342. A note on the density of full-cream milk solids

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Abstract
A knowledge of the density of air-free milk solids is required for calculation of the quantity of oxygen originally enclosed in sealed cans containing milk powder, and for conversion of percentages of oxygen obtained by analysis of the headspace gas to absolute units. Determination of this figure is a matter of some difficulty owing to the presence of entrapped ‘air’ in the spray-dried product. In the liquid displacement method there is also a danger of error due to incomplete ‘wetting’ of the particles, or to solution of one or other constituent of the powder, while in the gas-displacement method error may be introduced by solution or adsorption of the gas by the powder. Lea, Moran & Smith(1) obtained values of 1·29 by a pyknometer method with ethylene glycol, and 1·31–1·32 by a nitrogen displacement method for full-cream solids containing 27% of fat. Muers & Anderson(2), on the other hand, reported values of 1·26–1·28 by a liquid-displacement method using propylalcohol. Further determinations have therefore been made by various modifications of all these methods.