Hardness  buffer Hardness titrating solution The steps of the hardness test are as follows: 1. 2. 3. 4. Measure 50 ml of the sample in the graduated cylinder and transfer it to the casserole. With the calibrated dropper, add 0.5 ml of the hardness buffer reagent to the sample, and stir. Add  4  to  6  drops  of  hardness  indicator.  If hardness is present, the sample will turn red. Add  the  hardness  titrating  solution  slowly  from the  burette,  and  stir  continually.  When approaching the end point, note that the sample begins to turn blue, although you can still see a definite reddish tinge. The end point is the final discharge  of  the  reddish  tinge.  Adding  more hardness  titrate  solution  does  not  produce further  color  change. In using this procedure, add the hardness titrating solution  slowly  because  the  end  point  is  sharp  and rapid. For routine hardness determination, measure 50 ml of the sample, but add only approximately 40 to 45 ml to the casserole at the start of the test. The hardness buffer reagent and the hardness indicator should then be added as directed and the mixture titrated rapidly to the end point.   The  remaining  portion  of  the  sample should then be added. The hardness in the remainder of the sample will turn the contents of the casserole red again. Titrating is continued slowly until the final end point is reached. A record should be kept of the total milliliters of hardness titrating solution used. To calculate the results in ppm hardness, use the following equation: ppm hardness = ml titrating solution x 1,000 (CaCO₃)  (ml  sample) With  a  50-ml  sample,  the  hardness  in  ppm  as CaCO₃  is  equal  to  the  ml  of  titrating  solution  used, multiplied by 20. Test for Phosphate The   calorimetric   test   for   phosphate   uses   a decolorizing carbon to remove tannin. Carbon absorbs the tannin, and the carbon and tannin are then filtered out. When tannin is not present, carbon improves the test  for  residual  phosphate  by  making  the  tricalcium phosphate sludge more filterable. The equipment required for the phosphate test is as follows: One phosphate color comparator block of two standards—30 ppm and 60 ppm of phosphate as PO₄.   (The   Taylor   high-phosphate   slide comparator may be used instead.) Four   combination   comparator   mixing   tubes, each marked 5, 15, and 17.5 ml, with stoppers. One filter funnel, 65-mm diameter. One package of filter paper, 11 cm in diameter. One 20-ml bottle. One 0.5-ml dropper. One 1/4-tsp measuring spoon or spatula. Two plain test tubes, 22 mm by 175 mm (about 50 ml). Two rubber stoppers, No. 3 flask. One  250-ml  glass-stoppered  bottle  or  flask, labeled comparator molybdate reagent. The reagents you need are as follows: One 32-oz comparator molybdate. One  2-oz  concentrated  stannous  chloride. One 32-oz standard phosphate test solution (45 ppm of phosphate, PO₄). One pound decolorizing carbon. (This is a special grade  of  decolorizing  carbon  tested  to  make  sure  it does  not  affect  the  phosphate  concentration  in  the sample.) For test purposes, the stannous chloride is supplied in concentrated form. The reagent must be diluted and should  be  prepared  from  the  concentrated  stannous chloride on the day it is to be used, because the diluted solution  deteriorates  too  rapidly  for  supply  by  a  central laboratory.   If   not   fresh,   diluted   stannous   chloride gives low test results. Concentrated stannous chloride also deteriorates and should not be used if more than 2 months old. The  procedure  for  making  diluted  stannous chloride is as follows: 1. Fill the 1/2-ml dropper up to the mark with the concentrated stannous chloride. 2. Transfer it to a clean 20-ml bottle. 3.  Add  distilled  water  up  to  the  shoulder  of  the bottle, then stopper and mix by shaking. 1-29