Table of contents

The conversion of a 40 Mc/s Varian nuclear magnetic resonance spectrometer to 80 Mc/s operation is described. The increase in maximum field strength from 12 to 22.5 kG was achieved by the use of conical Permendur pole caps. The factors affecting pole-cap geometry are discussed. Sufficient field homogeneity for the production of high resolution 80 Mc/s hydrogen nuclear magnetic resonance spectra was achieved with Golay electric shim coils. Further stability of the magnetic field, enabling spectra to be recorded on precalibrated chart paper, was achieved by a double audio-frequency modulation technique. Notes are also given on the associated changes required to the electronic circuits.

The essential features of the construction of a nuclear-electron double resonance spectrometer are described. Both a helix and a resonant cavity have been used as the microwave resonators and the performances of both probe systems are compared. An example of the performance is given.

A description is given of the design and performance of a manometer comprising an inclined sight tube and a movable reservoir, in which the need for a flexible connecting tube is avoided by tilting the whole liquid container about an axis nearly coincident with the centre line of the sight tube, with simple mechanical compensation for `cosine error'. The combined scatter in a calibration against a Chattock gauge was generally within ±0.0001 in. of liquid (±0.2 mtorr), the time lag and zero drift are much less than those of a Chattock gauge, the linear dimensions are about half those of a Chattock gauge of similar range, and the instrument can withstand large overloads with no change of zero reading.

Constants have been measured for the Philips EM200 which enable the total current striking the specimen to be determined from a single reading of the exposure meter. In addition an approximate measure of the distribution of electrons striking the photographic plate can be obtained simply by photographically recording an image of the beam and measuring the radius of the blackened area. Together with the exposure meter reading this is sufficient to give the approximate Gaussian distribution at the photographic plate. It is related to the distribution at the specimen level by assuming that electrons are lost from the beam by collision with molecules of the residual gas.

Three methods of using a four-circle x-ray diffractometer are described. According to method No 1 the crystal is orientated with one given crystallographic axis parallel to the phi axis of the instrument and a reciprocal axis normal to the first axis is set perpendicular to the χ and phi axes. The cell dimensions must be accurately known. According to method No 2 the crystal is set up with an arbitrary unknown orientation which is found by measurement on the diffractometer. The cell dimensions must be known as in method No 1. According to method No 3 the crystal is set up with an arbitrary unknown orientation and the cell dimensions need not be known at all. Both the orientation and the cell dimensions are found in the course of the work.

Modifications are described which enable a commercially available British mass spectrometer to measure small differences in oxygen and carbon isotope ratios with a precision of ±0.01% and using as little as 0.1 ml. carbon dioxide sample. This precision is needed for geological work but might also find application in the use of stable isotopes of oxygen, nitrogen or carbon as tracers in biological systems, where substantial isotopic enrichment could be detected in samples as small as 0.001 ml. It is shown that a viscous inlet system is not a necessary requirement for precise isotope ratio work.

A potentiometric method for determinations of hydrogen in inert gas mixtures is proposed which makes use of a cell involving porous graphite electrodes activated with a thin layer of platinum-black catalyst. These electrodes are similar to the high-performance ones used for fuel cells, and the equilibrium is rapidly reached and maintained. This method results in an accuracy to better than ±0.2% and is applicable for continuous determinations of hydrogen varying from 100 to 0.1% in the inert gas mixture.

A modification to the Sawyer and Tower circuit is proposed which removes two of the major drawbacks inherent in the original, namely the introduction of phase differences between the voltages on the X and Y plates of the oscilloscope arising because of the different circuit components used in the two branches and also because of the finite conductivity of the sample under investigation.

A wavelength-independent, direct-reading radiometer has been developed to facilitate radiant power measurements in the near ultra-violet, visible and infra-red range. The sensor probe of the radiometer is designed to convert all incident radiant energy into heat, thereby providing a wavelength-independent method of light measurement. The amount of heat developed is measured with a specially designed `black-body' thermistor bolometer. The bolometer probe dimensions are less than 1 cm × 1 cm × 4 cm so that radiant power measurements can be made in confined areas. The instrument provides direct read-out of incident radiant power in units such as mw cm^-2 or erg cm^-2 sec^-1. The instrument can be used over the range from less than 10^-4 w cm^-2 to more than 0.25 w cm^-2. Depending on the type of window material used in the probe, the radiometer can provide wavelength-independent measurements from 250 nm to more than 40 μm.

