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foam measurements; the results of a previous paper (33) offer proof that the value of Z is independent of the gas pressure, which determines the rate of formation. The first condition, that the rates of foam decomposition be identical, can never be obtained in practice; the degree of deviation between the values depends on the nature of the constituent in the surface layer. As already stated by Aleinikov ( I ) , the coagulation of a dynamic foam involves the rupture of newly formed surfaces, whereas the coagulation of a static foam involves the rupture of surfaces which have had time to age and, moreover, continue to age even while measurements are being made. While this factor may not be significant in many cases, it certainly has an effect in the case of egg albumin foams where, as shown by Bull (18), denaturation, and possibly ultimate coagulation, takes place on the surface layer. It has also been claimed that these changes in the surface layers of proteins are not immediate but take place over a period amounting to several minutes (66, 89). That the aging of solutions affects the foaminess can be observed from the results of Table IIB, where the solution was aged under conditions which tended to minimize any chemical reaction. A much greater effect would be expected when the aging of the solution takes place in the large surface areas which exist in the foam. The result of denaturation appears to be an increase in the foaming property of the protein sol, as manifested by the increase in Z for aged solution (Table IIB) and the continuous increase of B (Table IIIB) as the foam ages. This is in accordance with the results of Loughlin (97) who found an increase in the capillary activity of protein sols on denaturation. The work of Duce (14) on the aging of protein sols showed a series of maximum and minimum changes in the values of surface tension and viscosity as the sol aged. It is well known that these properties also influence the foaminess. I n such circumstances a correlation between the static and dynamic foam measurements cannot be expected. I n his work on the unit of foaminess for dynamic foams, Bikerman (7) demonstrated that the value of Z was independent of the rate of flow of the gas through the membranein other words, independent of the rate of formation of the foam-but his investigation was conducted on air foams of butyl alcohol solutions where no reaction took place between the constituents in the two phases, In the case of carbon dioxide foams of egg albumin, we must postulate a reaction between the gas and the protein in order to account for the fact that dynamic foam measurements show the carbon dioxide foam of egg albumin to be more stable than the air foam, whereas the static foam measurements show just the opposite result. The bubbles in the carbon dioxide foam are much finer than in the air foam; consequently, the volume of foam per unit volume of gas would be slightly greater. At the same time, some of the gas is absorbed by the protein sol and hence plays no part in the tormation of the foam. The result is that even when the same rate of flow of gas through the membrane is used, the rate of formation of the foam in carbon dioxide differs from the valqe it has when the gas is air. This violates the second condition for a parity in results for the two methods. The measurements by the static method indicate the difference in the rates of foam decomposition, and the measurements by the dynamic method indicate that the difference in the rates of formation is more than enough to overcome the difference in the decomposition rates between air and carbon dioxide foams of egg albumin. There can be no doubt that the use of air and carbon dioxide foams of egg albumin exhibits the deviation between the two basic methods of foam measurement to a maximum degree. The results of the present study show that methods of foam measurement can be correlated, even when the foam is produced in different ways, if only static methods of measurement are used. In this connection, a unit of foaminess for static
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foams is provided. The work of Bikerman (7) has provided a comparable unit for dynamic foam measurements. It is now apparent that with these two broad distinctions all the methods of foam measurement can be classified and methods within each group correlated, apparent inconsistencies between the two classes can be explained, and, i t is believed, a sounder bask established for the development of further methods.
Literature Cited (1) Aleinikov, N. A., Kolloid-Beihefte, 36,82 (1932). (2) Arbuzov, K. N., and Grebenshchikov, B. N., J . Phys. Chem. (U. S. S. R.), 10, 32 (1937). (3) Astbury, W. T., Bell, F. O., Gorter, E., and Ormondt, I., Nature, 142, 33 (1938). (4) Bailey, M. I., IND. ENQ.CHEM.,27, 973 (1935). ( 5 ) Barmore, M., Colo. Agr. Expt. Sta., Tech. Bull. 9 (1934). (6) Bernhart, F. W., and Arnow, L. E., J. Phus. Chem., 43, 733 (1939). (7) Bikerman, J. J., Trans. Favaday SOC.,34, 634 (1938). (8) Blom, J., J. Inst. Brewing, 43, 251 (1937). (9) Blom, J., Petit j . brasseur, 42,388 (1934). (10) Blom, J., and Prip, P., Wochschr.Brau., 53, 11 (1936). (11) Blom, J., Prip, P., and Jacobsen, J.,Ibid., 53,25 (1936). (12) Bull, H. B., J. Bid. Chem., 123, 17 (1938). (13) Chang, H.-Y., and Hsieh, M.-S., J. Chinese Chem. Soc., 2, 117 (1934). (14) Duoe, W., Boll. SOC. {tal. bid. sper., 10, 977 (1935). (15) Ferguson, J. K. W., and Roughton, F. J. W., J . Physiol., 83, 68 (1934). (16) Foulk, C. W., and Miller, J. N., IND.ENQ.CEEM.,23, 1283 (1931). 33,1125 (1937). (17) Gorter, E., Trans. Faraday SOC., (18) Gregorie, E., Compt. rend. soc. bid., 99, 1227 (1928). I Groak, B., Biochem. Z., 196, 478 (1928). I Hansley, V. L., Ohio State Univ., doctor’s dissertation, 1928. I Helm, E., Wochschr.Brau.. 50.241 (1933). Helm, E., and Riohardt, O., J: Inst.’Bre&ng, 42, 191 (1936). Laufer, S., and Ziliotto, H., Am. Brewer, 72, No. 8, 25 (1939). Ibid., 72, No. 9, 33 (1939). Lederer, E. L., Seifensieder-Ztg., 63, 331 (1936). Lee, W.-Y., and Hsien, W., Chinese J. Physiol., 6, 307 (1932). Loughlin, W. J., Biochem. J . , 27,97 (1933). Mellanly, J., and Thomas, C. J., J. Physiol., 54, 178 (1920). Neurath, H., J.Phys. Chem., 40, 361 (1936). Ostwald, W., and Siehr, A., Kolloid-Z., 76,33 (1936). Pauli, W., Biochem. Z., 152, 360 (1924). Richards, C. W., and McFail, L. W., Paper Trade J . , 97, No. 1, 29 (1933). Ross, S., and Clark, G. L., Wallerstein Labs. Commun. Sci. Practice Brewing, No. 6,46 (1939). Schuster, K., and Mischke, W., Wochschr.Brau., 54, 177 (1937). Stady, W. C., and O’Brien, H., J. Bid. Chem., 112, 723 (1936); 117, 439 (1937). Westelaken, E”. P. van der, and McCormack, R. H., Am. Brewer, 69, No. 7, 24 (1936). Williams, H. E., IND. ENG.CHEM., 18, 361 (1926).
Correspondence-Evaluation of Nitrocellulose Lacquer Solvents SIR: A statement in our article [IND. ENG. CHEM.,32, 78 (1940)] regarding the mixed aromatic-aliphatic naphtha used indicates that it is “a commercial material with a distillation range of 95-132’ C., containing approximately 30 per cent aromatics”. Recently we have been informed that considerable improvement in the product has been made during the last few years. The sample in question, used throughout our work, was procured a little over four years ago. Its aromatic content was based upon the dimethyl sulfate solubility of the material, a method generally accepted at that time. V. W. WAREAND W. M. BRUNER
