As an initial step in developing a more complete understanding of sedimentation in concentrated suspensions of fine powders, a study is presented of sedimentation in a simple system, under conditions of laminar flow. The effect of concentration on the rate of fall of uniform well-dispersed spheres is investigated both theoretically and experimentally. Tests with suspensions of tapioca particles in oil provide empirical solutions of functions of concentration left undetermined by the theoretical analysis. Tests with fairly uniform microscopic glass spheres support the conclusions drawn from the tests with the larger tapioca particles..HAROLD H. STEINOUR, Portland Cement Association, Chicago, 111. THIS article is the first of a series on sedimentation phenomena.

rently amorphous substances, were found on the surface of beads of vitreous compositions of PaOs/CaO mole ratio 1.4-1.9; these compositions had been made by reaction of rock phosphate with P205 in excess and had been stored in capped bottles in the labora-

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This paper is a further contribution to the interpretation of this potential of sulfur dioxide, and of its behavior as an oxidizing and reducing agent. The experiments refer chiefly to the potentials exhibited at a platinized platinum electrode by a half-cell with various concentrations of sulfite and hydrogen ion in the presence of various other substances, and under different conditions of agitation and temperature. This halfcell was measured in combination with a hydrogen half-cell in which nearly the same hydrogen-ion concentration prevailed.This investigation was assisted financially by a grant from the Carnegie Institution of Washington.