Table of contents

An account is given of a suspended-solids recorder which makes use of the principle of measuring continuously the ratio of the light transmitted by a water sample to that scattered from a beam passing through it, using a single photocell and amplifier. Two light beams, passing at right angles through the sample, are chopped at characteristic frequencies so that the component of photocell output due to transmission may later be separated from that due to scatter. The range of the instrument can be varied between 0-20 parts per million and 0-1000 parts per million. Readings are not affected by variations in incident light, sensitivity of amplifier or photocell, fouling of cell windows, colour of suspended particles or dissolved colour.

An expression is derived for magnetic fields with axial symmetry relating the actual value of the flux density at a point on the axis to the flux density measured by a search coil. It is shown that the error due to the search coil depends upon the even order derivatives of the actual flux distribution, and in some cases may be eliminated by careful design of the coil.

A scaling circuit is described which has proved extremely reliable, consisting of two dekatron stages followed by a mechanical register. The resolving time of the circuit is 250 μsec.

An apparatus is described in which a simplified calorimetric method was used for the measurement of energy losses in small samples of soft magnetic materials, which were subjected to alternating magnetization in the region of high flux densities and low audio frequencies. Measurements were made near the centres of single strip specimens used on open magnetic circuit. The method of measurement is without frequency or waveform limitations.

An apparatus for the determination, near room temperature, of the Seebeck coefficient at a point on the surface of a semiconductor is described. Measurements are simplified by the use of a direct reading potentiometer circuit, and the design of the sample mounting permits rapid measurement at a large number of points.

The mounting has a damped section for suppressing resonance and an undamped section for attenuating high frequencies. To isolate horizontal vibrations, the platform either hangs by fine wires or rests on thick bi-spherical lenses.

Signals produced by the current in a Langmuir probe circuit have, when modified by a simple differentiating network, been used to obtain electron energy distribution characteristics. Tuned filters are essential for the elimination of spurious signals, and their required properties are discussed.

A specimen holder is described which allows the specimen to be rotated through 360° about its own axis of symmetry. This adjustment is provided both before and after two curved slides whose axes of curvature are mutually orthogonal and orthogonal to the 360° rotation axis. Each curved slide allows a variation in orientation of the specimen of ±15°. This specimen holder can be fitted to the Leitz Ultramicrotome with only slight modifications to the advance arm and the removal of a small amount of material from the binocular mounting and main casting. The development of an X-ray Laue back-reflection camera to enable the orientable holder to be employed to orient given crystallographic planes into the plane of cutting is described.

A conventional vacuum system has been modified to enable an ultra-high vacuum to be obtained in a large volume. A liquid nitrogen trap, situated part way up a tall glass vacuum vessel, isolates the working space from the rest of the system. Thus, the trap and the working space being seal free may be baked at 425° C. The rest of the system uses demountable indium metal seals and is exhausted by a 9 in. oil diffusion pump with a refrigerated chevron baffle. Baking the vacuum vessel enables a pressure of 1.5 × 10^-8 torr to be obtained rapidly. With liquid nitrogen circulating and titanium getters fired, an ultimate of 1.5 × 10^-9 torr is readily achieved.