Table of contents

The maximum temperature which can be attained by an electric furnace is usually limited by the refractories used to support the metallic winding This limitation has been overcome in the furnaces described by suspending the heating element inside the refractories thus permitting temperatures to be reached in excess of those otherwise obtainable - up to 2300° C with a powerinput of 40 kW. Two of the furnaces have a tungsten wire element, whilst the third is a simple graphite-tube furnace designed for easy operation.

A Debye-Scherrer camera has been designed to accommodate apparatus for maintaining the specimen at high or low temperatures. The specimen holder is at all times accessible, and the film holder is detachable. An apparatus has been devised for accurately controlling the temperature of the specimen between room temperature and -110° C. The specimen is enclosed in a chamber of still air, cooled externally by boiled liquid oxygen conducted between a succession of concentric cellophane windows. Special provision is made to prevent deposition of ice. Lattice spacing measurements of aluminium at temperatures down to -97.5° C. are in agreement with those calculated from the coefficient of expansion of the bulk metal.

A multi-stud potentiometer and fine wire wound rheostat combination giving a potentiometer ratio which is an exponential function of the dial settings, is described.

The potentiometer has been used successfully in a radar time base in which it constituted one arm of a bridge circuit. The accuracy was one part in 4000 using individual resistors having a tolerance of ± 0.1%. In the application mentioned the two dials were ganged and the range setting was indicated on a counter.

A new method for mutual conductance measurements is described. The valve under test is connected as a cathodeloaded grounded-grid triode and a known alternating voltage in series with a current indicator is applied across the load. Since the current through the meter is shown to be nearly proportional to the dynamic mutual conductance the instrument can be directly calibrated in terms of this quantity.

Barrier-layer photocells have many attractive properties which make them useful for the measurement of high temperature, and several papers.published in the last few years form the basis of the application of these photocells in reliable industrial pyrometers. This note is on the design of these pyrometers, and nomograms are reproduced which simplify the calculation necessary in the design.

A geometrical construction is given for determining the position of the image formed by a spherical mirror. The construction is used to develop algebraic expressions for the longitudinal spherical aberration, and the sine condition error, of a spherical mirror enabling rapid calculations to be made.

An apparatus is described by means of which small individual drops of accurately known uniform size may be produced. The drops are formed at the tip of a hypodermic needle round which is flowing a concentric stream of air. By varying the speed of the air, the size of the drops delivered from the microburette can be varied over a wide range.

After referring to difficulties encountered when using standard conductivity cells, a brief reference is made to that part of the author's previous work on the measurement of electrolytic resistance which is essential to the present paper. Two new radio-frequency current arrangements for titration are described in both of which a length of Pyrex glass tube fitted with external electrodes displaces the usual type of conductivity cell. The attendant difficulties of the latter are thus avoided.

The solution under analysis is drawn into the Pyrex tube where its resistance is measured (a) by its effect upon the Q of the oscillator, and (b) by its resistance to radio-frequency currents which are rectified and then measured by a zero-shunted microammeter.

A syringe is employed to draw the solution into the Pyrex tube. The use of a variable coupling condenser is suggested when making microammeter settings before titrating.

An easily assembled micro-apparatus for electrophoresis is described together with its auxiliary equipment. The apparatus combines the refinements of previous cells of rectangular cross-section with a simpler construction, from general laboratory materials, and the novel feature of reasonably accurate temperature control by means of a specially designed thermostat fitting on to a microscope stage. The arrangements for the application and measurement of a variable potential gradient are indicated. Microscopic observation of the dispersed particles is facilitated by means of dark-field illumination. A brief account is given of the theory underlying the method together with representative results. The latter are in good agreement with theoretical requirements and also with comparable data obtained by a macroscopic, moving boundary method.

The paper describes an adjustable horizontal worktable which provides a vertical movement to the upper surface without impairing the parallelism of the upper surface to the base.