334
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Literature Cited Amerine, M. A., Martini, L. P., and De Mattei, W., IND.ENQ. CHEM.,34, 152 (1942). Arbuzov, K. N., and Grebenshohikov, B. N., J . Phys. Chem. ( V .S. S. R.),10, 32 (1937). Bikerman, J. J., Tram. Faraday Soc., 34, 634 (1938). Blom, J., and Prip, P., Vochschr. Brau., 53, 11 (1936). Clark, G. L.,and Ross, S., IND. ENQ.CHEY.,32, 1594 (1940). Foulk, C. W., and Miller, J. N., Ibid., 23, 1283 (1931). Hardy, Sir William, J . Chem. SOC.,127, 1207 (1925). I Hoffmann, K., and Peter, H., Kolloid-Z., 97, 161 (1941). Lederer, E. L., Angew. Chem., 47, 121 (1934). Lederer, E. L., Seijeensieder-Ztg,, 63,331 (1936). Mischke, W.. KoZZoid-Z., 90, 77 (1940).
Vol. 15, No, 5
(11) Ostwald, Wo., and Mischke, W., Ibid., 90, 17. 205 (1940). (12) Ostwald, Wo., and Siehr, A., Ibid., 76, 33 (1936). (13) Pankhurst, K. G. A., Trans. Faraday Soc., 37,496 (1941). (14) Ross, J . , and Miles, C. D., Oil & S o a p , 18,99 (1941). (15) Ross, Sydney, paper presented before Division of Colloid Chemistry a t 103rd AMeeting of A l l ~ ~ 1 c .CHEMICAL 4~ SOCIETY, Memphis, Tenn., April, 1942. (16) Ross, Sydney, and Clark, G , L., Wallerstein Labs. Commun. S&.
Practice Brewing, No.6,46 (1939). (17) Schutz, F., Trans. Faraday SOC.,38,85 (1942). (18) Talmud, D., and Suchowolaka,ja, S., Z . phys. Chem., A154, 277 (1931).
PRESENTED before the Division of Colloid Chemistry at the 104th Meeting of the .4&fERICAXCHEMICAL SOCIETI,Buffalo, y. Y,
Baumd-Dry Substance Tables for Starch Suspensions J. E. CLEL-AND, E. E. FAUSER', AND W. R. FETZER, Union Starch and Refining Company, Granite City, Ill.
No tables for Baumkdry substance starch have been published in this country, although it is a large producer of starch. Such tables are presented for cornstarch, together with a new method for moisture on starch suspensions. The experimental evidence indicates that such tables can be constructed mathematically if the absolute density of the specific starch is known.
F
OR many years the wet-milling industry in this country has employed the hydrometer for measuring the density of starch suspensions or slurries in their manufacturing operations. Various companies have adopted dry substance tables for these Baume values, but no common table exists for use within or without the industry where starch is employed. The use of a hydrometer for the measurement of solids in a suspension or slurry may seem strange to chemists who regard it solely from the standpoint of determination of density in true solutions. I t s success in starch suspensions is based on the relatively slow settling of the starch and on the fact that the concentration of the starch suspensions a t the hydrometer bulb is substantially constant. An analyst familiar with these properties acquires the technique readily and results on a common sample agree within 0.1 B6. or 0.2 per cent dry substance. Tables have been published for the B a u m b d r y substance relationship for potato starch suspensions (4, 6, 6). Other papers have been published on the densities of the various starches (3). The purpose of this paper is to present such tables for cornstarch, known in the trade as pearl starch, for the hydrometer in use in this country-145 Modulus, standardized a t BO" F. Experimental This work is based on methods previously published on the determination of the Baumbdextrose equivalent-dry substance for corn sirup and corn sugar (1, 2) which should be 1
Present address, Goodyear Tire & Rubber Co.. Akron, Ohio.
consulted for the basic experimental methods, as only the departures from this work are discussed here. CORNSTARCH.The starch used for these tables was taken from the final washing filter in the factory. The cake from this filter is either dried t o form the pearl starch of commerce or suspended in softened water for subsequent hydrolysis to corn sirup or corn sugar. A quantity of this suspension was washed by decantation or dewatered on a Buchner funnel, washed, and finally suspended in distilled water to approximate the various densities required. The starch had a crude protein content of 0.3 per cent on a dry basis.
