003
per 100,000 are suspicious.
~Organic Matter.~--The organic matter cannot be determined directly; but
for ordinary purposes it may be measured by the amount of permanganate
of potassium which it reduces, or by the amount of ammonia which it
evolves on boiling with an alkaline permanganate of potassium solution.
A. _Albuminoid Ammonia._--To the residue left after distilling the
ammonia add 50 c.c. of a solution made by dissolving 200 grams of potash
and 8 grams of potassium permanganate in 1100 c.c. of water, and rapidly
boiling till the volume is reduced to 1 litre (this should be kept in a
well stoppered bottle, and be occasionally tested to see that it is free
from ammonia). Continue the distillation, collecting 50 c.c. at a time,
until the distillate is free from ammonia. Three or four fractions are
generally sufficient. Determine the ammonia colorimetrically as before.
If the total albuminoid ammonia does not exceed 0.005 in 100,000, the
water may be regarded as clean as regards organic matter; if it amounts
to more than 0.015, it is dirty.
B. _Oxygen Consumed._--A standard solution of permanganate of potash is
made by dissolving 0.395 gram of the salt in water and diluting to 1
litre. Each c.c. equals 0.1 milligram of available oxygen. The following
are also required:--1. A solution of sodium hyposulphite containing 1
gram of the salt (Na_{2}S_{2}O_{3}.
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