The Effect of Sedimentation upon Precipitation Kinetics SIR: A kinetic interpretation of precipitation reactions for very sparingly soluble salts is often atiiempted by use of the chronometric growth integrals developed by Nielsen ( 3 ) . The growth of precipitate particles is usually found to be surface-limited (so-called interfacecontrolled precipitation) and is a function of both the surface area of the growing cryrtallites and th,: supersaturation of t,he precipitating ioiis. Assumptions involved in this type of analysis are concerned with the stability, eccentricity, arid surface properties of the growing precipitate particles. Of practical and major importance in evaluating prccipitation rates is the simultaneous sedimentation of these suspended part.icles, a fact which has previously been ignored. The effects of sedimentation may be demonstrated by nephelometric data for typical precipitations ( 2 ) . Figure 1 shows the rise in turbidity as the heterophase grows and the subsequent decrease in turbidity as the particles sediment from solution. In these experiments, the growth of the precipitating particles is virtually complete before sedimentation occurs because the particles formed are small (generally
