ANALYTICAL CHEMISTRY
1498
A o FLASK E X P O S E D T O LIGHT
of L A B O R A T O R Y
20%-OOl
C-0.01
--+
SAMPLE 35.9% PURE M KzFe01 IN 3 M KOH 2573. SAMPLE 95.9% PURE
M KzFeOi I N 3 M KOH 25%. SAMPLE 89% PURE
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1
instability of solutions of ferrate in 3 J f potassium hydroxide, the authors believe that the differences are not significant. The influence of light on the decomposition of the 0.010 11 and 0.0019 M aqueous potassium ferrate was negligible within the limits of the experimental error (approuniately 1%) over a 2hour period.
effect on the decomposition rate over at, least a 2-hour period. The greater stabilit'y of more dilute solutions was confirmed.
I
~~
The result^ in Figure 2 show that light, has a negligible effecton solutions of potassium ferrate in 3 and 6 Jf potassium hydroxide. The authors have no satisfactory explanation for the greater differences in curves B of Figure 2, but in view of the
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(3) Schreyer, J. M., Thompson, 6. IT.,and Ockerman, L. T., Ibid.,
22,1426 (1950). (4) Thompson, G. IT,, Ockernlan, L, T., and Schreyer,J. Chem. SOC., 73, 1370 (1951).
J.
Srn.
R~~~~~~~ for review lRIrtrch 27, 1 s ~ ~Accepted . 11ay 22. 1952.
Rapid Approximate Method for Determination of Moisture In Pressed Beet Pulp R . H. COTTON, W. A. HARRIS, L. P. ORLEANS,
AND GUY ROR4BIIUGH Holly Sugar Corp., Colorado Springs, Colo.
E E T pulp, the by-product from the diffusion of sugar from beet cossettes during sugar manufacture, comes from the diffusion battery with a moisture content of a t least 95%. Usual practice involves dewatering over a screen and, where dehydration of the pulp is practiced, final pressing t o reduce the moisture content to 80 to 86%. Old presses, or presses improperly adjusted, will deliver pulp having moisture contents as high as 90%. Where several presses operate t o remove water from beet pulp prior t o dehydration, a rapid means of evaluating individual press performance is needed. A press which one day mill produce pulp at 85% moisture may give pulp a t 88% the nevt dav. This corresponds t o a change of 5.66 to 7.32 in ratio of water t o dry matter. In other words, the amount of water to be evaporated per pound of dry matter increases 29y0 when pressed pulp moisture goes from 85 to 88%. The present paper deals with a simple control method allowing operators to deteiniine moisture in approximately 6 minutes. Data are given on the correlation between the rapid method and the oven-dry method, ab well as on comparisons of reproducibility of the two procedures. The basis of the present analytical method is the release of moisture from pressed pulp by contact with molasses. This is followed by a final pressing in a simple potato ricer. The volume of liquid released by the ricer is directly related to the moisture content of the pulp. PROCEDURE
Keigh 200 grams of pressed beet pulp into a beaker and weigh into the beaker 200 grams of molasses a t room temperature. Xix manually n-ith a V-shaped wire for 1 minute. Place contents of the beaker in the potato ricer (see Figure 1). Press for exactly 2 minutes, using the weight as a source of pressure. Catch the press liquor in a 250-ml. graduate. Record volume of press liquor Read moisture content of pulp from a plot of press volume versus moisture, such as Figure 2.
APPARATUS
The basic unit of the apparatus is a household potato ricer consisting of a perforated basket ( erforations 2 mm. or 3 / / : 9 inrh in diameter), a plunger with attacged lever, and fulcrum. Attached to the end of the lever is a 20-pound weight so t h a t constant pressure can be applied during each moisture determination. The ricer is mounted on a stand. A funnel below the screen leads the press liquor into a graduate (Figure 1). RESULTS AND DISCUSSION
Figure 2 represents data from 95 determinations of pressliquor volume versus moisture determined by oven drying at 100O C. with a vacuum of 15 inches of mercury to constant weight. The coefficient of correlation ( 2 ) betm-een press-liquor volume and per cent moisture obtained from the 95 comparisons !vas 0.9664, a very high degree of correlation. Figure 2 is based on the regression calculated from the correlation coefficient, y = 60.23 0.140iz where y = moisture content and x = press volume ( 3 ) . Once a correlation was established the data n+ereanalyzed in order t o compare the precision of the new method compared to the oven-dry procedure. Table I gives an experiment comparing press volume with moisture determined by oven drying. Table I1 gives standard deviations ( 1 ) from 10 experiments, including the one in Table I, comparing press volume with ovendry moist,ure determinations; each experiment consisted of from 4 to 12 replicate determinations on a given sample of pulp. The average of the standard deviations for moisture content by the two methods was approsimately the same, 0.1594 and 0.1489. The rapid met,hod is, t,herefore, as precise as the oven-dry procedure. I t has the advantage of speed. Furthermore, a foreman can use it right in the pulp dryer building and immediately spot a press that is improperly adjusted. Only occasional checks
+
1499
V O L U M E 2 4 , N O . 9, S E P T E M B E R 1 9 5 2
+
Table I.
