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search and Nutrition Laboratories who contributed their efforts to this work. LITERATURE CITED
(1) Am. Assoc. of Cereal Chem., Cereal Laboratory Methods, 4th ed., p. 47,Lincoln, Nebr., 1941. (2) W. R., Bull. Health Organization League Nations, 9, . . Aykroyd, . 342 (1940-41). (3) Dann, W. J., and Handler, P., J. Biol. Chem., 140,201 (1941). (4) Feinstein. L.. Science. 101,675 (1945). (5) Hennessy, D. J., IND. Eao. CHEM.,ANAL.ED.,13,216 (1941). (6) Kik, M. C., Cereal Chem., 20,103 (1943). (7) Kik, M.C.,and Van Landingham, F. B., Ibid., 20,563 (1943). (8) Ibid., 21, 154 (1944). f~, 9) Kik. M. C.. and Williams, R. R.. Natl. Research Council, BUZZ. ii2 (1945). (10) Melnick, D., Hochberg, M., and Oser, B. L., J . Nutrition, 30,
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Figure 10. Rapid Iodine Test for Roche Enriched Rice White premix kernels are liot darkened by the etarch-iodine reaction because of their protective, water-repellent coating.
enriched white rice loses most of its small content of 'thiamine, niacin, and iron readily, even with gentle washing methods. The content in white rice is therefore disregarded in preparing enriched rice, reliance being placed entirely on the content in the premix. Studies of growth and reproduction in rats have demonstrated that massive amounts of the premix are tolerated without ill effect. Further studies with rats showed that the thiamine in the raw premix is readily available for growth. Both the thiamine and niacin in cooked enriched rice are completely available to humans, as demonstrated by quantitative measurements with the human bioassay technique.
A 945). -.7 I1 \_ ---,-
(11) Oser, B.L., Melnick, D., and Hochberg, M., IND. E N ~~ .H E M . , ANAL.ED., 17,405 (1945). 112) . , Perlzweia, W. A., Levy, E. D., and Sarett, A. P., J . Biol. Chem., 136,729 (1940). (13) Rubin, S. H., and De Ritter, E., Ibid., 158,639 (1945). (14)Rubin, S. H., De Ritter, E., Schuman, R. L., and Bauernfeind, J . C., IND. ENG.CHEM.,ANAL.ED.,17,136 (1945). (15) S. C.Legislature Act, H.R. Bill 347,Senate,Bill 382,approved by Governor April 14, 1943. (16) Swaminathan, M.,Indian J . Med. Research, 29,83 (1941). (17) Ibid., 30,409 (1942). (18) U.9. Army Cooking Manual TM-10-405,p. 197,April, 1942. (19) U.S. Pharmacbpeia XII, p. 625,Easton, Pa., Mack Printing Co., 1942. (20) Ibid., 1st Supplement, p. 75 (1944). (21) Williams, R.R.. and Spies, T. D., "Vitamin Bi in Medicine", p. 313,New York, Maimillan Co., 1938. (22) Williams, V. R., and Fieger, E. A., Cereal Chem., 21, 540 (1944). (23) Williams, V. R.,Knox, W. C., and Fieger, E. A., 20, 560 (1943). .
ACKNOWLEDGMENT
The authors wish t o express their gratitude t o L. Hodax for the photographs and t o the yarious members of the Applied Re-
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Drying Oil and Oleoresinous Varnish Films INCREASE IN ACIDITY ON AGING VINCENT J. FRILETTE Ridbo Laboratories, Inc., Paterson, N. J .
A
method is described for accurately determining the acid number of an oil or oleoresinous varnish film. The method is similar to an ordinary acid titration, but is on a semimicro scale. The acidity of oils and oleoresinous varnish films was studied by this method. In all cases a large increase in acidity occurred with aging. Linseed oil films showed much larger increases than tung oil films,
and oleoresinous varnish films showed much smaller increases than the corresponding oil film. It was also found that while the acid number increased, the alkali resistance decreased. For several oleoresinous varnish films the alkali resistance of the films could be directly correlated with the acid number 6f the films; the age of the films was thus eliminated as a factor.