Baunil BY HYDROMETE:.The Baum6 readings were made at three temperatures-60 , loo", and 140" F. (l5.56', 37.7S0, and 60' C.), the temperature of the bath being maintained within *0.02" F. ( 0 . 0 1 1 O C.). Approximately a gallon (3.785 liters) of the sample was placed in a glass bottle in the water bath and the suspension was maintained by a motor-driven stirrer so adjusted that the agitation was not vigorous enough to cause air to be occluded. When the temperature of the suspension equalled that of the bath, the sample was quickly transferred to hydrom-
R DRYSCBSTANCE STARCH TABLEI. B A U M ~ - P ECENT Corresponding Gravity Specific
Baumd
(Air)
-2.01 -0.71 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00 20.00 21.00 22.00 23.00 24.00 25.00
0.9864 0.9951 1.0000 1.0069 1.0104 1.0211 1.0285 1.0358 1.0433 1.0568 1.0585 1.0663 1.0742 1.0822 1.0903 1.0986 1,1071 1.1156 1.1242 1.1330 1.1419 1.1510 1'. 1602 1.1696 1.1791 1,1888 1.1986 1.2086
60°/600 F.
... ...
0.00 1 .'78 3.55 5.33 7.11 8.89 10.66 12.44 14.22 15.99 17.77 19.55 21.32 23.10 24.88 26.66 28.43 30.21 31.99 33.76 35.54 37.32 39.09 40.87 42.65 44.43
-
1.7700
F = 1.753
100°/600 F.
140°/600 F.
F = 1,7770 F
... 0.00 1.26 3.03 4.80 6.57 8.34 10.11 11.87 13.65 15.42 17.19 18.96 20.73 22.50 24.27 26.04 27.81 29.58 31.35 23.12 24.89 26.66 88.43 40.20 41.97 43.74 45.51
0.00 2.28 3.52 5.28 7.02 8.78 10.54 12.29 14.04 15.79 17.55 19.30 21.05 22.81 24.56 26.31 28.08 29.82 31.57 33.32 35.08 36.83 38,58 40.34 42.09 43.84 45.60 47.35
May 15, 1943
ANALYTICAL EDITION
335
the stoppers to be taken as pure water-i. e., no solids. The moisture test was made on a separate bottle as before. TABLE11. CORRECT~ONS TO BE SUBTRACTED FROM ASSIGKED c. The pycnometer was used with an added feature consisting SPECIFICGRAVITY TO GIVETRUE SPECIFICGRAVITY IN VACUUM of a test tube with standard-taper joint as shown in Figure 1. Assigned The starch suspension was run into the pycnometer until it was Specific nearly full and then allowed to settle. When the top part of the Gravity Corrections t o Be Subtracted Baume (Air) 6Oo/6O0F. 10Oo/6O0 F. 14O0/6OD F. liquid was essentially clear, the stopper was inserted and the apparatus laced in the bath. After an hour the pycnometer was re-2.01 0.9864 0.00206 -0.71 0.9951 o.60io6 0.00213 movejfrom the bath and weighed. Then the stopper and outer 0.00 0.0000 0.001 11 0.00216 1.0000 cap were removed and the test tube was applied. The suspension 5.00 0.00005 0,00120 0.00233 1.0358 was shaken until uniform and a moisture determination madeIon 10.00 0.00012 0.00130 1.0742 0,00233 15.00 1.1156 0.00019 0.00143 0.00265 this material. 20.00 1.1602 0.00025 0.00154 0.00281 This method eliminated the difficulties of starch at the seals; 25.00 0.00031 0.00166 0.0029s 1.2086 the liquid that was lost through the capillary was essentially pure water; and settling was not a dominant factor, since the moisture determination was made on the suspension actually present in the pycnometer. Tests were made to estimate the error introduced TABLE 111. TEMPERATURE CORRECTIOSs TO BE ADDED by loss of the film of water left on the stopper and cap which were 1000 t o 140'to 1200 to 1200 to removed when the test tube was attached for resuspending the Baume 60' F. 60' F. 60' F. 100" F. starch. This was found to be 20 to 30 mg. on a 95- to 100-gram 0.00 0.71 1.98 1.24 0.52 sample weight. This involves an error of 0.02 to 0.03 per cent 5.00 0.69 1.92 1.20 0.51 and can be neglected for all ordinary purposes or be compensated 10.00 0.67 1.85 1.17 0.49 0.65 1.78 15.00 1.13 0.48 for in work of highest precision. 20.00 25.00
0.63 0.61
1.72 1.65
1.09 1.05
0.46 0.44
