Trace Evidence Examination Questions and Answers

Answer: D

The Munsell chart is used to study the colour of soil.

The Munsell soil colour charts describe colour by hue, value (lightness) and chroma (intensity), with a notation such as 10YR 4/3. Forensic scientists compare questioned and known soil samples, dry and moist, against the charts so that colour is recorded in a standard way rather than by subjective names.

Density is measured with a density gradient column, refractive index of mineral grains under the microscope, and particle size by sieving or sedimentation. None uses the Munsell chart.

Answer: D

The statement that is not true is that an indirect physical match can be achieved even if external dimensions do not match.

An indirect physical match links two pieces of material that were once one by features continuing across the break, such as surface markings, grain, scratches and contours, even when the broken edges themselves cannot be fitted together. For such a match the pieces must still agree in their general characteristics, including external dimensions such as thickness and width; if those do not match, the pieces cannot have come from one object.

The other statements are true: larger pieces carry more features and so match more easily, damaged fracture surfaces force reliance on surface markings and contours, and any fit found is recorded photographically.

Answer: B

Herzberg's stain is used in the examination of fibre, chiefly the paper fibres of questioned documents.

Herzberg's stain is a zinc chloride-iodine reagent. It colours the fibres of a paper sample differently by their pulp: rag fibres (cotton, linen) stain wine-red, chemical wood pulp blue-violet, and mechanical (groundwood) pulp yellow. This helps establish whether two papers have the same fibre composition.

Saliva is examined for amylase and blood group substances, hair by microscopy of its scales, medulla and cortex, and vomit for food and poison content; none uses Herzberg's stain.

Answer: A

Fibres regenerated from natural proteins belong to the azlon group.

Azlon is the generic name for manufactured fibres made from regenerated proteins, such as casein from milk, zein from maize, soybean and groundnut protein. The protein is dissolved and extruded through a spinneret like other regenerated fibres.

Rayon is also regenerated but from cellulose, not protein. Sericin is the gummy protein that coats raw silk and is removed in degumming; it is not a fibre group. Synthetic fibres such as nylon and polyester are made from petrochemicals, not regenerated from natural material.

Answer: B

Glass strengthened by built-in stress is tempered glass.

The glass is heated close to its softening point and its surfaces are then cooled rapidly by air jets. The surfaces set first and are left in compression while the core is in tension, which makes the glass several times stronger. When it does break it shatters into small blunt cubes, which is useful when examining broken side and rear car windows.

Laminated glass is two sheets bonded to a plastic interlayer, as in windscreens, and cracks in a web without falling apart. Insulated glass is a double-glazed unit with a gap between panes. Neither is strengthened by thermal stress, and plasticized glass is not such a product.

Answer: D

Phthalocyanine is a pigment.

Copper phthalocyanine and its chlorinated forms are the most important blue and green organic pigments. They are insoluble, very stable to light and heat, and widely used in automotive and house paints, printing inks and plastics, so they are met often in forensic paint and ink comparison.

A solvent dissolves the binder and evaporates as the paint dries. A binder (such as an alkyd or acrylic resin) holds the pigment particles together and to the surface, and a lacquer is a type of finished coating. Phthalocyanine supplies colour, which is the role of a pigment.

Answer: A

Dacron is the trade name of polyethylene terephthalate (PET), spelt 'tetraphthalate' in the paper.

PET is the polyester made from ethylene glycol and terephthalic acid. DuPont sold the fibre as Dacron in the United States, and the same polymer is Terylene in Britain. It is the commonest synthetic fibre found in textile evidence.

Nylon 6,6 and nylon 6 are polyamides, not polyesters; nylon 6,6 was DuPont's earlier fibre sold simply as nylon. 'Dimethylene tetraphthalate' is not the polymer of any commercial fibre.

Answer: C

A club-shaped root is found in the telogen phase.

In telogen, the resting phase, growth has stopped and the root becomes a hard, bulb-like club with no surrounding tissue. Such hairs are shed naturally, so most hairs found at scenes are telogen hairs. Because the club has little or no nuclear material, they are poor sources of nuclear DNA.

Anagen (growing) hairs have a large, pigmented root often with a sheath of tissue and are typically pulled out by force. Catagen hairs are in transition, with an elongated, tapering root that is only beginning to form a club, so neither anagen nor catagen alone gives a fully clubbed root.

Answer: A

The standard is ASTM C 1084-10.

ASTM C1084 is the Standard Test Method for Portland-Cement Content of Hardened Hydraulic-Cement Concrete; the suffix 10 is the year of the edition. It estimates cement content from the soluble silica and calcium oxide of a crushed sample, and is used in disputes over whether concrete was made to specification, a matter of forensic engineering.

The other designations are different ASTM standards and do not cover the cement content of hardened concrete.

Answer: A

Both statements are correct, so the answer is Both Assertion and Reason are correct.

Rapid hardening cement, made with a higher tricalcium silicate content and finer grinding, gains strength faster than ordinary Portland cement. It is therefore used where early strength is needed, as in prefabricated concrete units and road works that must reopen quickly, which is what the Assertion, worded loosely, says.

The Reason states the defining property: at the same water-cement ratio and the same age, rapid hardening cement develops a higher strength than ordinary Portland cement, for example its 3-day strength is about that of OPC at 7 days. Neither statement is false, so the other options fail.