CAUTION Any  diluted  stannous  chloride  not  used the day it is made should be discarded. The following procedure is used to make the test for phosphate: 1. Without disturbing any settled sludge, transfer enough of the sample to the test tube to till it about half full. 2.   Add 1/4 tsp of decolorizing carbon. Stopper the tube  and  shake  vigorously  for  about  1  minute.  The carbon absorbs the tannin so it can be filtered out. 3.  Fold  a  filter  paper  and  place  it  in  the  filter funnel.  Do  not  wet  down  the  filter  paper  with  water. Filter the shaken sample, using a combination mixing tube as a receiver. The carbon absorbs tannin, and the tannin and sludge present are filtered out more rapidly. Avoid  jiggling  the  funnel,  as  unfiltered  boiler  water may overflow the edge of the filter paper into the tube. You have to support the funnel. 4.   After 5 ml of the sample has filtered through, as indicated by the level in the tube, discard it. Continue filtering to bring the level in the test tube again up to the 5-ml mark. The sample should come through clear and free, or nearly free, of any color from the tannin. If not nearly free of tannin color. repeat the test, using 1/2 tsp of carbon. adding it in two 1/4-tsp portions, shaking it for 1 minute after each addition. 5.   Add  the  comparator  molybdate  reagent  to  bring the level up to the second mark ( 15 ml). Stopper and mix by inverting the tube several times. 6.  Add  fresh  diluted  stannous  chloride  up  to  the third mark (17.5 ml). Stopper and mix by inverting. If phosphate is present, the solution in the mixing tube turns blue. 7.  Place  the  tube  in  the  comparator  block. Compare the color of the solution in the tube with the standard  colors  of  the  phosphate  color  block.  Colors between  the  two  standard  colors  may  be  estimated. Take  the  reading  within  1  minute  after  adding  the stannous chloride, because the color fades quickly. 8. Record the results as LOW, if below 30 ppm; HIGH, if above 60 ppm, or OK, if between 30 and 60 ppm. Test for Tannin The purpose of the TANNIN TEST is to determine the amount of tannin in the boiler water. Tannin holds sludge  in  suspension.  In  treating  boiler  water  with tannin,  control  the  dosage  by  the  depth  of  brown formed in the boiler water by the tannin. To estimate the depth of the color, which is necessary in adjusting tannin dosages, compare a sample of the boiler water with a series of brown color standards of successively increased depths of color. A tannin color comparator, which is used for the comparison, has five glass color standards:  No.  1,  very  light;  No.  2,  light:  No.  3, medium; No. 4, dark; and No. 5, very dark. The kit for the tannin test contains the following: One tannin color comparator Two square tubes, 13-mm viewing depth One plain test tube, 22 mm by 175 mm One filter funnel, 65 mm by 65 mm One package of filter paper, 11 cm in diameter making  this  test,  you  first  fill  a  plain  test  tube almost to the top with cool boiler water. Then place a square test tube in the slot of the comparator, and insert the filter funnel in it. Fold a filter paper and place it in the funnel without wetting it down. Filter water from the plain test tube into the square tube until the tube is neatly  full.  Remove  the  square  tube  from  the comparator and hold it up to a good source of natural light. Note the appearance of the filtered boiler water. Is it free of suspended solids and sludge? If not, refilter the  sample,  using  the  same  funnel  and  filter  paper. Repeat, using a double filter paper if necessary, until the sample does come through free of suspended solids and  sludge. To  complete  the  test,  place  the  square  tube  of filtered  sample  in  the  middle  slot  of  the  comparator. Then  compare  the  color  of  the  sample  with  the  five standards, viewing it against a good source of natural light.  The  color  standard  most  closely  matching  the color  of  the  filtered  sample  gives  the  tannin concentration  of  the  boiler  water.  For  a  number  of boiler  water  conditions,  the  tannin  dosage  is  usually satisfactory  if  it  maintains  a  medium  (No.  3)  tannin color. If the tannin color is too high, blow down; if too low, add tannin. Test for Caustic Alkalinity (OH) without Tannin The boiler water sample for this test is collected at a temperature of 70°F or below. 1-30