The Fototurbidimeter in the Determination of Water Turbidity

Abstract

Notwithstanding our interest in the new methods which have been proposed till now, we still know of none which can replace it advantageously. The apparatus and method have been officially adopted by the Laboratorio de Obras Sanitarias de la Nacion (National Sanitary Works Laboratory) Argentine Republic, for more than twelve years. The results have been very satisfactory. The basis of the method is the relative absorbing effect of muddy water on the light rays passing through it. Its two bands of Ught rays of equal intensity are allowed to pass through two glass containers of equal size, one containing the standard water and the other the water whose turbidity must be found, the intensities of the rays after passing through the containers will be inversely proportional to the respective water turbidities. In determining the index of turbidity with the use of the fototurbidimeter we compare natural water with the same water after filtering it through a candle filter to eliminate the suspended matter. The apparatus is provided with two iron rails 3 meters long supported on iron legs at 1.20 meters in height (figure 1). On the front rail a scale is engraved, the zero of it being in the middle of the rail. From the zero point to the rail ends, series of 0.5 cm. marks are made which serve to determine the position of the Bunsen Fotometer supported by a little car which slides upon the rails and to which an index is attached. At the rail ends two small size electric lamps are