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The magnetization curves of colloidal magnetite (Fe₃O₄) and colloidal siderac (-Fe₂O₃) have been determined by a null method for fields from 0 to 400 gauss. The measured curves have been found to agree with a theoretical curve based on the following assumptions: (1) Each colloid particle is a permanent magnet. This assumption is in accord with a prediction of the theory of ferromagnetism that small ferromagnetic particles be single magnetic domains. (2) There exists a distribution in the size of the particle moments similar to the weight distributions which have been found for other colloids. (3) The particles behave as the molecules of a classical paramagnetic gas. On this basis the average particle moment is found to be 5. 2 (10) ^-16 for the magnetite sol and 7. 4 (10) ^-16 for the siderac sol. Several other quantities related to the colloids are briefly discussed.
W. C. Elmore (1938) studied this question.