But the most important outcome of this work was that it became possible to use oil diffusion pumps for high vacua and to construct large high vacuum vessels in a demountable form. Oil diffusion pumps could create a high vacuum more readily than mercury pumps, and the use of Apiezon oils (making a liquid-air condensation trap unnecessary) enabled them to be built for the first time, thus leading to the present wide commercial range. Likewise Apiezon greases could be used to seal the joints in high vacuum apparatus, and devices that had previously to be sealed off could be continuously evacuated, for instance high power radio valves, x-ray tubes, and vacuum furnaces.

A manufacturing process for a high grade aluminium-silicon product known as M-V 'C' alloy was developed in the research department in 1927. This light alloy, which was due to A. Phillips, at that time the foundry metallurgist, and E. Baron, general foreman in the brass foundry, is exceptional in its ease of casting, ductility and strength, and resistance to corrosion. Originating in an agreement to reduce the weight of naval armaments, it is now used for many light castings, e.g. fishing floats.

Methods of working molybdenum and other refractory metals were developed to overcome the considerable difficulties in obtaining a supply of processed material. Sheet molybdenum was in great request for the anodes of radio receiving valves and other electronic devices.

The first laminated plastic of its kind, Traffolyte, was produced in 1927 for use in transformer nameplates. Before long it was being made as decorative panels and veneers, being particularly suitable for walls or fittings in kitchens, bathrooms, and restaurants on account of its stain-resisting qualities. During the last war it was widely used for its lightness and resistance to corrosion. The complete business was sold to De La Rue Insulation Ltd. of Newcastle in 1945.

As electrical equipment came into more general use, quietness of operation became important, alike in turbo-generators and watt-hour meters. Noise problems in engineering apparatus had been studied under Churcher for two years when in 1928 an acoustics laboratory was built. At first much time had to be given to designing and making accurate equipment for measuring and analysing noise, and many results of the fundamental investigations were subsequently adopted by the B.S.I, in their definition of the standard phon. Further work under A. J. King covered, among many subjects, the mechanism of noise transmission in ducts, which led to improvements in the noise-attenuating properties of ventilating systems and later enabled suitable testing structures for gas turbine plants to be designed.

TECHNICAL

The third decade was a period of far-reaching technical developments, both mechanical and electrical. In the power supply field the size of turbo-generator units jumped ahead, and a tendency towards higher steam conditions began to appear. The higher voltages in use overseas required new transformer and switchgear designs, which paved the way for the British 'grid'.