Milk Surfaces. I. The Surface Tension of Fresh Surfaces of Milk and Certain Derivatives

Summary The vibrating-jet method of measuring surface tension was applied to milk. The surface tensions of commercially homogenized milk at 25° C. were determined at surface ages ranging from .0007 to .0265 seconds. Correction factors needed to reduce the measured surface tensions at surface ages as young as .0003 seconds to average values excluding the first two waves were nearly identical for milk and water. Any great change in the surface tension of milk relative to water therefore must have taken place before the surface age of .0003 seconds. When milk was diluted with ten parts of water, or when the casein was precipitated by saturating the milk with sodium chloride or when other proteins also were precipitated by acidifying with hydrochloric acid, large decreases of surface tension were found in the age range .001 to .01 seconds. When milk was diluted to .01 per cent or when the above filtrates were diluted to 1 per cent, decreases in surface tension could be observed by ordinary methods for periods of several hours.