No description available.

No description available.

Methods are described for the analysis of the uranium and thorium contents of iron and stone meteorites. These elements are present in concentrations of about 10(^-s)gram per gram, and normally the quantity of meteorite available was limited (10 - 50 gram). Using the fluorimetric method for the microdetermination of uranium, 2 x 10(^-3)gram Uranium could be determined with an accuracy of 10%. Thorium estimates were accomplished by ɤ - particle scintillation counting of Thorium C in radioactive equilibrium with the thorium series; the counter had an extremely low background (about 0.9 counts oer hour). The Thorium C could be regenerated from the higher members of the thorium disintegration series and it could therefore be determined with an accuracy of 25%. A method was developed for the isolation of the uranium from meteorites using a retrograde solvent extraction technique involving nitric acid and diethyl other. Other chemical procedures evolved, permitted the analysis of both the uranium and thorium in single samples of meteorite. The techniques employed included solvent extractions, co-precipitations and a chromatographic separation of submierogram quantities of uranium and thorium was also accomplished by precipitating the latter element, with a sireonium carrier, using an organic precipitant. Methods for the removal of traces of uranium and thorium from reagents are also described. The determinations were correlated with the helium content of the meteorites to calculate their pre bable ages. The absolute amount of meteoritic helium, together with its isotopic analysis, enabled probable amounts of helium produced independently by cosmic rays and the naturally-occurring radio-elements to be estimated. Results suggest a probable age for eight meteorites of about 75 x 106 years, while six others appear to have solidified less than one million years ago.

The development of an apparatus for the measurement of amounts of helium in the range 10(^-5) to 10(^-8) is described. Studies were made of the previously unmeasured average fission neutron cross section for the reaction Fe(^56)(n, a)Cr(^53) and a value of 0.39 mb, obtained from irradiations in B. E. P. O. at Harwell and D. F.R. at Dounreay. The nuclear reactions Fe(^54)(n, p)Mn(^54) and Fe(^54) (n, a)Cr(^51) were also studied and values of the average cross section measured. The absolute fission yields of Mo(^99) and Ba(^140) in the thermal neutron fission of natural uranium were determined using helium analysis of an irradiated uranium solution containing boric acid to obtain the number of fission events. The chemical separation of the nuclides and the counting and standardization procedures are fully described. The results, of 5.94 and 5.87% for Mo(^99) and Ba(^140) respectively, and the errors involved are discussed in the light of previous values. The third section of the work was concerned with the calibration of photoneutron sources by destructive analysis of the beryllium cylinders for helium, also produced in the photo-reaction. A discussion of neutron source calibrations is included. The design, and experiments carried out with an apparatus which included a silver-palladium leak for hydrogen are described. Unfortunately this work was not completed, but suggestions are included for its conclusion.

Models for calculation of barriers to rotation from torsional mode frequencies were reviewed, and a new simple harmonic quantum mechanical treatment of two coaxial rotors with both internal and external barriers was developed. Torsional and librational mode frequencies of several sets of compounds containing hydrogenous rotor groups were obtained principally by incoherent inelastic neutron scattering, with reference to both new and old infrared and Raman studies. The internal and external potentials in the N(_2)H(_6)(^+2) halide salts were calculated using the new model. The external barriers were used to calculate the appreciable hydrogen bond strengths, and the internal barrier was found to be less than in ethane. The different phases of the monomethylammonium halide and PF(_6)(^-)salts were studied, including selective deuteration studies, and the new model again applied to obtain barriers. The model worked well for the chloride p-phase but began to break down for the bromide indicating loss of simple harmonic behaviour. The other phases all displayed non-harmonic behaviour. The internal barrier was found tobe intermediate between that of N(_2)H(_6)(^+2) and C(_2)H(_6). In the C(_6)H(_5)NH(_3)(^+)C1(^-) and Br(^-) salts the internal barrier was found to be very small, and the external -NH(_3)(^+) torsional barrier for the chloride was in good agreement with that in N(_2)H(_6)(^+2)C1(_2)(6-). A large number of methyl-halogeno compounds of the group IV elements were studied. Multiple top torsional mode frequency splittings were observed and their neutron scattering intensities related to their mode degeneracies. Several previous I.R. determinations were shown to be in error. The di-, tri- and tetra-methylammonium halide salts were studied and torsional mode splittings were again observed. Barriers to methyl rotation were found to be relatively high, and steric effects due to the short C-N bond length, and external influences, were found to be quite important.

