USGS-NWQL: I-1250: Color, water, VIS_COMP
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Official Method Name
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Color, electrometric, visual comparison |
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Current Revision
| Revised 1985 |
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Media
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WATER |
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Instrumentation
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Visual Comparison |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Methods for the Determination of Inorganic Substances in Water and Fluvial Sediments, Techniques of Water-Resources Investigations of the United States Geological Survey, Book 5, Chapter A1 Edited by Marvin J. Fishman and Linda C. Friedman |
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Brief Method Summary
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The color of the water is compared to that of colored glass disks that have been calibrated to correspond to the platinum-cobalt scale of Hazen (1892). The unit of color is that produced by 1 mg/L of platinum. A small amount of cobalt may be added to aid in color matching. The Hazen scale (platinum-cobalt units) is usually satisfactory for most waters, but the hues and shades of some waters may not easily be compared with standards. If the hue of the water does not compare with that of the standard, very little can be done except to visually compare the absorbances of the sample and standard. Highly colored waters should not be diluted more than necessary because the color of the diluted sample often is not proportional to the dilution. |
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Scope and Application
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This method may be used to measure the color of water whose color reasonably matches from 1 to 70 units of the Hazen scale (Hazen, 1892) and that contains no excessive amount of sediment. Samples that have a color unit value greater than 70 must first be diluted. |
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Applicable Concentration Range
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25569 |
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Interferences
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Turbidity generally causes the observed color value to be greater than the true color value, but there is some disagreement as to the magnitude of the effect of turbidity. The removal of turbidity is a recurrent problem in the determination of color. Color is removed by absorption on suspended material. Filtration of samples to remove turbidity frequently removes some of the color-imparting solutes by absorption on the sediments or on the filter medium. Centrifuging is preferable to filtration, but centrifuging may not be completely effective in removing very finely divided particles. Flocculation of the dispersed particles with a strong electrolyte has been proposed (Lamar, 1949) and is sometimes effective. The process of flocculation decolorizes some waters and is, therefore, not suitable in all cases. |
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Quality Control Requirements
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Calibrate instrument using calibration standards (CAL). Quality control samples (QCS) and laboratory blanks (LB) analyzed at a minimum of I each after every 10 samples. (Reference OFR 95-443). |
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Sample Handling
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Container Description: 250 mL Polyethylene bottle. Treatment and Preservation: Use unfiltered sample to rinse bottles, then chill collected sample and maintain at 4 deg C; ship immediately. |
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Maximum Holding Time
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30 days |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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