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on sugar solids), moisture-free basis, each weighed portion being placed in a scoop or trough made by bending a 3- by 4-inch sheet of thin aluminum or brass. It may be necessary to vary the quantities of carbon from those given, depending upon the color of the solution and the decolorizing ability of the carbon. A weighed portion of the carbon is transferred to each flask, which is shaken continuously in the heating bath for 15 minutes. The carbon is best removed by filtration on an asbestos pad, using a Jena No. 1 filter. For paper filtration, approximately 1 g of kieselguhr is mixed with the contents of each flask, which is filtered by suction through a double layer of Whatman No. 42 paper, 7.5 cm in diameter, in a Büchner funnel. A battery of four filters with clean, dry receivers may be arranged and an extra receiver used for starting the filtration of each solution, in turn. When the filtrate becomes perfectly clear, the filter is placed in its receiver and the filtration completed. The decolorized solutions are cooled and thoroughly mixed, the refractometer Brix of each is determined, and the solutions, including the original undecolorized liquor, are evaluated photometrically, preferably at 560 mμ, the thickness, b, of the light-absorbing layer being governed by the color of the solution. From the Brix, layer thickness, and photometer readings (giving c, b, and T for each solution), log t is calculated as already described. These values of log t, without conversion to color units, are used for computing the values for plotting the isotherm.

Table 40 illustrates the manner of computing the isotherm data. The values of Care found by (-log t decol./-log t orig.) X100 to give a whole number and r= =100-C. The values of m as given may be called the percentage of carbon on saccharine dry substance.

TABLE 40.--Computation of data for the isotherm in figures 78 and 79

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The values of log r/m may now be plotted against log Cas rectangular coordinates, or as recommended by Sanders [45], r/m and Care plotted on double logarithmic paper, as shown in figure 79, the data being those of table 40.

Diluted molasses is preferred by many as a material for the decolorization test, since the solutions are easily filtered without suction. Diluted molasses is unstable in color, and stock solutions should therefore be prepared at least daily. This stock solution should not be too dark for ease of color determination or so light that it is too easily decolorized.

The procedure as outlined by Sanders [44] is as follows: Equal volumes (150 ml) of the molasses are pipetted into five 250-ml Erlenmeyer flasks. These are placed in a water bath and heated to 90° C. On each of five strips of white glazed paper 1 g of Filter-Cel is placed. Four portions of carbon are weighed, using, for instance, 0.1, 0.2,

0.4, and 0.7 g weighed to the nearest mg, allowance being made for the moisture content of the carbon. Each weight of carbon is placed on the Filter-Cel on each of the strips. The Filter-Cel alone is added to one of the flasks and the mixture of Filter-Cel and carbon to the other four. The heating is continued during 10 minutes after the addition, the flasks being shaken continuously. The flasks are removed from the bath and their contents filtered through paper on separate 60° funnels. Cloudy first-runnings are discarded or returned to the filter, only brilliantly clean filtrates being accepted for colorimetry. After cooling, the filtrates are measured photometrically, preferably at wave length 560 mp. Concentration of dry substance is not taken into account in this procedure. Thicknesses

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FIGURE 78. Adsorption isotherms of three decolorizing carbons. C Concentration of coloring matter remaining in solution plotted against r/m, where x is the amount of coloring matter removed by m grams of carbon.

(d) are reduced to 1 cm by dividing-log T as found or calculated from the photometer reading, by the length in centimeters of the cell used. If Meade-Harris color units are used, the number of units found, corresponding to the photometer scale reading, are divided by the cell thickness in centimeters.

Depending upon the system used, either-log T or the MeadeHarris color unit of the untreated molasses solution is taken as the basis for calculating the percentage of original color remaining, (C), and the percentage of color removed, (x). Knowing m from the weight of carbon, x/m is computed, and the results are plotted on double logarithmic paper, as recommended above.

Sanders [45, 46] has applied the adsorption isotherm to calculate the amount of carbon to be used to reach a desired degree of decolorization and also to compute the decolorization and the carbon required in countercurrent work.

