The procedure for conducting a test for causticity with tannin is as follows:
1. Fill two test tubes to the first mark (25 ml) with some of the original boiler water sample, taking care not to disturb the settled sludge in the container. (Transfer as little sludge as possible from the sample-collecting container to the test tubes.)
2. Shake causticity reagent No. 1 thoroughly and add enough to each of the two marked tubes to bring the levels up to the second, or long, mark (30 ml). Stir both with the stirring rod, which must be kept clean and reserved for the causticity test only.
3. Stopper both tubes and let them stand until any sludge formed has settled to the bottom. The sludge carries down with it much of the tannin or other colored matter in the solution; settling takes a few minutes if the sample is warm.
4. Without disturbing the sludge at the bottom, pour enough solution from the tubes into the third marked tube to fill it to the second, or long, mark. Discard the mixture left in the first two. When the sample in the third tube is still warm, cool it by letting cold water run on the outside of the tube. It is sometimes possible to intensify the pink color by adding two drops of phenolphthalein from the indicator-dropping bottle to the sample in the tube. Stir the solution. When it is not pink, the causticity in the boiler water is zero.
5. When the sample is not pink, the test is finished. But if the mixture turns pink, proceed in the same manner as directed in Steps 3, 4, and 5 when no tannin is used.
Here is a brief explanation of an ALTERNATE PROCEDURE for making the test for causticity when tannin is used. In this procedure any glass container, such as a large test tube or graduated cylinder, marked for 50 to 60 ml can be used instead of the two standard marked test tubes used in Steps 1 and 2 above. With the large test tube or graduated cylinder, the warm (160F) sample is added up to the 50-ml mark and causticity reagent No. 1 up to the 60-ml mark. Stir the mixture and stopper the tube, or graduate. After the sludge settles, pour off enough of the solution into one of the standard marked test tubes to fill it to the long mark (30 ml). When the sample is warm, cool it by letting cold water run on the outside of the tube. Adding two drops of phenolphthalein may intensify the pink color. When the solution is not pink, the causticity in the boiler water is zero. But if it turns pink, proceed in the same manner as in Steps 3, 4, and 5 when no tannin is used. 1-32
The sample for this test should be cooled to 70F, or below, and exposed to the air as little as possible, because oxygen in the air combines with sodium sulfite in the sample and causes low readings. Collect a separate sample, using the boiler water sample cooler, with the line reading to the bottom of the sampling bottle. Allow the boiler water to run until a few bottlefuls overflow to waste.
The equipment necessary to make the sodium sulfite test is as follows:
Two marked test tubes
Two plain test tubes
One stopper for plain test tube
One stirring rod
One 8-in. dropper
One 1/4-measuring tsp
One 50-ml beaker
One 150-ml beaker
One 30-ml acid-dropping bottle, with dropper marked at 0.5 ml for hydrochloric acid 3N
One 30-ml starch-dropping bottle, with dropper marked at 0.5 ml for starch indicator
The reagents required are as follows:
One 2-oz bottle of potato, or arrowroot starch
One 8-ml vial of thymol
One 24-oz bottle of hydrochloric acid 3N
One 1-pt amber bottle of standard potassium iodate-iodide reagent
The starch indicator for this test must be prepared locally. The procedure to adhere for good results is as follows:
1. Measure out a level one-fourth tsp of potato or arrowroot starch and transfer it to the 50-ml beaker.
2. Add a few milliliters of distilled water and stir the starch into a thick paste, using the end of the stirring rod.
3. Put 50 ml of distilled water into the 150-ml beaker. (It is convenient in this step to have the 150-ml beaker marked at the point where it holds 50 ml, or one of the marked test tubes can be used by filling it with distilled water to the fourth mark above the long mark.)Continue Reading