AbstractKrause skim‐milk powder in air of 20, 30, 40 and 50% relative humidity takes up water resulting in final percentages of moisture of, respectively, 3.5, 4.8, 6.7 and 6.4%, calculated with respect to the powder at equilibrium. In the range 15°‐25°C the equilibrium does not change with the temperature.These figures are about 1% higher than those of SuppleeG. C. Supplee, J. Dairy Sci. 9, 50 (1926).) and about 0.4% lower than those of DavisR. N. Davis, J. Dairy Sci. 22, 179 (1939).).Our data correspond exactly with the conclusion that in skim‐milk powder obtained by the usual Krause process the proportion of α‐ to β‐lactose is the same as in milk.Another conclusion is that not all the lactose is in the anhydrous state, a result which differs from that of an investigation of Tillmans and StroheckerJ. Tillmans and R. Strohecker, Z. Untersuch. Lebensm. 47, 377 (1924).). Extreme accuracy in determining the percentage of moisture is necessary in order to obtain reliable results. We worked out such a method suited t