--------------+----------------------------------------------- | Suspended Matters: Parts in 100,000. Turbidity, +----------------------------------------------- Platinum-wire | | River | River | River Standard. | Settled | Waters, | Waters, | Waters, | Waters. | Finest | Average | Coarsest | | Sediment. | Sediment. | Sediment. --------------+-----------+-----------+-----------+----------- 0.01 | 0.16 | | | 0.05 | 0.80 | 0.85 | 1.30 | 2.40 0.10 | 1.60 | 1.75 | 2.60 | 4.90 0.20 | 3.20 | 3.60 | 5.50 | 10.00 0.30 | 4.80 | 5.70 | 8.50 | 15.00 0.40 | 6.40 | 7.80 | 11.60 | 21.00 0.50 | 8.00 | 10.00 | 15.00 | 26.00 1.00 | 16.00 | 23.00 | 36.00 | 59.00 1.50 | 24.00 | 40.00 | 62.00 | 97.00 2.00 | 32.00 | 61.00 | 94.00 | 140.00 3.00 | 48.00 | 110.00 | 175.00 | 250.00 --------------+-----------+-----------+-----------+----------- SOURCE OF TURBIDITY. Much turbidity originates in plowed fields of clayey soil, or in fields upon which crops are growing. If it has not rained for some days, and the surface-soil is comparatively dry, the first rain that falls upon such land is absorbed by the pores of the soil until they are filled. If the rain is not heavy, but little runs off over the surface. If, however, the rain continues rapidly after the surface-soil is saturated, the excess runs off over the surface to the nearest watercourse. The impact of the rain-drops upon the soil loosens the particles, and the water flowing off carries some of them in suspension, and the water is said to be muddy. The particles carried off in this way are extremely small. Mr. George W. Fuller, in his report upon water purification at Louisville, estimates that many of them are not more than a hundred thousandth of an inch in diameter, and not more than a tenth as large as common water bacteria. The turbidity of the water flowing from a field of loose soil may be 2.00 or more; that is to say, the wire is hidden by a depth of half an inch of water or less. When the water reaches the nearest watercourse it meets with water from other kinds of land, such as woodlands and grassed fields, and these waters are less turbid. The water in the first little watercourse is thus a mixture and has a turbidity of perhaps 1.00.