The photo-extinction method of fine particle size analysis by hydrophotometer is significantly faster and more precise than pipette analysis. Six samples are analyzed per hour by the hydrophotometer and calculations can be performed by computer in fifteen minutes. Hydrophotometer reproducibility, expressed as the standard deviation of phi percentiles of the cumulative curve is 0.11 Phi , whereas that of the pipette method is 0.45 Phi . Precision of both methods increases, in the course of analysis, from silt to clay; and the ranges of precision, respectively, are 0.07-0.36 Phi and 0.06-1.69 Phi . Sample treatment for hydrophotometer analysis is non-destructive (no sample drying) and great versatility in the nature of the settling medium and dispersant is afforded.

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