Although one may read the values of r/m and C from the isotherm plot and may calculate m from the relation x+C-1 (if color is expressed as a fraction), this computation is done more easily by reference to the nomograph shown in figure 80.

This nomograph solves the equation Y/M= K(1-Y)". This is the same as r/m=kC", where the color is a fraction of the original

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FIGURE 79.—Adsorption isotherms of the same three decolorizing carbons shown in

figure 78 (plotted on a logarithmic scale).

k, A constant (value of ordinate, where log C=1); 1/n, a constant (slope of the isotherm or tangent of the angle formed by the isotherm with the log Caxis).

color, ry and C-1-y. To exemplify the use of the chart, let us suppose that the values for K and 1/n were found to be 3 and 0.610, respectively, and that it is desired to know how much carbon is necessary to remove 70 percent of the color. On figure 80 draw a straight line from 1/n=0.61 to Y=70, and extend this line to the MK axis. The line extended cuts this axis at 1.45. Since K=3, then M=1.45/3=0.483 g (or pounds) of carbon per unit volume of solution. In describing a carbon in terms of K and 1/n, it is necessary to adopt standards of mass and volume of carbon and solution, respectively.

(b) GRANULAR BONE BLACK

The sample of bone black may be pulverized and tested for decolorizing efficiency in the same manner described for the char powders. However, since the two kinds of carbon differ so greatly in grain size.

and in other properties, and since the mode of application in practice is different, the refinery chemist prefers to use a method that is more nearly representative of practical working conditions.

Experimental methods of evaluating bone chars are described by Wayne [53] and by Knowles [54], both of whom apply the char to the sugar solution on a weight basis. Blowski and Bon [49] apply the carbon on a volume basis. They place 170 ml of bone char in a 500-ml flask containing 10 ml of Filter-Cel and add 200 ml of a 47.5-Brix solution of crystallizer remelt sugar. The mixture is shaken and digested 3 hours on the water bath with 30-second periods of shaking every half hour. The mixture is decanted into paper filters and allowed to filter overnight. A blank and an arbitrary standard

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FIGURE 80.-Nomograph for calculating, from the isotherms, the amount of carbon required to reach a desired degree of decolorization.

char are submitted to the test in parallel. The color remaining in each filtrate is determined and the decolorizing efficiencies are compared with that of the arbitrary standard.

In the Spencer-Meade handbook [55] is described a procedure in which the weighed bone black is placed in cylindrical copper funnels, diameter 4 inches and height 15 inches, each provided with an outlet pipe and cock at the bottom. The char rests on a perforated copper plate covered with cloth. The funnels are placed in a water bath, provided with suitable openings for the outlet cocks and are filled to within a few inches of the top with the chars to be compared, the weight of char in each filter being the same.

A 55-Brix solution of a molasses sugar clarified by filtration with kieselguhr is used for the test. The liquor is heated to 165° F (73.9° C) and equal portions are added, little by little, to avoid air pockets. After the char is covered, the remainder of the liquor is poured into the filter. The temperature of the water bath is maintained at 160° to 170° F (71.2° to 77.2° C) for several hours, and the liquor is then drawn off through the outlet cocks. The color of the filtrates and of the untreated liquors are compared.

In this procedure it may be necessary to clarify the char filtrates, if char particles are present, by further filtration with kieselguhr, and changes in the concentration of dry substance may be detected by means of the refractometer.

11. REFERENCES

[1] K. Ventzke, Z. Ver. deut. Zucker-Ind. 10, 381 (1860); 11, 495 (1861). [2] K. Stammer, Z. Ver. deut. Zucker-Ind. 11, 41 (1861).

[3] F. J. Bates and associates, Int. Sugar J. 22, 654 (1920) (abstract).

[4] H. H. Peters and F. P. Phelps, Tech. Pap. BS 21, 261 (1927) T338.

