Hardness titrating solution
The steps of the hardness test are as follows:
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
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
One phosphate color comparator block of two
standards30 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
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
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.