5H_{2}O) in 1 litre of water. 2.
Dilute sulphuric acid, made by adding one part of the acid to three of
water, and titrating with the permanganate solution till a faint pink
persists after warming for several hours. 3. Starch paste. 4. Potassium
iodide solution.
Take 250 c.c. of the water in a stoppered bottle, add 10 c.c. of
sulphuric acid and 10 c.c. of the permanganate, and allow to stand in a
warm place for four hours. Then add a few drops of the solution of
potassium iodide, and titrate the liberated iodine with "hypo," using
starch paste towards the end as an indicator. To standardise the
hyposulphite, take 250 c.c. of water and 10 c.c. of sulphuric acid, and
a few drops of potassium iodide; then run in 10 c.c. of the
"permanganate" solution, and again titrate; about 30 c.c. of the "hypo"
will be used. The difference in the two titrations, divided by the last
and multiplied by 10, will give the c.c. of permanganate solution used
in oxidising the organic matter in the 250 c.c. of water. Each c.c.
represents 0.04 parts of oxygen in 100,000.
~Metals.~--These may for the most part be estimated colorimetrically.
~Lead.~--Take 100 c.c. of the water in a Nessler tube, and add 10 c.c.
of sulphuretted hydrogen water, and compare the tint, if any, against a
standard lead solution, as described under _Colorimetric Lead_.
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