two sets of equations showed that within these limits the value for W had little effect on the values of R corresponding to U and of F , which came out very nearly the same.
From these data formula 6 was derived, and this made it possible to calculate the values of R corresponding to 1 W at color concentrations 1, 2, 3, and 4, from that found experimentally at zero color concentration. With R for 1 W known, the R values of U and F a t each color concentration could now be readjusted, and the final results of the calculaTABLE V. TRANSMITTANCIES AND TYNDALL BEAMINTENSITIES OF SIRUP MIXTURES tions are shown in Table VI. MIXTURES 6 C units 5 U , OF, O W 4 u , lF, O W 3u, 2F, O W
3F, UW 4F, O W OU, 5F, O W 4-C.iinits 4 U , OF, 1 W 3 U , 1 F, 1 W 2 U , 2 F, 1 W 1 U , 3 F, 1 W O U, 4F, 1W 3 C units 3 U , 0 F, 2 W 2 U , 1 F, 2 W 1 U. 2 F, 2 W O U , 3F, 2 W 2 C unibs 2 U, 0 F, 3 W 3W 1 U, 1 F 0 U, 2 F: 3 W 1 C unit 1 U, 0 F, 4 W 0 U , 1F , 4 W 0 C unit 0 U, 0 F, 5 W 2u, lU,
TRANSYITTANCY
Blue 2.15 3.27 4.23 5.97 7.87 10.37
Green 11.40 13.97 17.17 22.17 26.87 35.22
Red 29.25 33.53 40.50 46.35 54.25 66.27
4.77 5.93 8.18 11.93 16.00
17.10 21.40 26.37 33.08 43.30
36.70 42.92 50.73 60.47 72.37
9.80 13.33 17.70 24.45 21.07 27.43 40.23
26.42 33.92 42.07 53.17 42.33 49.03 64.87
47.30 55.30 65.28 77.85 60.62 71.93 83.05
44.90 62.03
64.35 80.50
78.45 ,90.62
100.00
100.00
100.00
BEAM TYNDALL
Blue 59.34 52.38 35.95 29.15 19.04 5.67
Green 913.3 799.1 492.9 367.8 194.5 51.24
75.12 898.5 59.12 600.8 44.72 441.2 30.03 274.4 60.51 7.32 106.7 81.2 51.4 12.9
917.1 592.9 330.9 90.3
863.8 128.9 74.13 396.8 10.91 55.08 121.4 480.8 14.03 54.15 6.83
21.55
INTEN3ITT
Red 5914 5117 3765 2376 1345 260.4
TABLE VI.
1211 40.6 0
19.05 2.60 0.14
213.9 13.64 1.68
1265 70.4 10.7
U
36.57 5.45 0.25
298.0 23.8 2.13
1446 135 11.64
U
65.1 6.15 0.43
421.4 17.0 2.69
1672 81.7 12.64
121.3 10.95 0.77
467.0 40.5 3.41
1682 105.7 13.74
1.37
4.31
14.92
W 3 C units F W 2 C units
F
W
REID
1 C unit
U
F
W
1737 160.7
In order to test this hypothesis of linear relationship between R and N , the values of R corresponding to one unit each of U, F , and W were calculated by the method of least squares from the experimental data given in Table V. In the series with 5 color units there are 6 equations, with two unknowns; in the series with 4, 3, and 2 color units there are 5, 4, and 3 equations, respectively, with three unknowns, but since the quantity of filtered white sirup was constant at each individual color con-
183.2 4.7 0
F
3340 1641 208.5
creases -log T by a constant amount, within the limits of error, and that the same is true €or each unit of F-W a t constant U. I n other words, Beer’s law appears to hold for both color and turbidity. The -log T increment for U-W is due to 1 C plus 1 N minus the residual turbidity in the filtered white sirup, while that for F-W represents 1 C plus the reBidual turbidity in the filtered raw sugar sirup minus the residual turbidity in the filtered white sirup. I n order to find the transmittancies for 1 C and 1 N,it is necessary to apply corrections for the residual turbidity in both filtered sirups. These corrections cannot be found from the transmittancy figures, because in the filtered raw sugar sirup the absorption effect of suspended and of coloring matter cannot be separately determined by this means, and bechuse the white sugar sirup showed zero turbidity by the transmittancy method although the Tyndall beam method revealed measurable turbidity. Therefore the necessary corrections had to be derived from the Tyndall beam intensities. TYNDALL BEAMINTENSITY. A glance a t Table V shows that a t constant color concentration there is an approximately linear relationship between parts of turbid sirup ( U = N ) and the Tyndall beam intensity under the green and red screens, but this relationship is obscured by the effect of the residual turbidity in the other two sirups, and more so under the blue screen.