eter cylinders and five 4-ounce (0.12-liter) screw-top bottles. The former were used for the determination of BaumB by hydrometer and the latter for determination of density by pycnometer. The starch in the cylinders was kept in suspension by means of a long rod which had a perforated disk at one end, and by carefully introducing and manipulating this agitator, no air was carried into the suspension. The hydrometer to be used was kept in a cylinder of distilled water adjacent to the cylinders containing the starch suspension, and when the temperature of the starch suspension was the same as that of the bath, the hydrometer was removed, quickly wiped free from the film of water, and placed in the starch suspension. When the spindle was a t rest a small drop of methylene blue solution (in water) was added a t the stem to accentuate the meniscus and the reading made at the upper edge of the blue line around the stem. Previous work had indicated that the differences between the reading of this point and the plane surface of the liquid (correct reading) was 0.08' BB. Thus 0.08" BB. was added to the observed reading and this value appears in all tabulated data for BaumB.
DETERUINATIOX OF NOISTURE. The method used is basically the same as that employed for the determination of moisture in corn sirup and corn sugar (1) which should be consulted for details. Diatomaceous Silica,prepared Johns-Manville Hy-Flo ( 1 , 2).
Apparatus. Wide-mouth Erlenmeyer flasks, 250-ml. capacity, with 40112 standard taper, with stoppers. Pyrex test tubes 100 X 15 mm. ( 1 ) .
DENSITY BY PYCKOMETER. Settling difficulties presented a problem in the determinations of density by pycnometer and as a result three methods were used to overcome this trouble. Kone is completely free from criticism, although the latter two are regarded as more desirable. The pycnometers used have been described previously ( 2 ) . a. The 4-ounce samples mentioned above were kept in the bath while the BauniB was determined by hydrometer. Then the temperature vias raised or lowered a few degrees, depending on relationship of bath to room temperature, to compensate for heat chan es during the transfer of the sample to the pycnometer. The tottle was agitated every 5 minutes, then returned to the bath, reagitated, etc. After five such agitations, the sample was transferred rapidly to the pycnometer, stoppered, and placed in the bath which was now set a t the desired temperature. The pycnometers Lvere kept in the bath for 30 minutes, then removed and weighed. Usina this method. difficdtv was encountered at the hieher concenrrations in that starch collected a t the ground surfaces. The precision was about 0.05' BB. and as a result this method was discarded for the heavier BaumBs and method b used instead, The moisture on the starch JYas determined on one of the remaining 4-ounce samples, as described below. b. The pycnometers were filled about three-fourths full at room temperature, heated to about 130' F., and boiled very gently under high vacuum to remove occluded gas. The starch was then allowed to settle and the remaining space was filled with cool, recently boiled distilled water. The pycnometer was laced in the water bath and weighed at the end of an hour. rom this weight it was possible to calculate the specific gravity on the basis of complete suspension. This method eliminated the difficulty of the collection of starch between seals and also enabled any loss throurh the capillary of
E
FIGURE1
