Patent GB-216026-A (GB)
Abstract: 216,026. Sadler, A. T., (Vernes, A., Bricq, R., Jobin, M. L. A., and Yvon, G. G. J.). Aug. 24, 1923. Comparison photometers.-The absorption and diffusion of light by a cloudy liquid, in order to estimate the quantity or the mass of the particles held in suspension in the liquid, is effected by an arrangement of apparatus on a common base plate 4; the apparatus utilizing two parts of a beam of 'light, one of which passes through, or is diffused by the liquid under test and the other part directed through a graduated wedge of neutral tinted glass. The two parts of the beam pass together by way of a photometric cube to the objective of a telescope, in the eyepiece of which they are simultaneously viewed. When testing for absorption the beam from the illuminant 3 passes through a collimating lens 5, part of the beam F' being directed by a pentagonal prism 6 to the receptacle 9 containing the material under test and the other part of the beam passing through a screen 32 of neutral glass of known opacity and a graduated wedge 18 to the pentagonal prism 16. This part of the beam then passes through a second wedge 17 to the photometric cube 15 having a central reflecting surface 2, Fig. 2. The first part of the beam is reflected to the cube 15 by a prism 10, passing through the transparent portions of the cube 15. From thence the two parts of the beam are received by the objective 24 of a telescope and are reflected to and imaged at the diaphragm 27 of the eye-piece. The amount of absorption is determined by the position of the wedge 17 which is adjusted until the images in the eyepiece 30 are equally illuminated. For the determination of the amount of diffusion of light by the substance under test, the receptacle 9 is rotated together with the prism 10 through 90‹, so that the reflected light from the substance is measured. In this arrangement a collimating lens 11 is moved into the position 11<1>. In order to provide for the alteration of the position of several of the elements involved in changing from absorption tests to diffusion tests by a single control knob, a disc 38 carrying the prism 10 and the receptacle 9 is mounted on an axle 39. A slot 40 engaging a pin 41 limits the movement of the disc, and a fork 42 in one with the disc 38 is arranged to engage a pin 47 on a pivoted arm carrying a collimating lens 11. The axle 39 also carries a member having three arms 43, 44, 45, one arm carrying the operating knob 46, the arm 44 the objective 35 and the arm 45 a pair of mirrors 36, 37. In the position of the disc 38 and member 43 shown the prism 10 and the receptacle 9 are arranged for absorption tests as in Fig. 3. Movement of the knob 46 brings the member 43 against the stop 8 and moves the disc 38 to the position for diffusion tests in which the receptacle 9 occupies the place of the prism and the lens 11 is brought into the path of the rays by the fork 42. In the position shown in Fig. 7 the apparatus is arranged for diffusion tests at angles other than 90‹. For this purpose the light is directed on to the two angularly disposed and parallel mirrors 36, 37. A modified form of the turntable arrangements is described in which springs and tappets are used to secure the disc 38 in the various positions required.