11.94 1.75 0
4 C units U
210.1
A preliminary examination of the transmittancy figures in Table V showed that a t constant F each unit of U-W in-
GREEIN
W
4187 3259 1708 333.8
74.61
BLUE
6 C units U F
4925 3961 2816 1444
w
VALUESOF R, FOR ONE UNIT O F U,F, AND
0 C unit W
Simple addition of the R values for U ,F, and W shown in Table VI results in the R figures given in Table VII, representing the adjusted values of the Tyndall beam intensities for the sirup mixtures. The corresponding values of N are also presented, calculated by dividing the R values for the mixtures by the corresponding R values for 1 U (equivalent to 1 N),as given in Table VI. TYNDALL BEAMINTENSITY AND TURTABLEVII. ADJUSTED CONCENTRATION VALUESOF MIXTURESLISTED IN TABLEV
BIDITY
MIXTURES 5 C units 5U OF OW 4U 1F OW 3 U + 2 P + OW 2U 3F OW 1U 4F OW OU 5F OW 4 C units
++ + + + ++ +++ 4U + OF + 1W 3 U + l F + 1W 2 U + 2 F + 1W 1U + 3F + 1W O U f 4 F + 1W
3 C units 4-OF 2W 4- 1F 4- 2W 2F 2W OU + 3 F + 2W 2 C units 2U O F 4- 3W 1U 1F 3W OU 2F 3W 1 C unit 1U OF + 4 W OU+ 1 F C 4 W 0 C unit 3U 2U 1U
+ + +
++ + + + +
OU
+ OF + 5W
TYNDALL BWAM INTENSITY (E)
TURBIDITY CONCENTRATION (N)
Blue 59.7 49.5 39.3 29.2 18.9 8.8
Green 916 738 559 381 202 23.5
Red 6055 4885 3714 2544 1374 203
Blue 5.000 4.147 3.293 2.440 1.586 0.733
Green 5.000 4.026 3.051 2.077 1.103 0.128
Red 5.000 4.034 3.067 2.101 1.134 0.168
76.3 59.9 43.4 27.0 10.5
857 657 457 257 69.9
5071 3876 2692 1487 293
4.007 3.144 2.280 1.417 0.553
4.008 3.071 2.133 1.196 0,258
4.009 3.065 2.120 1.176 0.232
110.2 79.1 48.0 16.9
898 624 350 75.7
4350 3039 1728 417
3.013 2.163 1.312 0.461
3.013 2.094 1.174 0.254
3.016 2.109 1.203 0.298
131.5 72.6 13.6
851 447 42.1
3382 1692 201
2.020 1.114 0.209
2.019 1.060
0.100
2.023 1.072 0.120
124.4 14.1
481 54.1
1737 161
1.026 0.128
1.029 0.116
1.033 0.096
0.033
0.036
0.040
6.85
21.6
74.6
A comparison of the R values given in Table VI1 with those found experimentally (Table V) shows that the assumed linear relationship between N a n d R, a t constant color concentration, actually holds. The deviations are partly due to experimental error, because it is very difficult to prepare
ANALYTICAL EDITION
182
Vol. 6, No. 3
TRANSMITTANCY. The corrections for the residual turbidity in the two filtered sirups, shown in Tables VI and VII, were now applied to the transmittancies also, and it was found that Beer’s law holds for the range studied experimentally and well within the limits of errorPor both color and turbidity. The relationship may be expressed by the formula -log T = mN nC (7)
+
The values of the constants vz and n are BLUR 0.15510 0.17718
m n
GREEN 0 10408 0 08669
RED 0.07461 0.03416
Upon substituting these values and those for C and N in formula 7 , the transmittancies shown in Table VI11 are obtained. These agree satisfactorily with experimental values shown in Table V. Since Beer’s law holds for the transmittancies in respect to both C and N , these may be expressed directly in terms of -log T, as previously proposed by Balch: -1ogT
=
C + N
(8)
In this case the constants in formula 6 assume the following values:
log R
log log
Q
k
BLUE 3.13056 1 42545
GREEN 3.77551 1.23280
RED 4.40566 1.16568
FIGURE 1. NEGATIVE LOGOF TRANSMITTANCY A N D LOGOF TYNDALL BEAM INTENSITY, CORRESPONDIKG TO VARYINGCONCENTRATIONS OF COLORING C and N may then be calculated from MATTERAND TURBIDITY EXPRESSED AS NEGATIVE LOGSOB TRANSMITTANCY formulas 6 and 8:
homogeneous mixtures of these heavy sirups. Another reason is that the suspended particles remaining after filtration are probably different in size from those filtered out. The error due to this cause is smaller the more efficient the filtration. The relationship between R and N may be written R
=
bN
where b is a constant. The effect of the coloring matter on the Tyndall beam intensity may also be ascertained from Table VI. At constant turbidity the Tyndall beam intensity increases as the color decreases. When the logs of R for U = 1, N = 1 are plotted against C, a straight line is obtained. This relationship is expressed by
where k is a constant. Combination of the two formulas above gives
log a log k
BLUE 2.32117 0.26256
GREEN 2.79288 0.10687
Upon substituting these constants and the known values of C and N in formula 6, the data presented In Table VI11 are obtained. These show good agreement with the experimental values of Table VI1 in most cases.
