Extensive measurements have been made, at ten megacycles, of the temperature dependence of ultrasonic velocity in liquids and liquid mixtures. All single liquids tested, except water, were found to have large negative temperature‐coefficients in the temperature range of zero to 80°C. Water has a large positive coefficient at room temperature, decreasing to zero at 74°C and then becoming negative (with a peak velocity of 1557 meters/sec.). Solutions in water of various other liquids (and of some solids) give parabolic velocityvs.temperature curves like that for water but with the peak velocity and peak temperature values shifting with the concentration of the solution. In general increasing the concentration raises the peak velocity slightly and lowers the peak temperature markedly from the values for water alone. It has also been found possible by compounding three‐component solutions to adjust the values of the peak velocity and peak temperature independently within a narrow range of velocities and a wide range of temperatures.