Procedure. Twenty-five to 35 grams of diatomaceous silica were run into duplicate flasks, the test tube was introduced, and weight constancy was obtained under oven conditions identical with those of the test. Weighings were made with an empty flask as a tare. The starch samples, either in the 4-ounce bottles or the pycnometer equipped with test tube, were shaken until homogeneous suspensions were obtained. Sample portions, sufficiently large to yield 5 to 8 grams of dry substance, were transferred quickly to the flasks by means of a pipet from which the tip had been cut. The sample was then worked into the diatomaceous silica by means of the test tube, which yielded a damp powdery mass. The flasks were placed in a vacuum oven a t 100' C., and the pressure was reduced first by an efficient. water pump until most of the water was removed and then by means of a Megavac pump. After approximately 4 hours of drying the flasks were removed
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
336
TABLE IV. BAUME-DRYSUBSTANCE STARCH (l0Oo/6O0F.. F = 1.7700, 10' hydrometer) Specific Pounds Dry Pounds per Substance Gravity Dry (Air) Substance Gallon per Gallon 8.328 0.105 1.0000 1.26 3.03 8.386 0.254 1.0069 8.445 0.405 1.0140 4.80 8.504 0.559 1.0211 6.57 8.34 8.565 0.714 1.0285
Baum6 0.00 1.00 2.00 3.00 4.00 7.00 8.00 9.00
5.00
1.0358 1.0433 1.0508 1.0585 1.0663
10.11 11.88 13.65 15.42 17.19
8.626 8.689 8.751 8.815 8.880
0.872 1.032 1.195 1.359 1.526
10.00 11.00 12.00 13.00 14.00
1.0742 1,0822 1,0903 1.0986 1,1071
18.96 20.72 22.50 24.27 26.04
8.946 9.013 9.081 9.150 9.220
1.696 1.867 2.043 2.221 2.401
15.00 16,OO 17.00 18.00 19.00
1.1156 1.1242 1.1330 1.1419 1.1510
27.81 29.58 31.34 33.11 34.88
9.291 9.362 9.436 9.510 9.586
2.584 2.769 2.957 3.148 3,344
20.00 21.00 22.00 23.00 24,OO
1.1602 1.1696 1.1791 1.1888 1.1986
36.65 38.42 40.19 41.96 43.73
9.662 9.741 9.820 9,900 9.982
3.541 3.742 3.947 4.154 4.365
25.00
1.2086
45.50
10.065
4.580
6.00
,
from the oven and cooled and the mass in the flasks was reworked into a fine powder. The flasks were returned to the oven, and a pressure of less than 1 mm. maintained until weight constancy was obtained. An overnight period has been found adequate. Because of the very hygroscopic property of dry starch, an efficirnt train ( 1 ) must be used to introduce air into the oven and the flask stoppers must be inserted immediately upon opening the oven. This method gave reproducible results within very narrow tolerance. Microscopic examination of the dried starch revealed no visible change in the granules through rupture or gelatinization. Tests indicated that oven temperatures could be carried as high as 110' C. with no appreciable effect on the results. The method of reporting data was the same as that previously used ( 2 ) . The net pycnometer weight was corrected first to vacuum. I n the case of the 60'/60° F. data, the density (vacuum) was obtained and the corresponding Baume value assigned. This procedure was changed for 140'/60° F. and 100"/60" F. data. After the net pycnometer weights had been corrected to vacuum, an additional weight correction (glass expansion and hydrometer) was added before calculating the density in order to make these values agree with the corresponding hydrometer readings. The reason for this has been previously discussed ( 2 ) . B y this correction observed Baume readings and Baume values obtained by pycnometer always agreed within 0.05' BB. and with an average deviation of 0.03 " BB. The BaumB-dry substance data mere plotted in two mays: Baume vs. dry substance and Baume us. factors. I n both cases the best curve was a straight line, as it should be if the slurry were a true suspension. The previously used method of factors was employed for purposes of tabulation. The factors were: D . S. Factor for 60"/60"F. (F6Oo/6O0F.) = __ = 1.7770 BB.
