Patent GB-550932-A (GB)
Title: Improvements in photometers
IPC: G01J3/40
Filed: 1941-07-28
Abstract: 550,932. Photometers. INSTITUTE OF PAPER CHEMISTRY. July 28, 1941, No. 9571. Convention date, Aug. 3, 1940. [Class 97 (i)] In a photometer capable of - use with a spectrograph, light from a standard and from a test sample is passed in alternation along the optical axis and means is moved across the axis, in phase with such alternation, dividing the beams into bands, the bands from the test sample being of graduated light energy and interdigitated with those, of uniform energy, from the standard. As shown, the photometer comprises a shaft 35 driven by a motor 40 and carying a flywheel shutter 46, a sector disc 66, and eccentrics 65, 90, 97, respectively causing a grating 51, cells carrying standard and test liquids, and a vibration-compensating frame 93, to oscillate across a collineated lightbeam 27 passing to a spectrograph 26. The shutter 46 has two diametrically arranged sectorshaped apertures extending over 110 degrees each, and the disc 66 has a sector-shaped aperture 67, Fig. 5, of 100 degrees, diametrically opposite an aperture 70 having an angular extent which increases, in steps of 10 degrees each, from 5 degrees near the shaft to 100 degrees at the circumference; the apertures of the shutter 46 and disc 66 are in phase. The grating 51 has interdigitated rods 57, Fig. 7, extending from opposite sides of, and partially across, a vertically-extending aperture 53, so as to form two series of aperture-bands ; it is carried by two spring steel reeds 60 secured at their bottom ends and engaging opposite sides of the eccentric 65. The liquid-carrying cells 72, 73, Fig. 3, are formed of fused quartz, and are carried by spring steel reeds 80 engaging opposite sides of the eccentric 90 ; the eccentrics 65, 90 are in phase and so arranged that the beam alternately passes through one cell and the other apertures, the change-over periods being masked by the shutter 46. The frame 93 is empty is mounted similarly to the grating 51, and the eccentric 97 is 180 degrees out of phase with the other eccentrics to cause the rocking of the frame to compensate for vibration. The speed of the shaft is such as to cause a large number of alternations during one exposure, and the film in the spectrograph may exhibit spectral lines L<SP>1</SP>, Fig. 11, divided into parts A of uniform intensity, produced by light passing through the standard, and parts B of graduated intensity produced by light from the test solution ; comparison of the parts A and B enables transmittance data for each spectral to be determined. The cells 72, 73 may be removed and replaced by optical filters, or by a sample 153, Fig. 17, of paper to be compared with a standard 154 for reflected light ; the sample and standard are mounted on the shutter 46 and lighted by a source 155 and condenser 157. For spectral comparison of two light sources, prisms 167, 170, Fig. 20, may be used in a cage 166 replacing the cells 72, 73, the light sources being oppositely laterally displaced from the optical axis, and their beams being alternatively refracted into the axis by the prisms as they cross the axis. A construction is described in which the liquid cells are in a rotating carrier secured to the shaft 35; centrifugal action causes suspended particles, bubbles, &c. to be thrown out of the beam. Modifications of the disc 66 are also described in which the stepped edges of the aperture 70 are replaced by a radial edge and by a curved edge, or the apertures are 'formed by arcuate slots of appropriate positions and lengths.