The measurements were carried out with an automated muti wavelength refractometer DSA-h between 17 January and 13 June 2013
Accrodin to the manufacturer's manual, the intrument can be used to measure the " refractive index of liquid media independent of opacity , viscocity and colour" The refractive index is determined via the measurement of the critical angle for total reflaction. to this end, the position of the dark line determined by means of a high resolution CCD linear array with 2048 elements.