Determine the alkalinity in presence of methyl orange (see p. 37) in the
original sample and also in the sample after boiling, cooling, restoring
to the original volume with boiled distilled water, and filtering. The
difference between the two, if any, is the temporary hardness. This is
the most accurate method of determining the temporary hardness of
ordinary waters. Iron bicarbonate is included as a part of the temporary
hardness.