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which occur during the useful life of the film. Chemists have concerned themselves mainly with reactions in the first two categories. Many problems remain t o be solved, but considerable success has been achieved in correlating technical and chemical properties. The chemical changes in the third, or aging period, are by far the most important technically, for these changes determine how well the film will fulfill its purpose. Numerous practical tests have been developed t o evaluate the suitability of films for varipus applications; among them are
chemistry involved in the drying of oil and oleoresinous varnish films has been the subject of much study.' The problem is difficult 'because the chemistry is known t o be involved, and because it is difficult t o investigate these films by chemical treatment once gelation has taken place. The changes in chemical and physical properties of oleoresinous coatings may be divided into three categories: (1) those which occur in preparing the coating; (2) those which occur between the time the coating is applied and the time i t has reached the usefully "dry" stage (usually less than 48 hours); and (3) those
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YO^. 38, NO, 51
DETEH.WIKATIOi\ OF ACIDITY
hardness measurements, water, soap, and alkali resistance tests, and the various accelerated aging test,s. These practical tests are, for the most part, devoid of chemical significance and consequently are not recognized as yielding reliable informat ion for the prediction of actua.1behavior. The final tests for this quality are usually time-consuming exposures under conditions of actual use; some of them last for years. The resolution of the tlifficulties arising in attempts t o evaluate oleoresinous coatings must, then, lie in a bett,cr understanding of the fundamental chemical changes involved in the aging period, toget'her with a n elaboration of the chemical significiance of the practical trsti o o v in use
.i semimicro technique for t,itrating the acid in iiisulutiii~f i l t i i bvas developed, by which det'erminatious could be duplic~:rtc~tl t 1) 0.1 acid number unit, The titrations require more tinit, 1liitii :III ordimry determination twrause of the necessity foi, t i tr:i 1 irip :t solid phase. A portion of the dried film is renioved from the FJ;IIII'I \I i t I, :i razor hlacie and rolled together with a spatula. .I 3 0 1-0nip. sample is weighed and t,ransferred to a 25-ml. Erlenri having a ground-glass stopperj and 5 mi. of a 1 : l niixturts o4 lwnzene and alcohol art> added. A 0.01%, alcoholic rolutiori of indicat,or. l ' l i ( > t i ( i l IYctoria Blue R (0.5 ml.) is thrn added atiort, qinw i t i h (11,phthalein cannot be used i n this dct stroycd b y the peroxides iii t tic film; resistant to oxidation, arid has an rnd p phthalein.) The mixture i.Q then titrated hydroxide in a I(och microbuwt. The first end points v a r i i . t i rapidly owing to diffusion of sodium ions into the untliascilwil portion of the film. Small portjorts of alkali are added a:: tht' i * i i i i prepoint fa.des, unt,il the stable anti point is reached. TTVU vautions must he observed during the titration: (1) The fl must be warmed in a hot water bath at, each end point in ordcsr t o distinguish fading due to car.bon dioxide absorption from fading due to continued neiitralizatioii: a t the true end point' any fadinp n-hich occurs may be reversid by n-arming to expel excess carbor: dioxide, and this revr1w liould he possible after an interval of a: lrast 10 minutes. (21 i e - s ;iJkali 3liould not be added kieyonti
3,
30 D I F F U S I O N TiPE ( H R 9
Figure 1. Attaiunlerit of True End Point
('hemists Iiave recognized. in R gi:iiertil wayj thtit' \\hili. films become useful on dryirig, the chemical changes involveti in drying do not stop abruptly a t t,his point but, continw for a11 indefinit t: period. Unfortunately, overemphasis 011 thr colloidal rhanges ohserwcl in aging films has obscwecl the fact that the transformations have t,heir root in thcl changing chemical naturc' of t h e film. The x o r k of nunierous authors (1, 6 , 7 , 8) h;is s l i o ~ v iilie ~ role of aging in thta permeability and sn-ellinp characteristics of paint films ill water. Similar relation;. t)c.tu-een the a,ge of films and their hardness, adhesion, and other technical properties art' generally recognized. Much attention has been directed to the relation between water transmission chararteristics ant1 the successful funct,ioning of the film :is ii coating (.b, the behavior of films in water and alkalirir solutions of the properties which shon drastic changes with t h e ] ) a s s age of time. It has been known for some time that films evolvc n
