Abstract: A method for the measurement of the concentration of a material such as dextran or raffinose in a solution, notably a sugar solution, includes the steps of measurement of the optical rotation of a solution sample, treatment of the sample with a reactive agent, measurement of the optical rotation of the sample after treatment to ascertain the difference that said treatment has made, and calculation of the concentration of the material by reference of said difference to a suitable standard. The reactive agent reacts with the material sufficiently to alter the optical rotation of the sample.

Abstract: A method of calibrating polarimeter to work at an unknown wavelength comprising calibrating the polarimeter at a standard wavelength, using the calibrated polarimeter to measure a sample, measuring the same sample at the unknown wavelength and setting the polarimeter to give the same measurement at the said unknown wavelength as at the known wavelength. The method is particularly applicable to be calibration of a saccharimeter to work at an unknown wavelength in the near infra-red for the measurement of dark sugar samples. The invention is also a polarimeter or saccharimeter for carrying out the method.