K.W. Smalldon

The Calculation of Discriminating Power for a Series of Correlated Attributes

Procedures are described which enable the Discriminating Power to be calculated for a series of sample attributes. The conditions under which acceptable theoretical solutions can be obtained are illustrated and then a simple and completely general approach is described for any series of correlated attributes. The application of the concept of Discriminating Power is discussed as an aid to the solution of those management problems concerned with the choice of attributes which should be measured in order to maximize the average discrimination achieved on a long-term basis.

The transfer of fibres between clothing materials during simulated contacts and their persistence during wear. Part I--Fibre transference.

The persistence of wool and acrylic fibres has been studied on the surface of six representative articles of clothing during various periods of wear to a maximum of 34 hours. The initial rate of fibre decay was rapid for all the garments studied and the highest proportion of the original fibres which remained after 4 hours of wear was 18%. The rate of fibre decay was indistinguishable for wool and acrylic fibres on all garments studied. The three jackets and two sweaters despite the considerable differences in their construction and appearance, produced very similar rates of fibre decay. Fibres were lost at a significantly higher rate from a finely textured sports jacket and very rapidly from a cotton laboratory coat. In some of the experiments the length of fibres was recorded throughout, and the size distribution was found to be relatively constant during wear. This paper is intended to assist the forensic scientist with the interpretation of fibre evidence in those cases which involve fibre contacts, an area in which at present there is no documented knowledge. The possible mechanisms which could control fibre persistence on the surface of textile materials are briefly discussed.

The Transfer of Fibres Between Clothing Materials During Simulated Contacts and Their Persistence During Wear: Part III — A Preliminary Investigation of the Mechanisms Involved

A preliminary study has been performed to identify the mechanisms responsible for the transfer of fibres from knitted materials during clothing contacts and for their subsequent persistence on the surface of garments during wear. From the available data it is postulated that fibres are mechanically transferred by the following three processes. Some fibres already exist as fragments on the donor material and are exchanged during the contact ; a few fibres which are relatively loose in the yarn are pulled out ; and fibres are also produced by direct fragmentation occurring during the contact itself. The conditions under which a particular mechanism is likely to predominate are discussed. The results of the persistence study demonstrate that fibres remain on clothing during wear by means of mechanical interactions with the surface of the recipient garment. It is shown that the fibre persistence-versus-time curves can be well represented mathematically by assuming that fibres are lost by first order kinetic processes from three distinct states of mechanical binding. The different persistence-versus-time curves obtained for three particular garments are interpreted as meaning that the three states of binding are not similarly populated so far as these garments are concerned. The implications of the proposed mechanisms are also discussed in connection with some practical problems, such as the retrieval of fibres from the surface of clothing.

The Distribution of Glass Fragments in Front of a Broken Window and the Transfer of Fragments to Individuals Standing Nearby

Normal household windows of three different sizes were broken with bricks and hammers. Fragments of glass travelling in the opposite direction to the blow were in each case collected from the floor, which was covered with loose sheets of paper, up to a distance of 3 metres from the window. The number and size distribution of glass fragments falling on each sheet was determined. The amount of glass found per square metre decreased rapidly with distance in an approximately exponential manner and the rate of decrease was usually less rapid for glass fragments smaller than 1 millimetre than for larger fragments. This effect was particularly marked for the largest window. In the experiments subjects stood at various distances from the window and their clothing and hair were searched soon after the window had been smashed. Glass fragments were recovered in each experiment but very few of these were larger than 1 millimetre. The number of fragments smaller than 1 millimetre found on a subject was similar to the number found on 300cm 2 of floor-space near the subject. In most experiments at least one glass fragment was recovered from the hair by combing.

The quantitative multi-element analysis of human liver tissue by spark-source mass spectrometry

Abstract A procedure is described for the determination of 13 elements in human liver tissue by spark-source mass spectrometry. Spectral interferences are identified and calibration obtained by using carefully formulated synthetic standards. The relative standard deviation of this method is typically ± 9% for replicate analyses of a pooled liver ash obtained by oxygen plasma ashing, and ± 16% for replicate tissue samples taken through the whole analytical procedure. The accuracy of the method was checked by conducting complementary determinations by flame atomic absorption spectrometry. Results are presented for the multielement analysis of 15 livers by both methods and compared with literature values.

The Use of Spark Source Mass Spectrometry for the Analysis and Classification of Small Glass Fragments

Data accumulated from the multi-element analysis of milligram samples of various glasses are reviewed and a graphical procedure is described for the classification of modern window glass. The analytical method is extended to include samples weighing between 10μg and one milligram. The validity of the classification procedure is then checked for these small particles. Casework applications of the classification scheme are discussed.

The Determination of Iron and Magnesium in Small Glass Fragments using Flameless Atomic Absorption Spectrophotometry

A procedure is described for the determination of iron and magnesium in small glass fragments using flameless atomic absorption spectrophotometry. The fragments are digested under pressure in closed polytetrafluoroethylene vessels to ensure dissolution and avoid contamination. The precision for replicate determinations on 100μg fragments of modern window glass was ± 8% for iron and ± 11% for magnesium. When 100μg fragments of four standard glasses of widely different compositions were analysed good agreement was found between the known and experimental trace element concentrations. The value of the analysis to the forensic scientist, for identifying small particles of window glass, is emphasised.

The non-destructive analysis of single layered household paints using energy dispersive x-ray fluorescence spectrometry.

An evaluation of energy dispersive X-ray fluorescence spectrometry for the discrimination of single layered household paint flakes of similar colour is reported. Thirty paint samples, ten from each of the three colour groups red, green and white, were analysed under standard conditions. The reproducibility of the X-ray fluorescence spectra, for 2mm × 2mm flakes removed from different areas of a painted slide, has been investigated. Using 2mm × 2mm flakes discrimination of all the paints within the red and green colour groups was achieved. The white paint flakes were discriminated into nine groups. A combination of several other techniques could not achieve discrimination of all the samples. The spectra for all the paints examined are shown and the limitations of the method are discussed.

The Discriminating Power of Density and Refractive Index for Window Glass

The concept of discriminating power has been applied to the attributes density and refractive index for window glass. The discriminating power has been calculated at different error factors for the two attributes measured separately and then for both attributes combined. The results are discussed in terms of which attributes should be measured routinely for window glass.

The Comparison of Ink Dyestuffs using Minimal Quantities of Writing

A rapid thin layer chromatographic method is described for ink dyestuff comparisons which has been found useful, both in cases of document alteration, where only a few millimetres of pen stroke are available, and also where it is vital to cause minimal damage to a particular document.