November 15, 1942
ANALYTICAL EDITION
TABLE IV. WEIGHTLoss AND GAINBETWEEN VACUUM DRYING AT 135' C. AND DRYINGOVER CONCENTRATED SULFURIC ACID IN DESICCATORS
Product Corn Acid-modification, 60 fluidity Acid-modification, 90 fluidity White corn dextrin Canary dextrin British gum Chlorinated starch Hypochloriteoxidized starch Tapioca 0 Gain.
.
Loss in Wei ht on Gain in Weight on Transfer of itarch Replacement of VacDried over Concen- uum-Dried Samples trated HB04 to (135' C.) in DesiccaVacuum Oven at tors over Concentrated Loss in 135' C. &SO4 Recoverv % % % 1.43 1.36 0.07 1.40
1.49
0.09O
1.21 1.65 1.03 1.41 1.41
1.15 1.19 1.01 1.37 1.43
0.06 0.46 0.02 0.04 0.02"
1.65 1.00
0.84
0.81
0.99
0.01
845
Starch is extremely hygroscopic. For this reason, the air used to replace the vacuum in the oven should be passed through a train as follows: Two 19-liter (%gallon) bottles, in series, each containing 2.5 to 5 cm. (I to 2 inches) of concentrated sulfuric acid; drying tower filled with glass wool; and preferably another tower filled with Drierite. The A. 0. A. C. oven tolerance of a pressure of 25 mm. or less of mercury is too great. The oven should have a well-seated door which will retain t,he vacuum for several hours after the pump is stopped. Otherwise, a slight leak of atmospheric air will occur, resulting in low moisture data. The period of drging should be continued until constancy ia obtained.
Acknowledgment The authors' thanks are due t o the Corn Industries Research Foundation for permission t o publish the work.
Literature Cited TABLEV.
ADSORP'I'ION O F WATER BY
PRODUCTS
VACUUM-DRIED S'I'ARCH
Moisture Adsorbed by Vacuum-Dried Samples (Wet Basis) Product 1 hour 2 hours 3 hours 6 hours 24 hours % % % % % 6.4 7.4 9.0 10.8 11.8 Cornstarch 4.5 0.2 7.7 9.3 10.3 90 fluidity starch 9.8 White corn dextrin 5 . 1 0.8 8.0 9.0 9.2 Canarydextrin 4.5 5.8 6.8 7.9
With increasing modification the sorptive capacity of starch decreases-that is, the modified products are less hygroscopic. As shown in Table VI, although the modified products retain less water, the water that is held is retained with equal or greater tenacity than the water held b y the original cornstarch. These data show that canary dextrin holds the least moisture and retains i t with the weakest tenacity. T h e white corn dextrin retains its moisture with the greatest tenacity. More critical studies are now under way t o determine the relation of the sorptive capacity of starches to their properties.
(1) Am. Assoc. Cereal Chemists, "Cereal Laboratory LMethods", p. 21. Lincoln, Nebr., 1941. (2) Bidwell, G. L., and Sterling, W. F., IND.ENQ.CHEM.,17, 147 (1925). (3) Block, M.,Compt. rend., 118, 146 (1894). (4) Cleland, J . E., and Fetzer, W. R., IND. ENQ.CHEM.,ANAL.ED., 13,858-60 (1941); 14, 27-30, 124-7 (1942). (5) Fairbrother, T. H., and Wood, R. J., Ind. Chemist, 6, 442 (1930). (6) Fetzer, W. R., and Evans, J. W., IND.ENQ.CHEM.,ANAL.ED.. 7, 41 (1935). (7) Gortner, R. A., "Outlines of Biochemistry", New York, John Wiley & Sons, 1938. (8) Halvorson, H. A,, J. Assoc. Oficial Agr. Chem., 20, 435 (1937). (9) Hoffman, J. F., and Schulze, J. H., Wochschr. Brau., 20, 217 (1903). (10) Kent-Jones, D. W., "Modern Cereal Chemistry", Liverpool, Northern Publishing Co., 1939. (11) Maquenne, M.L., Cornpl. rend., 141, 609 (1905). (12) Nelson, 0. A., and Hulett, G. A., IND.ENQ.C H ~ M .12, , 40 (1920). (13) Nowsk, G., and Enders, C., Chem. Zentr., 11, 202 (1936). (14) Sair, L., and Fetzer, W. R., Cered Chem., 19, 033 (1942). (15) Snyder, H., and Sullivan, Betty, IND. ENG.CHEM.,18, 272 (1926). (16) Zerewitinoff. T., 2. anal. Chem., 50, 680 (1911).
WITH WHICHSTARCHES RETAIN MOISTURE TABLEVI. TENACITY
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Moisture Retained (Vacuum at 100' C. 0%) 24 hours, air oven, Plus 24 hours, Plus 100 hours, air oven, loOD C. 70' C. in dry air 70' C . % % % Cornstarch 32.8 16.5 7.6 90 fluidity starch 34.8 17.2 8.6 White corn dextrin 34.8 17.7 9.1 Canary dextrin 30.2 13.8 6.9 Product
Conclusions Either of two moisture methods is suitable as a reference method for determining moisture in starch and its modifications. These two methods are the toluene distillation procedure, and the vacuum-oven method at 100" C. Rapid oven procedures using temperatures as high as 140" C., based on these methods, should prove reliable for most starch products. Care must be exercised, however, in drying highly acid modified starch and the hypochlorite-oxidized products a t temperatures higher than 100" C. The official Corn Industries Research Foundation toluene distillation method for corn and its feed products (14) is equally suitable for starch products. The recommended official C. I. R. F. reference 100" C. vacuum method for starch products is essentially similar to the A. 0. A. C. vacuum-oven method for wheat flour, with the following modifications :
Insulation for Necks of Wash Bottles JACOB MIZROCH Federal Works Agency, Public Roads Administration. Washington, D. C.
I
N THE Subgrade Laboratory, Division of Tests, Public Roads Administration, necks of wash bottles containing hot liquids had been insulated by a wrapping of thin sheet asbestos. A serious drawback is the tendency of the asbestos to crumble with use, leading t o the danger of asbestos particles falling into precipitates being washed. Bottlenecks insulated by the following procedure have been used daily for over two years without sign of deterioration. The neck of the wash bottle is snugly wound with a wetted thin asbestos strip about 2 inches wide, and the bottle is set aside to dry overnight. Bakelite lacquer (BL 3128, B 57) is then brushed on the dry asbestos, allowed to air-dry for an hour, and baked st 110' C. for 4 hours,
