The surface tension and density of octamethylcydotetrasiloxane and hexamethyldisilazane were measured between 25° and 45° C. The surface tension and density of solutions of hexamethyldisilazane-carbon tetrachloride, octamethylcydotetrasiloxanecarbon tetrachloride, and octamethylcydotetrosilaxane-n-hexadecane were measured at 30° C. All three solutions show deviations from ideal behavior. All the excess surface tensions are negative. The excess volume of the n-hexadecane solutions is positive, while the carbon tetrachloride solutions show negative excess volumes which change to positive values at high silicon compound mole fraction. The Gibbs surface excesses were calculated and are compared for the three solutions. © 1969, American Chemical Society. All rights reserved.