Some new developments in testing equipment for paints and inks

Optoacoustic spectroscopy is a completely new technique for the examination of solid and liquid samples and a system for this is now commercially available in the UK in the form of EDT's Model OAS 400 Opto‐Acoustic Spectrometer. This attrac‐tive instrument has been developed at EDT Research, 14 Trading Estate Road, London NW10 7LU, with the backing of the National Research Development Corporation from the pioneering work in the field by Dr G. F. Kirkbright of Imperial College, London. The principles of OAS rest on the fact that light absorbed by a solid sample is converted to heat with the sample. If the sample is sealed in a small cell containing a gas e.g. air or nitrogen the heat will be transferred to the gas and cause it to expand. If the incident light beam is now chopped at a steady rate, the gas in the cell will be alternately heated and cooled leading to a series of pressure pulses which can be detected by microphone. Scanning the wave‐length of the light and recording the associated sound amplitude leads to an absorption spectrum analogous to that of more conventional methods of spectrometry. The advantages of OAS lie in the fact that spectra of opaque substances, powders, polymers, suspensions and slurries can be made without difficulties arising from lack of transmission, scattering or reflection.