and that, consequently, the unknown solution contained a little less
than 1 gram of iron; or, at least, he could not say it except he (or
some one else) had determined it by experiment. But if on dissolving 1
gram of iron, he found it to require 100.6 c.c. of the solution, and in
another experiment with 0.8 gram of iron that 80.5 c.c. of the solution
were required, he would be justified in stating that _the volume of
solution required is proportional to the quantity of metal present_.
There are a large number of volumetric assays of which this is true, but
that it is true in any particular case can only be proved by experiment.
Even where true it is well not to rest too much weight upon it, and in
all cases the quantity of metal taken, to determine the strength of the
solution used, should not differ widely from that present in the assay.
There are certain terms which should be explained here. When the
solution of a reagent is applied under such conditions that the volume
added can be correctly determined, the operation is called "titrating,"
the solution of the reagent used the "standard solution," and the
process of determining the strength of the standard solution is
"standardising." The "standard" is the quantity of metal equivalent to
100 c.c. of the standard solution.

~Standard Solutions.~--In making these the salt is accurately weighed
and transferred to a litre flask, or to the graduated cylinder, and
dissolved. The method of dissolving it varies in special cases, and
instructions for these will be found under the respective assays.
Generally it is dissolved in a small quantity of liquid, and then
diluted to the mark. For those substances that require the aid of heat,
the solution is made in a pint flask, cooled, and transferred; after
which the flask is well washed out. After dilution, the liquids in the
measuring vessel must be thoroughly mixed by shaking. This is more
easily and better done in the cylinder than in the litre flask. The