PREVIOUS measurements of the heat produced by ultrasonic waves in a trap vessel1 gave results that differed from those obtained by other methods2 for the absorption coefficients in carbon disulphide, xylene and kerosene, the last two appear to have abnormally high values, particularly from measurements with narrow trap vessels. The results were confirmed with trap vessels made of plaster of Paris, with windows of thin paper or ‘Cellophane’ in place of mica. The abnormal behaviour cannot, therefore, be attributed to any electrical effect in the metallic core of the trap, or to the mica windows.