, as the portion of the assay solution contains,
and then water is added until the solutions are of nearly equal bulk.
Next, a standard solution of the metal being estimated is run in from a
burette, the mixture being stirred after each addition until the colour
approaches that of the assay. The bulk of the two solutions is equalised
by adding water. Then more standard solution is added until the tints
are very nearly alike. Next, the amount added is read off from the
burette, still more is poured in until the colour is slightly darker
than that of the assay, and the burette read off again. The mean of the
readings is taken, and gives the quantity of metal added. It equals the
quantity of metal in the portion of the assay. If this portion was
one-half of the whole, multiply by two; if one-third, multiply by three,
and so on. When the quantity of metal in very dilute solutions is to be
determined, it is sometimes necessary to concentrate the solutions by
boiling them down before applying the re-agent which produces the
coloured compound. Such concentration does not affect the calculations.
~Gasometric Assays.~--Gasometric methods are not much used by assayers,
and, therefore, those students who wish to study them more fully than
the limits of this work will permit, are recommended to consult Winkler
and Lunge's text-book on the subject.
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