摘要：In the examination of water, the standard of turbidity is the kaolin suspension of 1 g/L in Japan officially. In this method, the coefficient of variation is about 28% in intensity of turbidity of standard suspension prepared from various kaolin articles of commerce, and is about 8%, prepared from purified kaolin obtained through the sedimentation method (reference to report I). In the method that kaolin suspension is standardized by transmissible light path length in the standard turbidimeter based on"the standard methods for the examination of water and waste water of APHA" the coefficient of variation is about 3.9% in intensity of turbidity of standard suspension standardized. This standard turbidimeter is more convenient for routine works than the candle turbidimeter of"the standard methods of APHA" In stead of the standard turbidimeter, the transmittance grademeter with double cross mark is available as simple method, but in this case the coefficient of variation is about 8%. In the examination of transmittance grade of water by this transmittance grademeter with double cross mark, precision is higher than by the Japan water works association method with No. 5 type character mark.
