With respect to the delay which must take place during the titration in
order to give the precipitate time to fall, it is advantageous, in order
to save time, to work with several samples; but it is, in such a case,
desirable to have a separate burette for each sample, in order to avoid
noting every addition of the chameleon solution and afterward adding
them up. If burettes are wanting, and one must be used for several
samples, a Mohr's burette with glass cock is the most convenient to
use. For the titration of iron with chameleon solution, the latter is
commonly used of such a strength that 0.01 gramme of iron corresponds to
about one cubic centimeter of chameleon solution, which is obtained
by dissolving 5.75 grammes permanganate of potash in 1,000 cubic
centimeters water. The titration is determined by means of iron, a salt
of iron or oxalic acid. A drop of such a solution, corresponding to
about one-twentieth cubic centimeter, or 0.0001 gramme Mn, is sufficient
to give a perceptible reddish color to 200 cubic centimeters of water.
As what takes place in the titration of iron with chameleon is indicated
by the following formula,
10FeO + 2KMnO_{4} = 5Fe_{2}O_{3} + K_{2}O + 2MnO_{2},
it appears, on making a comparison with the formula given above, that
ten equivalents of iron correspond to three equivalents of manganese,
and that there is thus required for three equivalents manganese as
much chameleon solution as for ten equivalents iron.
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