1.   Pipette 50 ml of the sample into a 6-inch white porcelain evaporation dish. 2.   Place the same quantity of distilled water into a second dish for color comparison. 3.   To both dishes, add 1 ml of potassium chromate. Titrate the dish with the sample. Add standard silver nitrate solution (2.4 grams per liter) from a burette, a few drops at a time, with constant stirring until the first permanent  reddish  coloration  appears.  (This  can  be determined by comparison with the distilled water blank.) Record the ml of silver nitrate used. 4.   If more than 7 or 8 ml of silver nitrate solution is required, the entire procedure should be repeated by using a smaller sample diluted to 50 ml with distilled water. CALCULATIONS—When making calculations for chloride, use the formula below. ml of AgNo₃ used - 0.2 × 500 Ppm chloride (C l) = ml of sample Three precautions to bear in mind are as follows: 1. If the sample is highly colored, it should be decolorized  by  shaking  with  washed  aluminum hydroxide and filtering. 2. If the sample is highly acid, add 10 percent sodium carbonate solution until it is slightly alkaline to methyl orange. 3. If the sample is highly alkaline, add diluted sulfuric acid until it is just acid to phenolphthalein. The Sulfate Test The  sulfate  test  determines  whether  sulfates  are present  in  sufficient  quantities  in  water  to  cause undesirable physiological effects because sulfates can cause diarrhea in human beings. In the sulfate test, the sulfate value is found by trial, as the test merely determines approximate values. For this reason, you may have to repeat the test several times. The test is begun by testing for sulfates at 100 ppm as follows: 1.   Fill a clean test bottle to the 100-ml mark with the water sample. 2.   Add 1 ml of barium chloride solution to the same and  use  a  barium  chloride  pipette.  Shake  intermittently  for 10 minutes. 3.   Tear a piece of filter paper into small pieces and place the pieces in the solution. 4. Shake the bottle for 5 minutes or until the paper becomes fluffy and gelatinous. 5.   Place a funnel and filter paper in a second bottle. 6. Filter about 25 ml of the sample into the second bottle. Rinse the second bottle with this amount of filtrate, and discard the filtrate. Replace the funnel and continue filtration until 50 ml of filtrate is collected. 7.   Add 1 ml of barium chloride solution to the filtrate with the barium chloride pipette. Shake for 5 seconds, and observe immediately for a precipitate or clear solution. If a clear solution is obtained, record the sulfates as less than 100 ppm. As an immediate precipitate or milky solution indicates the sulfates are greater than 100 ppm, a new sample must be tested for 200-ppm sulfate. For each additional 100-ppm sulfate test required, add 1 ml of barium chloride solution. Therefore, 3 ml of barium chloride solution must be added to test for 300-ppm sulfate. However, the 1 ml of barium chloride solution added after filtration is not changed. If a clear solution is obtained, the sulfates are less than the ppm for which they were tested, and the value is recorded  as  being  between  the  values  of  the  last preceding tests. A precipitate or milky solution requires that a new sample of the water be tested for the next higher value. COLOR TEST Color  in  water  is  due  to  various  materials  in  solution, although suspended turbidity occasionally adds an apparent color to water that may add to or disguise the true color. In water with low turbidity, the apparent color corresponds closely to the true color. However, if turbidity is high, the apparent color may be misleading. To determine the true color, first filter the water through clean white filter paper before it is compared with the standards.  Because  the  filter  paper  often  removes  some true color from the first portion of the sample, discard the first 100-ml which pass through the filter and use the next portion for the color comparison. Make the color determination by matching the sample color with color standards in a color comparator. TASTE, ODOR, AND THRESHOLD ODOR TEST Unless the water has a definite taste (sweet, sour, salty,  or  bitter),  the  sensation  produced  upon  the  observer is generally due to the presence of odor, rather than taste. These two senses work in unison. Sulfur water, for instance, apparently tastes “terrible” when it is really only its rotten egg odor that is registering on our senses. 7-24