Scanning Kelvin Nanoprobe (SKN) microscopy is a new technique, based on Lord Kelvin's theory of contact electrification, which is able to measure changes in the work function of a surface with nanometre- scale precision. This technique has great potential in the analysis of surface chemistry, especially that of self-assembled monolayers and biochemical interactions. This thesis examines the potential of SKN microscopy in analytical chemical applications. SKN microscopy is used and contrasted against a range of other analytical techniques, including atomic force microscopy (AFM), confocal Raman spectroscopy and common electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. A short background is given on SKN microscopy, as well as the other analytical techniques used. This is followed by a chapter discussing the theory behind basic electrochemistry and the electroanalytical techniques used in the thesis. Work is then presented on the hydrogen bonding environment in mixtures of dimethylsulfoxide (DMSO) in water. Confocal Raman spectroscopy showed that the hydrogen bonding environment in DMSO:water mixtures had a profound effect on the S-H (thiol) group of the amino acid cysteine, as well as on the thiol groups of the small-molecule protein analogue BMC. As molecular biologists use DMSO:water mixtures extensively in studies, this work brings up important issues concerning these experiments. SKN microscopy was used with a range of other analytical techniques including AFM, Raman spectroscopy and cyclic voltammetry to probe the formation and characteristics of a new derivative of phthalocyanine synthesised to avoid crystalline formation and to naturally form an amorphous thin-film. Films were deposited on a variety of substrates, including gold, high-order pyrolytic graphite and glassy carbon, and were compared with a range of other phthalocyanine compounds. Simple computer modelling was also carried out on the compound. The derivative was found to form nanoporous films which allowed the passage of positively-charged molecules less then 7Å in diameter. Self-assembling monolayers of organothiols on gold were then probed using the SKN and electrochemical impedance spectroscopy. Selections of linear, branched, cyclic, aromatic and biological organothiols were tested. The SKN was capable of directly measuring the length of a linear alkanethiol from the change in work function of the monolayer. The SKN also proved capable of measuring the degree of organisation of the monolayer - branched and cyclic alaknethiols, which are expected to form looser-packed layers, recorded more significant changes in work function. These results were confirmed by the use of electrochemical impedance spectroscopy to measure the effects of a monolayer on an electrode surface.

Chemical analysis is a continuous thread in the history of chemistry. This thesis, which concentrates on the period from the mid-eighteenth century until the time of the Alkali Acts of the 1860s, assesses the role of chemical analysis in terms of developing methodology, its adoption during what has become known as the industrial revolution, and especially its contextual setting within the early alkali and bleaching industries. The thesis traces the development of volumetric analysis from its early beginnings to the time when standard solutions became the accepted means of measuring an unknown component in the process of titrimetry. The research has focused on a range of industrial entrepreneurs (Lewis, Watt, Macintosh, Crum, Keir, Clark, Ure and Griffin) who pursued economic rewards by the application of chemical knowledge, and shows how their intuitive and innovative practical efforts created the means by which their chemically based processes could be controlled and nurtured by analytical means. Simple though some of these methods now seem, nevertheless they satisfied the technical and commercial needs of the period. One standard test, using indigo blue, has been shown to have developed into a routine method that allowed the growing demand for textiles to be met. The thesis concludes that industrial chemists and chemical consultants were successful in their analytical methods without depending upon a knowledge of atomic weights or chemical equations. The exploitation of simple measurements, and the quantitative relationships between reactants and the products of reactions, provided information and a set of technical resources sufficiently useful for the control and management of raw materials, purchasing, and quality control of saleable products.

No description available.

No description available.

In this work a novel micro-fading instrument has been developed that has increased structural stability, hence increasing the portability over previously reported instruments of this type. Using this instrument several new experimental methods have been developed and applied for the investigation of the photosensitivity of painted samples and coloured works of art (with particular focus on the effects of anoxic housing). The colour fading and reversion behaviour of a traditional Prussian blue pigment ground in gum Arabic was investigated for the first time in 0%, 2%, 3.5%, 5%, 10% or 21% oxygen concentrations. Results from this investigation indicated that the previously reported deleterious effects of reduced oxygen concentrations (hypoxia) for Prussian blue may only become relevant at oxygen lower levels (beginning at an hypoxic oxygen level above 2% and below 3.5%). An extension of the investigation to a large sample set of Prussian blues indicated that relatively low concentrations of oxygen (around 5%) may be tolerated by Prussian-blue containing works of art. The novel investigation of the effect of reduced oxygen housing using the microfading technique was extended to a very large varied sample set of traditional watercolour pigments ground in gum Arabic. This new avenue of investigation for the conservation of art work produced encouraging results to overcoming some of the problems of anoxic storage for a wider variety of watercolour pigments. This broad investigation also led to a better understanding of how much light exposure, in and out anoxia, is permissible for different types of watercolour pigments. Incorporating a linear variable filter into the design enabled the investigation of the wavelength dependence of fading of many samples to a greater degree of resolution than had previously been attempted. The wavelength dependence of fading for the samples tested was found to correlate well with the absorption spectra although an exception was found when testing a sample of Prussian blue pigment, where the degree of fading decreased with the wavelength of incident radiation.