A new type of photoelectric nephelometer is described. The essential principle is the measurement of the intensity of scattered light coming from an illuminated column of turbid medium by a comparison with the light scattered from an invariable standard of turbidity (frosted glass) in a narrowly defined region of the spectrum with the aid of a quantitatively variable light diminution. Photoelectric cells are used to indicate equivalence of light.
The use of two photocells activated by light from a single source apart from eliminating the personal error in observations avoids the errors of instability due to intensity fluctuations of the light source. The measurement through a sensitive and objective method of photometry by physical means (in the form of a variable light diaphragm) and the use of light filters for measurements in narrowly defined regions of the spectrum give greater precision.
The accuracy of the apparatus is ± 2·4 per cent.
The several applications of the apparatus are described.