The particle size analysis of soils and its use in forensic science--the determination of particle size distributions within the silt and sand fractions.
Methods are described for the determination of the particle size distributions in small soil samples using a Coulter Counter Model ZB for the silt fraction (60μm–2μm) and conventional sieving for the sand fraction (2mm–60μm). An examination of the reproducibility of the methods using duplicate 1·5g samples of eighteen different soils has shown that they are highly reproducible and that the differences between the soils were easily demonstrated both in the silt and sand particle distributions. The methods have also been shown to be reproducible for sample weights as low as 200mg of whole soil.
A simple method for determining the pH of small soil samples and its use in forensic science.
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.
The wax fraction of soils: Separation and determination of some components
Resin- and asphalt-free wax components from a mineral soil and from a peat were separated into free acids, esterified acids and unsaponifiable material. The acids, as methyl esters, were fractionated by column chromatography on magnesium trisilicate to yield n-alkanoic- and hydroxy-acid fractions. The unsaponifiable material was fractionated on activated alumina, and fractions consisting of n-alkanes, n-alkan-2-ones (methylalketones) and primary n-alkanols were obtained. Gas chromatography was used to separate and determine individual components. The n-alkanoic acid fractions contained members with both odd and even numbers of carbon atoms ranging from C18 to C34 but with the latter predominating (80-90%). The carbon number of the n-alkanes and n-alkane-2-ones covered a similar range in which the odd-numbered members predominated (80-90%). The primary alcohols had a slightly lower average chain length (C16- C30) and 90% consisted of even-numbered members. These fractions together accounted for 25–30% of the resin- and asphalt-free wax.