Table of contents

A discussion is given of some factors which affect all microdensitometer studies on X-ray photographs. The particular problems which affect powder photographs, preferred orientation photographs, single crystal photographs and diffuse reflexion photographs are then considered. The use of a rotating circular stage for the investigation of rings of varying density and the use of an integrating mechanism for the determination of the integrated reflexion in a line or spot are described.

The construction and testing of a light scattering apparatus, suitable for the investigation of macromolecules in solution has been described. By the use of a parallel beam of light through the scattering solution, calibration anomalies have been removed and the apparatus can be calibrated by, or utilized for scattering measurements on, liquids of any refractive index.

Based on the principle of Lawaczeck's falling cylinder viscometer, a new viscometer has been designed, in which the only measurement to be made is the time taken by the cylinder to move a definite distance, without the necessity of either observing the movement of the cylinder or measuring the densities of the cylinder and of the liquid. The instrument consists of two exactly similar light solid cylinders or cylindrical bulbs moving in similar vertical tubes of slightly larger diameters containing the liquid at the same temperature. The ends of each cylinder are made conical to ensure its coaxial movement in the tube and the cylinders are attached to the ends of a Nylon fibre which passes over a light frictionless pulley. Attached to the same fibre at suitable heights above the cylinders are two similar light weight carriers on either of which riders of equal mass may be placed. When a certain number of riders are placed on one side, the cylinder on that side moves down while the other cylinder moves up with uniform speed, the pulley turning round once in a time T which is directly proportional to the viscosity of the liquid. This result may be used to compare the viscosities η₁ and η₂ of two liquids using the same number of riders and noting the times T₁ and T₂ respectively for a complete rotation of the pulley. η₁/η₂ = T₁/T₂.

The instrument is capable of high accuracy and has the special feature that a knowledge of the density of the liquid is not needed in the calculation of the result.

By arranging the strain gauges on a load cell as a closed bridge which is wired in parallel with a similar reference bridge in the measuring instrument, a very sensitive and accurate manually balanced null deflexion method of measuring the output of a load cell can be achieved at low cost. This method is also suggested as an alternative to the present d.c. methods used for load cell measurement in the calibration of testing machines.

The prototype bridge has a discrimination of one part in 10 000. A practical difficulty when used with load cells greater than 50 tons capacity is to calibrate against a standard of sufficiently high accuracy.

Double differentiation of the ion beam in a mass spectrometer is shown to have the same effect on peak shape as reduction to zero width of the inlet and exit shts. When this differentiation is performed by modulation of the accelerating voltage, increase of the modulating amplitude results in effective control of the width of both inlet and exit slits making the spectrometer more versatile since its sensitivity and resolving power are easily controlled. Differentiation by an odd number of times enables the centre of a singlet peak to be located with greater speed and accuracy, thus improving the mass measurements made with the spectrometer.

The seismograph described has a nearly uniform response to ground oscillations whose periods he between 1.5 s and 12 s, which is the range of particular interest for research on microscisms generated by sea waves. The seismograph consists of a 1 s pendulum which measures ground acceleration over the range of frequencies of interest, and an electronic circuit performing double integration to give a signal proportional to ground displacement. The 1 s pendulum has negative feedback which allows simple damping arrangements and easy absolute calibration, as well as improving stability and linearity. A horizontal-component instrument has been built, but the principle should be equally applicable to measuring the vertical component.

An instrument has been designed to measure the percentage of potassium in a 2.4 g sample of sodium chloride crystals in the range 0-4% with an accuracy of ±5%. A determination, which takes one minute, is made by recording photoelectrically the light scattered by suspended particles of potassium cobaltinitrite obtained by the addition of sodium cobaltinitrite solution to the dissolved sample The instrument, which includes a novel device for dispensing a fixed quantity of reagent, can be used to determine the percentage of other impurities in other substances by selecting suitable reagents.

Simultaneous measurement of electrolytic conductivity and magnetic susceptibility is achieved by observing the changes in output voltage of a transformer when its air core is filled with a specimen. Conductivity measurements for strong electrolytes have been obtained in which departures from accepted values are less than 0.07 mho m^-1 in the range 1 to 30 mho m^-1. The magnetic measurements generally have less precision, and errors of 2% occur for susceptibilities of the order of 10^-11 H/m.

From the several possible targets for the D(d, n)³He reaction the heavy-ice target proves to be the most suitable for outputs of about 10¹⁰ neutrons per second. Beam scanning in two perpendicular directions combined with rotation of the target is found to be necessary to secure a sufficient life of the ice surface.

A simple recording thermometer is described which is mains operated, has a total variation at less than 1% for a mains variation of 10% and a warm up time of less than 5 min. With the given constants full scale deflexion corresponds to 10° F. Any suitable 1 mA recorder may be used.