Patent GB-393648-A (GB)
Title: Improvements relating to the determination of quantitative characteristics of radiation
IPC: G01J3/40
Filed: 1931-12-10
Abstract: 393,648. Measuring light &c. radiation. HILGER, Ltd., A., TWYMAN, F., and SPENCER, L. J., 98, King's Road, Camden Town, London. Dec. 10, 1931, Nos. 34299/31 and 6631/32. [Class 97 (i).] Apparatus for the determination of quantitative characteristics of radiation comprises means for producing simultaneously a number of representations of the characteristic differing as to the quantity represented in predetermined steps of gradation, these representations being spaced apart so that a number of comparison representations of the characteristic in standard quantity can be placed between them. The invention is described principally in connection with a spectrophotometer for determining the absorption curves of liquids &c., and in this application it comprises means for simultaneously producing a number of spectra by light passing through successively increasing thicknesses of the medium, and for producing between these spectra a number of spectra all having the same intensity which lies between the maximum and the minimum of the firstmentioned series of spectra. The gradation is preferably produced by means of a wedgeshaped member which may be in the form of a cell, Figs. 1 and 2, consisting of two wedge-shaped pieces 1, 2 joined together, a groove 3 being ground through the piece 1 to provide a wedge-shaped receptacle for liquid. The front and rear faces are preferably formed as lens surfaces so that incident light is collimated by the entrance surface and then focused by the exit surface. The cell is used with a multiple-aperture diaphragm which may have two vertical rows of apertures 4, 5, Fig. 3, so arranged that the apertures in one row are opposite the bridges in the other. This diaphragm is mounted in front of the slit of a spectrograph &c. so that it can be shifted to bring either row of apertures into use, and two exposures are made, one through the cell and one row of apertures and the other through the other row of apertures, either direct or through the same cell containing a non-absorbing liquid. To avoid errors due to the fact that the light passing through any particular diaphragm aperture has traversed varying thicknesses of liquid, the liquid cell may be bounded by a surface of echelon form, Fig. 13, or the error can be minimized by locating the diaphragm on one internal face of the cell. The diaphragm is applied in the form of a coating of platinum on the bottom of the groove in the cell 1, a crenellated protector, Fig. 7, being first applied to the surface to protect from the platinum deposit the parts which are to become the diaphragm apertures. Another form of the apparatus is shown in plan in Fig. 16, in which the cell 19 is in the form of a rhomb having parallel vertical internally-reflecting faces 20, 21. The acute edge 22 nearest the slit 8 of the spectrograph is provided with a number of notches, Fig. 10. A second cell 34, containing a standard liquid, and similar to the cell 19 except that it has no notches, is mounted with the cell on a support 33 to which is fixed a condenser 26 to collimate the rays from the source, the arrangement being such that the light is divided between the rhombs 19, 34, the part incident on the face 20 being reflected to the edge 22 so that the rays incident on those portions of this edge which lie between the notches are again reflected and enter the slit 8. The rays incident at the centre of the face 36 of the rhomb 34 pass across to the centre of the face 37 and are reflected thereby so as to pass through the notches in the edge 22. The intensity of these rays may be reduced by means such as a rotating sector 30. Specifications 103,233 and 320,136, [both in Class 97 (i), Optical systems &c.], are referred to.