Dilute Triton X-100 in water as a reference liquid for hydrometer calibration using Cuckow’s method

•New fluid for use as reference liquid for hydrometer calibration using Cuckow’s method.•Advantages over traditional hydrocarbon fluids such as nonane and tridecane.•Safer and less expensive.•Density can be determined with sufficient accuracy from the mixing ratio.

We propose a 200 parts in 106 by volume solution of the surfactant Triton X-100 in water as a reference liquid for hydrometer calibration using Cuckow’s method. This liquid has advantages over traditional hydrocarbon fluids such as nonane and tridecane; it is safer, less expensive, and the density can be determined with sufficient accuracy from the mixing ratio. Previous researchers have used about 70 parts in 106 by volume Triton X-100 in water. Here we report measurements on the surface tension behaviour of aqueous Triton X-100 solutions with concentrations in the range (39–301) parts in 106 by volume. These measurements indicate that a 200 parts in 106 mixture is a suitable compromise between surface tension behaviour and accuracy of calculation of the liquid density from the mixing ratio of Triton X-100 to water. Performance tests to confirm the suitability of this liquid are given.