Innovations in gold extraction
- Authors: Davidson, Raymond John
- Date: 1993
- Subjects: Gold -- Analysis -- Research Gold -- Metallurgy -- Research Gold mines and mining -- Research
- Language: English
- Type: Thesis , Doctoral , DSc
- Identifier: vital:4317 , http://hdl.handle.net/10962/d1004975
- Description: The thesis takes the form of a collection of publications and patents concerning gold extraction which were presented over a period of 18 years while employed at the Anglo American Research Laboratories.
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- Date Issued: 1993
The effect of ultraviolet and gamma irradation on soluble calf-skin collagen
- Authors: Davidson, Raymond John
- Date: 1967
- Subjects: Collagen -- Hide powder Irradiation Solids -- Effect of radiation on Gamma rays -- Dose-response relationship
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4290 , http://hdl.handle.net/10962/d1003718
- Description: Initially the present study was confined to the effects of ultraviolet irradiation on acid-soluble collagen. Such a study was undertaken in order to demonstrate the critical role played by tyrosine and phenylalanine in the intermolecular interaction of the telopeptides protruding from the rigid parent collagen molecule. Since both tyrosine and phenylalanine are photosensitive, and because the collagen telopeptides are relatively rich in these aromatic amino acids, carefully controlled degradation studies involving telopeptide liberation could be made. It became increasingly apparent during the course of investigation, that a better understanding of the subunit composition of thermally denatured acid-soluble collagen was necessary if a satisfactory interpretation of the irradiation studies was to be made. A subsequent study of the subunit composition of thermally denatured acid-soluble collagen resulted in the isolation and characterisation of two major and two minor dimeric components as well as the α- and β - subunits. Three acidic telopeptides and three basic telopeptides were also isolated from acid-soluble collagen during the course of the present study. The presence of the dimeric components while related directly to the method of preparation, suggested that acid-soluble collagen was largely dimeric in nature. Such a conclusion suggested an intermolecular rather than an intraolecular relationship between neutral-salt-soluble and acid-soluble collagen. While it is currently accepted that an intramolecular relationship exists between neutral-salt-soluble and acid-soluble collagen, such a relationship does not satisfactorily explain the very different solubility characteristics displayed by these soluble collagen extracts. With this in mind, and using the study on the subunit composition of thermally denatured acid-soluble collagen as a basis for comparison, the intra and intermolecular relationship between neutral-salt-soluble and acid-soluble collagen was investigated using ultraviolet and gamma irradiation. The effects of ultraviolet and gamma irradiation on soluble collagen preparations proved very similar. Although collagen samples were irradiated in solution from an ultraviolet source; and under anhydrous conditions from a gamma source, much the same degradation mechanism resulted. The initial depolymerisation of dimeric material followed by peptide fission, yielding irradiation-resistant crystalline portions of the parent triple helix, took place in both instances. At the same time, both studies indicated no significant differences in the intra or intermolecular structures of the neutral-salt-soluble and acid-soluble preparations investigated. The dimer content of neutral-salt-soluble collagen preparations was, however, noted to be smaller. To current methods for the preparation of soluble collagens, it may be concluded that such preparations are peptideless to some degree. While the native tropocollagen monomer with its full complement of telopeptide side chains may actively undergo linear polymerisation resulting in fibre formation, the soluble collagen preparations referred to above may only aggregate in a rather random fashion.
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- Date Issued: 1967
A critical study of the curcumin method for the determination of boron in plant material
- Authors: Davidson, Raymond John
- Date: 1958
- Subjects: Plants -- Nutrition , Boron , Turmeric
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4458 , http://hdl.handle.net/10962/d1011003
- Description: Methods for the determination of boron are reviewed. A thorough investigation of the curcumin method was undertaken. Factors such as spectral absorption, boron volatilisation and the effects of pH, the stability of reagents and colour solutions, the drying of reaction products and the interference from certain elements, were investigated. A study of the efficiency of extracting boron from plant material using an ashing procedure is presented. The modified curcumin method for the determination of boron in plant material is described. The statistical accuracy and precision of the modified method is presented. The modified method was used to determine the boron content in citrus and pineapple leaf samples obtained from various parts of the Eastern Cape.
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- Date Issued: 1958