GB446333A - Improvements in methods of photo-electrically measuring the light absorbing or reflecting capacity of substances - Google Patents

Abstract

446,333. Photometric apparatus. ZEISS, C., [Firm of], Carl-Zeiss-Strasse, Jena, Germany.-(Assignees of Papirindustriens Forskningsinstitutt; Sk÷yen, near Oslo, Norway) Nov. 28, 1935, No. 32986. Convention date, Dec. 15, 1934. Addition to 445,009. [Class 97 (i)] Apparatus for measuring the light-absorbing or the reflecting power of a substance comprises two photo-electric cells connected in parallel to each other and each connected in series to a resistance, one of the cells being alternately exposed to light transmitted or reflected by the substance under test and by a standard substance, and the other being illuminated by the light source. The ratio of the intensities of light incident on the first cell from the test material and the standard is obtained by comparing the fall of potential in one of the resistances or in a part thereof, with that in the other resistance or in a part thereof, the latter fall of potentital being so controlled by a graduated electrical control device that the two potential differences to be compared are equal. As shown, the cells A, B are connected to a source E of E.M.F. in parallel circuits including resistances 3, 4 in series with the respective cells. The resistances are provided with sliding contacts 5, 6, so as to be variable. Light from a source 7 illuminates a diffusing screen 13 from which light is directed to the cells A, B by tubes 9, 8. The tube 9 has a chamber 14 for a receptacle 15 containing the light-transmitting substance to be tested or a standard substance. With the standard substance in position and the contact 5 in its extreme position, the contact 6 is adjusted until. the galvanometer G reads zero. Then with the test substance in position the contact 5 is adjusted until the galvanometer again reads zero, the light-absorbing power of the substance being determined from the setting of the contact 5.