Factorfor100°/60"F. (F100"/60°F.) = BB,D's'o.71" = 1.7700 +
D.S. 2,010 = 1.753
Factor for 14Oo/6O0 F. (F140°/60" F.) = B B ,
+
Vol. 15, No. 5
In Table I, the Baumes in all cases are the observed values and the specific gravities (air) are those corresponding to the BaumBs. I n the above data the specific gravities a t 60"/60" F. in air can be converted to vacuum by the usual calculations. The 100"/60" F. and the 140"/60" F. data require not only the calculation for air to vacuum but also those for glass expansion and for hydrometer. This has been discussed previously (2) and a n abridged table (Table 11) is given here for those who may desire to express the data on some other basis. Since most Baume tests in factory processes are not made a t a fixed temperature, a table of temperature corrections is necessary (Table 111). The determination of each point in the table furnished enough data for calculation of the density of the actual starch solids. Hence a series of independent starch density values were obtained over the range of suspension gravities. These were observed to check very closely in the 60"/60" F. series and to average 1.636. Employing this value for the B a u m b dry substance relationship, a calculated table was found to check the experimental table within the limits of the experimental methods used. It would appear, therefore, that tables for water suspensions of the whole gravity range could be prepared for any starch from a n accurate density value of starch solids determined a t a single point. Each temperature, of course, would require a separate determination, A table has been prepared for general factory use based on 100" F (Table IV). I n this table the BaumBs are the observed readings, the specific gravities are those in air assigned to the Baume values and the weights per gallon are based on these specific gravities. Briefly, the corrections (Table V) mean that when the lO0"/6O0 F. table is used: for each 5" F. below 100" F., subtract 0.1" BB. from the reading; for each 4" F. above 100" F., add 0.1" BB. to the reading.
TABLEV.
TEMPERATURE CORRECTIOKS IN Bauu6
(To be added t o or subtracted from observed Baume t o adjust to 100e F.) Temperature, ---Observed Baume (10' Hydrometer)? F. 0 5 10 15 20 25 -Subtracted from Observed BaumB80 0.40 0.39 0.38 0.37 0.36 0.35 0.31 0.29 0.29 0.28 0.27 85 0.31 90 0.21 0.20 0.19 0.19 0.21 0.20 0.10 0.11 0.11 0.10 0.10 9s 0.11 7 -
104 108 112 116 120
0.09 0.19 0.30 0.41 0.52
ddded t o Observed Baume0.09 , 0.09 0 08 0.08 0.19 0.17 0.17 0.18 0.28 0.28 0.27 0.26 0.39 0.38 0.37 0.36 0.51 0.49 0.48 0.46
0.08 0.16 0.25 0.34 0.44
Conclusions Experimental results indicate that tables for BaumB-dry substance starch can be made mathematically, provided the density of any starch is known. A procedure for drying starch slurries or suspensions is presented.
Literature Cited Cleland, J. E., and Fetrer, W. R., IND. ENG.CHEM.,ANAL.ED., 13, 858-60 (1941). Fauser, E. E., Cleland, J. E., Evans, J. W., and Fetrer, W. R . , I b i d . , 15, 193 (1943). Parow, Edmund, Z. S p i r i t u s i n d . (N. F.), 30,432 (1907). Saare, Oscar, I b i d . ( N . F.), 7,550-2 (1884). Sprockhoff, I b i d . . 52, 238 (1929). Wolff, 0.. I b i d . , 58. 401 (1935).
