Patent GB-754142-A (GB)
Title: Improvements in and relating to an optical arrangement for recording the refractive index course in rotating centrifuge cells
IPC: G01N21/45
Filed: 1954-02-15
Abstract: 754,142. Refractometers. LKB-PRODUKTER FABRIKSAKTIEBOLAG. Feb. 15, 1954 [Jan. 4, 1953], No. 4399/54. Class 97 (1). Apparatus for measuring the refractive index at different points of a solution rotating in a centrifuge comprises an interferometric system including a beam-splitting foil in the plane of the axis of rotation of the centrifuge and cemented between the plane surfaces of two identical triangular prisms whereby two parallel spaced beams of monochromatic light are produced from a single incident beam and are directed to two diametrically opposite cells in the centrifuge, one containing the solution and the other the solvent; and optical means for examining the interference pattern produced by combination of the two beams. The apparatus may include an arrangement for indicating the derivative of' the gradient of the refractive index function of the solution. In the form shown, light from a monochromatic source A collimated by a lens El, is reflected by a prism F<SP>1</SP> on to the beam-splitting foil H cemented between identical prisms. G<SP>1</SP> and G<SP>2</SP>, which produces a transmitted beam reflected to a surface of a prism F<SP>2</SP> and a reflected beam directed parallel to the transmitted beam by the prism F<SP>1</SP>. The beams pass respectively through the cells M<SP>1</SP>, M<SP>2</SP> in the centrifuge L containing solution and solvent respectively and, passing through objective O<SP>1</SP>, O<SP>3</SP>, and O<SP>2</SP>, O<SP>4</SP> are reflected back to the cells by plane mirror P<SP>1</SP>, P<SP>2</SP>. The objectives O<SP>1</SP>, O<SP>3</SP> and O<SP>2</SP>, O<SP>4</SP> are respectively identical and are arranged with their adjacent focal planes coincident so as to form images of the mirrors P<SP>1</SP> and P<SP>2</SP> on the rear surfaces of their respective cells. The beams thus pass the cells again at the same radial position as at the first passage. The returning beams are combined by the foil H and directed by the prism F<SP>2</SP> and objectives E<SP>2</SP> and R to an observation position T where the interference fringes produced may be observed or recorded photographically. To ensure that each divided beam shall pass only through its appropriate cell as the centrifuge rotates an apertured disc rotated at the correct speed may be provided to obstruct the light paths in one position or, as shown in the Figure, polarizers J<SP>1</SP>, J<SP>2</SP> may be arranged before the two cells to give light plane polarized in perpendicular planes. Behind each cell is a second polarizer N<SP>1</SP> N<SP>2</SP> similarly arranged so that with the rotor in the position shown the beams may pass back through the cells but with the cells M<SP>1</SP>, M<SP>2</SP> interchanged the polarizers N<SP>1</SP>, N<SP>2</SP> respectively block the beams. Quartz plates Q<SP>1</SP>, Q<SP>2</SP> are arranged to rotate the planes of polarization of each beam through 45 degrees so as to allow interference. To enable a curve indicating the gradient of refractive index to be recorded simultaneously a diaphragm D<SP>1</SP> having a slit inclined to the gradient is placed before the light source and an image thereof is formed at D<SP>2</SP> where is located an edge, slit-shaped aperture or opaque bar inclined to the direction of the slit image or cylindrical lens S being provided to form in one direction an image of the edge D<SP>2</SP> and in the other an image of the cells M<SP>1</SP>, M<SP>2</SP> at the plane T. Alternatively an additional edge may be placed at the photographic plate T, the edge D<SP>2</SP> and plate being moved simultaneously at right-angles during exposure.