+ (-
log T)
+
TYNDALL BEAMINTENSITIES AND TABLEVIII. CALCULATED TRANSMITTENCIES OF MIXTURESLISTEDIN TABLE VI1 hfIXTURBS
h nnita _ i _? _ .
5 4 3 2
U, U,
U,
U,
.
1U
OU.
RED 3.27836 0.03982
log u log k
The values of N corresponding to those of N log N/log k must be found from specially prepared tables or graphs, and C is then found from formula 8. Or the entire solution may be found from a graph, as shown in Figure 1.
3
(6)
This formula is similar to the one found previously for the Filter-Gel-caramel series, but it is simpler because within the range investigated R is proportional to N itself, not to log N . The values of the logs of the constants a and k in the above formula are
N + -log = -N- - log R log k log k
whence
0 U, 4 4 U, 3 U, 2 U, 1 U,
b = ak-c
R = uN1c-C
log R = logs +log N - ( - log T - N ) log k
1
2U , ‘12
U,
0 0 0 0 0
W W
0 F, lF, W 2 F, W 3 F, W 4F, 5 F, 0 W C units 0 F, 1 W 1 F, 1 W 2 F, 1 W 3 F, 1 W 4F, 1 W C units OF, 2 W 1 F, 2 W 2 F, 2 w
:zits2 F,
3
w
;2 $: 3” $ 1 C unit 1 U, O F , 4 W 0 U, 1 F, 4 W 0
0 U,
TYNDALL BEAMINTENSITIE6 Blue Green Red 67.19 906.8 6001 4842 47.44 730.1 37.67 553.3 3681 2522 27.91 376.7 1361 18.14 200.0 8.38 23.21 201.6 81.99 64.33 46.65 28.99 11.32
893.9 621.2 348.3 75.4
4348 3041 1734 427
766.1 4g;:i4
3197 ;1 ::
117.4 14.99
499.4 56.29
1789 166 3
6.91
22.34
110.3 79.17 48.02 16.87 132.3
:::::
c UUlt
OF, 5 W
5274 929.7 4020 712.3 2787 495.4 1546 278.1 305.2 59.84
75.93
TRANSMITTANCY
Blue 2.18 2.96 4.01 5.44 7.35 10.01
Green 11.12 14.04 17.74 22.41 28.30 35.75
Red 28.69 33.76 39.86 47.04 56.54 65.66
4.68 6.36 8.66 11.59 16.05
17.22 21.56 26.97 33.76 42.31
36.66 43.19 50.73 59.66 70.15
10.03 13.68 18.41 24.94
26.69 33.27 41.47 61’70
47.04 54.99 64.23 76’06
21.60
41.35
46.10 63.53
64.00 79.66
77.40 90.92
98.83
99.14
99.32
;:2;
80.36
gi:yf
The -log 2”s may finally be converted into -log t’s by reducing them t o the basis of 1 gram of dry substance in 1 CC. of solution and 1 em. thickness.