A semi-absolute method for thermal conductivity measurements on solids near room temperature is described. Heat from a heat source flows through a sample of uniform cross section to a heat sink which transfers this heat by thermal radiation to the surrounding chamber walls. The temperature T₀ of the chamber walls and the temperature T₁ of the heat source are kept at constant levels with T₁ > T₀. At temperature steady state the measurement of T₀, T₁ and T_x (heat sink) allows the calculation of the thermal conductivity if the emissivity of the heat sink is known. The emissivity is determined with standardized specimens. Details of an apparatus utilizing the described method are given. The method is accurate to 3-5%, even for samples with a side as small as 2-3 mm.

A liquid-air cryostat, based upon the Wessell system, is described, together with a thermoregulator employing a copper resistance coil as a sensing element. The thermoregulator responds in a linear manner in the range +20 to -187°c and will control the preset temperature to within ±0.1 degC.

The instrument described was designed to measure the temperatures at which phase separations occur, particularly the cloud points of solutions containing surfactants where high optical density makes visual estimations impracticable. The principle upon which the apparatus is based is that of the change in the ratio of the scattered to transmitted light when a liquid system ceases to be homogeneous. This is detected by means of a photoconductor bridge operating a simple servo mechanism.

The construction is described of a high temperature (3000°C) graphite resistance furnace incorporating two new features. These are the use of a graphite guard-tube to facilitate easy replacement or renewal of the element and the use of carbon felt and carbon wool as a thermal insulator in place of carbon black. The assembly is simple to operate and can be constructed easily and relatively inexpensively.

This note describes a stirrer arrangement which was found to overcome the problem of the settling-out of particles when a Coulter counter is used for size analyses of particles which are coarse or dense.

A novel design of split mould is described which overcomes the contraction problem and has been found to be very convenient for growing metal single crystals of regular cross section using a horizontal travelling furnace.

A simple lapping device is described with which long thin rods of rectangular cross section or flat plates (⩾ 0.5 mm thick) of very brittle materials can successfully be prepared.

The use of tapered-gasket support in a stepped-piston device enables pressures of 50 kb, combined with high temperatures, to be reached at lower press load than in designs hitherto. The influence of sample length on load distribution has been studied.

A specimen cartridge, which holds the electron microscope grid with its normal inclined at 60° to the beam, has been constructed to facilitate the crystallographic examination of textures and the exploration of the reciprocal lattice of crystalline specimens.

The details of construction of a simple, non-electrical, liquid nitrogen level controller are presented. The level controller maintains the liquid nitrogen level in a vacuum cold trap sufficiently constant for the attainment and maintenance of pressures less than 0.1 ntorr for prolonged periods.

The adaptation of an American technique for use with a British liquid epoxy resin and exotherm inhibitor is described. This results in superior castings compared with those usually obtained using the popular solid epoxy resins. Typical properties of the cured resin are given.

An inexpensive fraction collector which uses continuous rather than intermittent rotation is described. Samples of constant volume are collected from a freely swinging funnel which is tripped at intervals by the lips of the sloped collecting tubes. Avoidance of intermittent rotation makes it possible to eliminate electrical contacts and electronic devices, with resultant greater reliability.

The amount of aluminium which can be evaporated from a graphite crucible is greatly increased if silicon is first evaporated. A small low-power aluminium source is described which utilizes this fact. So far more than 2.5 g of aluminium have been evaporated without apparent damage to the source.

An instrument for making glass microelectrodes is described. The glass is drawn in two stages, the first pull by gravity, the second by an air cylinder. Use of an air cylinder allows the instrument to be more compact and simple than the previous ones, while equally versatile.

This note describes a valve which forms a connection for re-pumping and sealing off the vacuum space in metal cryostats and similar equipment and also acts as a safety valve. The part that is permanently fastened to the cryostat is designed for cheap and easy quantity production, and the attachment by which it is operated can be shared between many pieces of equipment.

Two simple circuits are described which, respectively, enable many screw type tensile testers to be operated under constant strain rate or constant stress conditions.

A recording optical extensometer, which enables the adsorption expansion of solid blocks of coal to be measured over extended periods, is described.

Comments are given on methods of producing high-frequency modulated light by the use of moving mirrors or electronic techniques.