[5] L. Eynon, Committee on Publication (1936), 7 & 8 Idol Lane, London, E. C. 3, England.

[6] K. S. Gibson, J. Opt. Soc. Am. & Rev. Sci. Instr. 10, 169 (1925); 11, 359 (1925).

[7] K. S. Gibson and H. J. McNicholas, Tech. Pap. BS 12 (1919), T119.

[8] K. S. Gibson, H. P. T. Tyndall, and H. J McNicholas, Tech. Pap. BS 13 (1920), T148.

[9] K. S. Gibson, J. Opt. Soc. Am. 24, 234 (1934).

[10] H. J. McNicholas, BS J. Research 1, 793 (1928) RP30.

[11] Spectrophotometric Equipment (Bausch & Lomb Optical Co., Rochester, N. Y.)

[12] Optical Instruments of Recent Design, Bul. 126 (The Gaertner Scientific Corporation, 1201 Wrightwood Ave., Chicago, Ill.)

[13] C. W. Keuffel, J. Opt. Soc. Am. & Rev. Sci. Instr. 11, 403 (1925).

[14] Advertising Leaflets, Palo-Myers, Inc., 81 Reade St., New York, N. Y.

[15] G. P. Meade and J. B. Harris, J. Ind. Eng. Chem. 12, 686 (1920).

[16] F. J. Bates, Bul. BS 2, 239 (1906) S34.

[17] J. F. Brewster, J. Research NBS 16, 349 (1936) RP878.

[18] J. F. Brewster, Facts About Sugar 28, 228 (1933) (abstract.)

[19] K. S. Gibson, J. Research NBS 14, 543 (1936) RP785; J. Opt. Soc. Am. 25, 131 (1935).

[20] C. Pulfrich, Z. Instrumentenk. 26, (1929). [21] Pulfrich Photometer, Advertising booklet.

New York, N. Y.)

(Carl Zeiss, Inc., 485 Fifth Ave.,

[22] E. Landt, Z. Ver. deut. Zucker-Ind. 84, 954 (1934).
[23] R. Müller, Ind. Eng. Chem., Anal. Ed. 11, 1 (1939).
[24] K. S. Gibson, NBS Letter Circular LC 473 (1936).

[25] K. Sandera, Z. Zucker-Ind. čechoslovak. Rep. 31, 261 (1927–28).
[26] P. Jackuschoff, Deut. Zucker-Ind. 56, 859 (1931).

[27] A. L. Holven and T. R. Gillett, Facts About Sugar 30, 169 (1935).

[28] J. C. Keane and B. A. Brice, Ind. Eng. Chem., Anal. Ed. 9, 258 (1937).

[29] E. Landt and H. Z. Hirschmüller, Z. Wirtschaftsgruppe Zucker-Ind. 87, 449 (1937).

[30] Th. Herke and N. Rempel, Deut. Zucker-Ind. 59, 379, 397 (1934).

[31] Brukner and Becker, Deut. Zuckerind. 59, 692 (1934).

[32] A. R. Nees, Ind. Eng. Chem., Anal. Ed. 11, 142 (1939).

[33] B. Lange, Z. Instrumentenk. 53, 344, 379 (1933).

[34] H. Hirschmüller, Dessertation, Univ. Berlin, June 10, 1938.

[35] B. Lange, Photoelemente und ihre Auwendung (J. A. Barth, Leipzig, 1936). [36] H. Krefft and E. Summerer, Das Licht 4, 1, 23, 86, 105 (1934).

[37] K. S. Gibson, J. Opt. Soc. Am. 2, 23 (1919).

[38] R. B. Withrow, C. L. Shrewsbury, and H. R. Kraybill, Ind. Eng. Chem., Anal. Ed. 8, 214 (1936).

[39] J. F. Brewster and F. P. Phelps, Ind. Eng. Chem., Anal. Ed. 2, 373 (1930). [40] H. H. Peters and F. P. Phelps, Tech. Pap. BS 21, 271 (1927) T338.

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