The density of the aqueous solutions of the TX-100 and CTABmixture with ethanol was measured with a U-tube densitome-ter (DMA 5000 Anton Paar) at the constant temperature 293 K.The accuracy of the density measurements and the temperaturegiven by the manufacturer was equal to ±0.000001 g/cm3and±0.001 K, respectively. The standard uncertainty was equal to±0.0000017 g/cm3.