The principles of ultrafiltration as applied in biological studies

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Abstract
Employing the new series of graded collodion membranes described by the author (See B. A. 6 (2) : Entry 4414), the influences exerted on the course of filtration by the several factors, concentration of disperse phase, pH, applied pressure, and volume filtered, are investigated. Data are given for typical colloidal dyes, metal sols, protein solutions, and suspensions of bacteria and viruses. The fact that a membrane invariably proves more efficient in retaining dispersed particles than would be expected on the basis of a comparison of the estimated size of its pores with the size of the retained particles in a simple sieving process is explained in terms of adsorption of the disperse phase on the walls of the pores, which thereby become narrowed. Capillary-active sub stances facilitate filtration by minimizing this adsorption, being themselves preferentially adsorbed. Use of an empirical correction factor derived from filtrations of systems of known particle size has enabled the sizes of particles in other disperse systems to be estimated from the av. pore diam. of the limiting membrane, which, under conditions otherwise most favorable for filtration, just completely retains all the dispersed particles. The sizes of viruses and bacteriophages determined by this method are shown to be in good agreement with the values furnished by other physical methods.

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