Photoacoustic spectra of As−S, As−Se glasses as well as the As₂(S,Se)₃ glasses have been investigated. Photoacoustic spectra of powdered samples give results comparable to those obtained from transmission spectra, the latter studies requiring preparation of thin films. Temperature-dependent studies of the As₂S₃ glass have been carried out. Optical behaviour of these glasses has been interpreted in terms of homoatomic bonding defects.

Quantitative estimation of coloured as well as colourless substances spotted on filter paper has been carried out by means of photoacoustic spectroscopy. The technique should be specially useful in the estimation of biological substances.

A simple gas-microphone photoacoustic cell is described in which there is no sizable loss of signal on opening the cell to the atmosphere or even under conditions of gas flow. Results obtained under different rates of flow of gases and chopping frequencies are reported. Except for carbon black, the photoacoustic signal is found to be independent of flow-rate for all the solid substances studied.