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A Comparison of Two Systems for Measuring Volume by Air Displacement¹

Michigan State University, East Lansing 48823

Abstract

The use of air displacement systems to measure the volume and, hence, the density and composition of live animals is discussed. A single chamber system, in which the volume of the system is changed, is compared with a double chamber system in which the subject chamber is opened to a second chamber at a different pressure. Expressions are developed for the response of each system in terms of the change in equilibrium pressure per unit change in subject volume. Results show that when the subject occupies 75% of the subject chamber volume and the second chamber in the double chamber system is 25% of the volume of the subject chamber, then the response in the single chamber system is twice that of the double chamber system. As the volume of the second chamber in the double chamber system approaches zero, the response of the double chamber system approaches that of the single chamber system.

¹ Michigan Agricultural Experiment Station Journal Article 5336. This investigation was supported in part by a grant-in-aid from The Nutrition Foundation, Inc., 99 Park Avenue, New York, N. Y.

² Present address: M. C. Franklin Laboratory, University of Sydney, Camden, N. S. W. 2570, Australia.

³ Department of Food Science and Human Nutrition.