May 15, 1934
I 1v D U S T R I A L A N D E N G I N E E R I
Further research will have to show whether or not the relationships found for the particular raw sugar used in this investigation are applicable to color and turbidity determinations in other raw sugars. It is already known that the nature of the coloring matter varies from case to case, and this may be expected to be true for the turbidity also, especially as to particle size. Teorell (6) has found that the particle size of suspensions in colorless media may be determined by measuring either transmittancy or Tyndall beam intensity at several wave lengths, and it is possible that this observation may help to solve the present problem. Complete measurements with three color screens on about sixty different raw sugars have already been made, and turbidity has been determined in the same sugars by Balch’s method. The data are being correlated in two different ways: First, the color and turbidity of each sugar are calculated by formu-
IV G C H E M I S T R Y
183
las 6 and 8, and correlation is attempted on the basis of Teorell’s observations. The second method consists in a statistical analysis of the data, with the results by Balch’s method as the criteria. LITERATURE CITED (1) Balch, IND. ENQ.CHEX,Anal. Ed., 3, 124 (1931). (2) Cummins and Badollet, Zbid., 5,328 (1933). (3) Ehrlioh, F., 2. Ver. deut. Zuckerind., 59, 746 (1909). (4) Lindfors, IXD. ENG.CHEM.,17, 1155 (1925). (5) Sauer, private communication. (6) Teorell, Kolloid-Z., 53,322 (1930); 54, 58, 159 (1931). (7) Wells, Chem. Rev., 3, 331 (1927). (8) Zerban and Sattler, IND. ENG.CHEM.,A4nal.Ed., 3, 326 (1931). RBIC~IVIOD November 11. 1933. Presented before the Division of Sugar Chemistry a t the 86th Meeting of the Smerioan Chemical Society, Chioago, Ill., September 10 t o 15, 1933.
errriination of Viscosity of Dilute Solutions of Cassava Flour and Other Starches GORDON G. PIERSON,720 West Main St., Lansdale, Pa.
F
able to agree on t h e r e l a t i v e ROM the standpoint of ilfter describing certain viscosity characteristics of of the known and viscosities shown by a number of l a b o r a t o r y t e s t i n g the sa m p 1e s unless the differences v i s c o s i t y of s t a r c h i s used brands of cassava flour and other starches, ere pronounced, probably its most i m p o r t a n t carious methods Of festing are disclLssed and a $ u b s t a n t i a 1 benefit should va r i a b 1e characteristic. Cernew method and apparatus f o r preparing and result to all if the general printainly this is true among starches ciples a n d d i f f i c u l t i e s i n of the same kind. When starch testing dilute hot solutions are offeeredasstandard volved in viscosity determinasolutions having the same confor a large portion of the trade. tion were more clearly undercentration show the same risstood. cosity, they will also with few exIn spite of general misapprehension regarding the starch ceptions have the same adhesive or sizing value. Furthermore, among starches of the same kind, uniformity with re- viscosity test, it is becoming more generally realized that when spect to viscosity frequently means uniformity with respect all the conditions are known and properly controlled and the to other seemingly unrelated characteristics. Color, clarity, results properly interpreted, the values so obtained are as cleanness, resistance to fermentation, and fiber content can significant and as easy to duplicate as the average physical be suitably determined in the laboratory, but in general these or chemical test used for industrial control. characteristics have substantially less significance than viscosity. Broadly speaking, viscosity is the property which VlSCOSITY O F CASSAVA FLOUR most largely distinguishes the various grades in any one kind of colloidal material. The direct determination of strength The two great uses of cassava flour by industry are for glue, or sizing value on a laboratory scale is so compIicated and dif- which usually requires a cold concentrated alkaline solution, ficult as frequently to give highly erroneous indications, even and for sizing, which usually requires a hot dilute neutral in the hands of experts. solution. Terms commonly used in the trade to describe the conThis paper is principally concerned with the testing of dilute sistency of gelatinized starch solutions are viscosity, body, solutions of untreated cassava flour. The testing of concenfluidity, plasticity, paste strength, and jelly strength. Vis- trated alkaline solutions requires different methods and concosity, as it is commonly understood, has a meaning suffi- ditions and should be considered as a separate field. Freciently correct and descriptive for all practical purposes when quently a starch having a relatively high viscosity in concenhot dilute solutions are referred to, and will be generally used trated solution will show a relatively low viscosity in dilute in this article. solution. Even among dilute solutions, concentrations canThe testing of starch for viscosity has been considered a not be changed substantially without the possibility of bringrather hopeless proposition. Although a number of en- ing about a drastic shift in their relative viscosities. The results recorded in Tables I and I1 were all obtained in lightening articles (1, 2, 5, 6 ) have recently appeared, there is still much misunderstanding and lack of agreement on the a like manner by using the methods and apparatus described subject. Each laboratory has had an individual and usually below. The “Parts of Water” shown in these tables is the somemThat original method for testing, by which the results ratio of water to one part of starch or flour (containing 12 per were reported in some arbitrary unit. This difficulty, how- cent moisture), which was present a t the time the first test was ever, has been well recognized and has caused little confusion. made. The data presented shorn that the viscosity of colloidal The real difficulties hindering the proper appreciation and solutions produced by gelatinizing starch in water is largely common understanding of viscosity determinations have been dependent upon the conditions surrounding the preparation far more obscure. Experienced laboratories have rarely been of the solutions.
