Donnan pipette

The Donnan pipette method can be very useful for comparing a number of detergents or for plotting the surface tension in relation to the concentration curve, but it fails to give all the information required because other factors such as redeposition must be taken into account in assessing the efficiency of a scouring agent. 

From the foregoing considerations it will be apparent that the lower the surface tension at the oil/water interface, the smaller will be the size of the drops of oil formed in an emulsion. Donnan s drop-number method is a simple and convenient means of determining or comparing oil/detergent solution interfacial surface tension. The apparatus is shown in Fig. 9.12, in which a pipette A of about 5 ml capacity is provided with a capillary tube B... 

Frederick G rge Donnan (Colombo, Ceylon, 6 September 1870-Canterbury, 16 December 1956), a pupil of Ostwald and van t Hoff, was professor of physical chemistry in Liverpool (1910-13) and succeeded Ramsay as professor of chemistry in University College, London (1913-37). He gave the theory of the Hall and Thomson effects for solutions of an electrolyte, the second for two solutions in contact at different temperatures. He devised a drop pipette for investigating the dispersion of oils in alkali and soap solutions. Spring proved that the detergent action of soap in removing particles of dirt depends on peptisation by adsorption of soap at the interface. The use of salts of long-chain fatty acids as detei ents stems from researches by Reychler. ... 

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