A method developed for the measurement of tissue blood flow is modified to measure the thermal conductivity of liquids and silica gels. The method controls a thermistor temperature at a set point above the baseline and determines conductivity from the power as a function of time. Natural convection in the liquids is suppressed by reducing the measurement time to 10 s and by reducing the temperature step, thus decreasing the magnitude of buoyancy. Conductivities were measured in six aqueous liquids and in gels constituted from these liquids with various amounts of silica. The technique determined the conductivity with a 95% confidence interval to less than 1% in nearly all cases. It was found that conductivity varied 0.3% per 1% silica for gels made from a CuSO4 solution and 1% per 1% silica for gels made from a Cu(BF4)(2) solution.