TM 5-6630-215-12h.Turbidity, 0-500 FTU Range (fig. 2-11 and 2-12 para 2-18h).(1) Turbidity occurs in most surface waters as the result ofsuspended clay, silt, finely divided organic and inorganic matter,plankton and other micro-organisms.Turbidity measurement of water isimportant to those industries where the product is destined for humanconsumption,such as the food and beverage industries, and municipalwater treatment plants.(a) The turbidity test measures an optical property of thewater sample which results from the scattering and absorbing of lightby the particulate matter present.The amount of turbidity registeredis dependent on such variables as the size, shape, and refractiveindices of the particles.No direct relationship exists between theturbidity of a water sample and the weight concentration of thematter present, as is determined in the suspended solids test.(b) Turbidity calibrations were originally based on the Jack-son candle turbidimeter with results expressed in Jackson TurbidityUnits (JTU).As the Jackson equipment lacks sensitivity below 25 JTU(most treated water ranges from O to 5 JTU, the meter scale calibr-ations have been based on a uniform milky polymer called formazin,which allows accurate calibrations over a wide range.The results areexpressed as Formazin Turbidity Units (FTU) and are equivalent to theJackson units.(2) Turbidity Test Procedure.NOTEFiltering (para 2-22) is recommended for highlycolored samples.The filtered water is then usedin place of the clear, colorless water called forin step (b).(a) Take a water sample by filling a clean sample cell to the25 ml mark.(b) Fill another sample cell to the 25 ml mark with clear,colorless water and place it into the cell holder.Insert the Turbid-ity (Absorptometric Method) Meter Scale into the meter and adjust thewavelength dial to 450 nm.Adjust the light control for a meterreading of of zero FTU.((c)Replace the blank sample(step (c)) with the sample(step (a) in the cell holder and read the formazin turbidityunits (FTU).2-51
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