A LINEAR DIFFERENTIATING REFRACTOMETER

A new version of the linear critical-angle refractometer for liquids i s described: a 1728 element linear CCD array is used to scan the inten sity profile of the output image, within which the position of a cut-o ff edge is a linear function of refractive index. The precision in loc ating this cut-off edge is greatly increased, especially for milky liq uids, by differentiating the intensity profile numerically. Further in formation about complex particulate liquids is found to be given by th e shape of the differentiated profile, and alternative internal and ex ternal illumination modes are provided which may give more information ; the interpretation will be discussed in a later paper. The present i nstrument covers the refractive index range 1.3000 to 1.4700, with an accuracy of +/- 0.0001 for transparent liquids. The light source is an LED at 635 nm. The intensity profile, the differentiated intensity pr ofile, and the refractive index value are all computed, displayed and printed by a desk-top computer.