Comparison of Moisture Content Determined by Oven Drying and by Rapid ;\lethod (Experiment S o . 5 )
u,Aloisture Rcijlicate S o .
z, Liquid Pressed from Pull,, 111.
1 2 3
i
h
4 10
.\lean Standard dr\-iati o n " 1. = 60.23
+
Determined by Oren Method, 5;
Y ,Moisture Calculated by Rapid Methoda, %b
u -
209 206 209 209 208 207 209 208 208 208
89.5 89.3 89.6 89.5 89.5 89.3 89.4 89.2 89.t 84 3
89,64 89.21 89.64 89.61 89.50 89.35 89 64 89.50 89.50 89.50
1-0 14 0.09 -0 04 -0.14 0.20 0.15 -0.24 0.00 0.20 - 0 20
208.1
89.48
89.512
-0
0 9434 0.1407.r.
0.1166
03
,1356
by a chemist are needed t o be sure the method is behaving satisfactorily. The curve in Figure 2 is based on determinations made between December H a n d 23, 1951, at the Torrington, Wyo., f a c t o r y . During this pel iod six calibrations were made on separate occasions. h sample of pulp, lightly pressed in a hando p e r a t e d screnpress was progressively pressed d o r n to a low moisture Figure 1. Apparatirh for Rapid level while samples AIoisture Determination were obtained for determinations by both procedures. I n all c a w the data closely adhered t o a straight line but the position of the line varied slightly in each caee. For comparative work a curve such as Figure 2 should be adequate, while frequent calibrations (perhaps every few days) Rould give greater accuracy. This is especially true when the natute of the beets processed appears to change. For example, when all the data taken from Soveniber 2 t o December 23 are uceti (154 comparisons) the correlation coefficient x a s somewhat Iont3r, 0.9531, and the equation was changed to y = 58 34
+
Table 11. Standard Deviations from Ten Experiments Comparing Moisture Content by Oven Drying and by Rapid Rlethod
____ Eipt.
No. of
So.
Reiilications 12 10 10 10
10 10 10 10
lotal Iverapc
4 10 9
95
Liquid pressed f r o m pulp, nil. 1 0104 0 5385 0 7000 1 2206 0 9434 1 0198 1 1136 0 8660 1 9209 0 4714
9.8046 0,98046
Standard Deviation lloisture XIoisturcx determined by calculated b y oven method, % rapid method, ";
0 2291 0.0917 0.1204 0,3470 0.1166 0 1342 0 1600 0 1480 0 0748 0.1723 1.5941
0.15911
0.1407~ 0.1486~. This compares with 0.9664 and y = 60.23 derived from the data obtained Decembe] 18 to 23. Thus, when maximum speed is desired tbe method, though precise, may be only approximate unless the calibration curve is carefully checked. Occasionally difficulty is encountered in reading the volume in the graduate due t o foaming of the press liquor. Addition of 5 to 10 ml. of ethyl ether t o t h e graduate will rapidly dissipate t h e foam t o allow a clear reading a t the interface of the press liquor and ether layers Figure 3 gives variations in press liquor volume as affected by differences in the percentage solids in molasses used. Variations with percentage solids are evidently slight. Obviously, greatest precision is t o be obtained through use of one standard molasses throughout a beet rampaign.
Figure 2.
Relationship between Liquor Press Yolume and Per Cent Moisture in Pulp
PERCENT MOLASSES SOLIDS DETERMINED BY REFRACTWXTER
Figure 3.
Effect of Per Cent Molasses Solids on Press Liquor
Pulp from the presses a t Torrington had a temperature of 48" to 50" C. By the time a sample was taken and placed in a large Mason jar the temperature was usually 40" C., or lower, since the pulp was taken from the dryer feed scroll some distance from the press. If pulp is t o be sampled directly a t the press, more work i d 1 be needed on the effect of temperature on press liquor volume. Under Torrington conditions, temperature variations between 23" and 40" C. did not measurably affect the precision of the method. LITERATURE CITED (1) Peters, C. C., and Van Voorhis, W. R., "Statistical Procedures and Their Mathematical Bases," p. 68, New York and London,
1,4895 0.14895
McGraw-Hill Book Co., 1940. (2) Ibid., p. 99. (3) I b i d . , p. 111. RECEIVEDfor review March 24, 1952. dccepted May 22, 1952. Presented before t h e Division of Sugar Chemistry at t h e 121st Meeting of t h e ~ I E R I C I N CHEMICAL S O C I E T Y , Milwaukee, 1%.
