GB951473A - Differential refractometer - Google Patents

Abstract

951,473. Differential refractometers. J.L.L. WATERS. July 12,1961 [July 22, 1960], No. 25206/61. Heading G1A. A differential refractometer comprises a light source 10, Fig. 1, a refracting member 18 arranged to contain a reference liquid within a prism 24, and a surrounding sample liquid 28, the index of refraction of which is to be compared with that of the reference liquid, optical means 12, 14, 16, 30 arranged to pass a beam from the light source through the refracting member on to a beam bifurcating device 38, a detector arranged to receive the bifurcated beam portions on two separate sections 40, 42 of photo conductive light sensitive surface, possibly cadmium sulphide, having a sensitivity to radiation such that the resistance of each surface drops to less than 8 megohms when a square thereof, not greater than 3/64 inch on a side is illuminated by two foot candles, and operable means 44 for determining the relative magnitude of the beam portions received by the two photo sensitive sections. The means 44, may comprise an A. C. resistance bridge having the cadmium sulphide detectors in adjacent arms thereof, connected to an amplifier 46, feeding one phase of a two phase induction motor 48, mechanically connected to a rotatable glass block 34 laterally deflecting the beam of light to counteract any deflection of the beam by the refracting member, so that with the sample liquid in continuous flow through the refracting member the block 34 rotates, in response to the amplifier output so that the two detector portions receive equal parts of the light beam, the position of the motor rotor giving an indication of the sample liquid's refractive index on meter 52 and recorder 54. Alternatively, the motor, meter and recorder may be replaced by manual turning means and revolution counters respectively; The refractometer may be incorporated in continuous flow apparatus comprising a first block 58, Fig. 3, containing the light source and slits assembly, and the beam bifurcating mirror and detectors assembly mounted one above the other and a second block 60 housing the refracting member 18, mirror 30 and collimating lens 16, the two blocks, together with glass blocks 32, 34 and the induction motor 48 with its associated gearing, being mounted on a support 56, a third block 62 surrounding a steel pipe carrying the sample liquid up to the refracting member being carried under the support. All three blocks and support are of massive aluminium construction to minimise the effects of change in ambient temperature, a thermistor controlled heater also being included.