A new optical method of continuously analysing the surface properties of a single pendant drop while obtaining quality bulk spectral and refractive index measurements of the liquid-under-test

The classical stalagmometer has been replaced by the tensiometer to measure surface properties from drop volume. From the drop period T₁, converted into volume, the surface properties of the liquid can be obtained. In the fibre drop analyser the use of the graphical signal (tensiotrace), significantly extends the measurement potential of the tensiometer by providing additional measurands. This instrument produces a series of peaks. The third-order reflection is known as 'the tensiopeak-period' t₃, and accurately predicts the value of the drop period. The results of an experimental study confirm the relationship between T₁ and t₃ for a wide range of liquids and are supported by ray-tracing modeling. Very sensitive and high quality bulk UV-visible spectra and refractive index measurements can be obtained from the drop-under-test.