Abstract
The value of pH measurement as a discriminatory technique for soils is investigated with particular reference to the development of a technique for the examination of very small samples. The variation of pH within five groups of soils of widely varying dry colours has been determined and found to be quite considerable, the distribution within each group being very similar. The discriminating power for the technique has been estimated to be approximately 0·4. Four colorimetric methods, based on BDH Soil Indicator, have been evaluated for their possible use in forensic science. A method in which a water to soil ratio of 2·5:1 v/w and a centrifuge for settling purposes were used was found to be the most satisfactory and capable of yielding reproducible pH values for samples varying from 2·5g to 50mg. A study of the effects of storage of a moist soil in a sealed polythene bag indicated no change in pH for up to fourteen days of storage.
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