160│ 68.7 180│ 62.4 200│ 57.4 250│ 49.1 300│ 43.2 350│ 38.8 400│ 35.4 500│ 30.9 600│ 27.7 800│ 23.4 1000│ 20.9 1500│ 17.1 2000│ 14.8 3000│ 12.1 ───────────────────────────────────┴─────────────────────────────────── _Procedure._—Lower the rod vertically into the water as far as the wire can be seen and read the level of the surface of the water on the graduated scale. This will indicate the turbidity. The following precautions shall be taken to insure correct results: Observations shall be made in the open air, preferably in the middle of the day and not in direct sunlight. The wire shall be kept bright and clean. If for any reason observations cannot be made directly under natural conditions a pail or tank may be filled with water and the observation taken in that, but if this is done care shall be taken that the water is thoroughly stirred before the observation is made, and no vessel shall be used for this purpose unless its diameter is at least twice as great as the depth to which the wire is immersed. Waters which have a turbidity greater than 500 shall be diluted with clear water before the observations are made, but if this is done the degree of dilution shall be reported. TURBIDIMETRIC METHOD.