Having taken down the figures, confirm them by reading off
the weights as you put them back into the box. Do not rest a weight on
the palm of your hand for convenience in reading the mark upon it.
Remember one weight lost from a box spoils the set. Do not take it for
granted that the balance is in equilibrium before you start weighing:
try it.
[Illustration: FIG. 26.]
~Measuring Liquids.~--For coarse work, such as measuring acids for
dissolving ores, graduated glasses similar to those used by druggists
may be used. It is well to have two sizes--a smaller graduated into
divisions of 5 c.c. (fig. 26), and a larger with divisions equal to 10
c.c. No measurement of importance should be made in a vessel of this
kind, as a slight variation in level causes a serious error.
~Graduated flasks~ must be used when anything has to be made up to a
definite bulk, or when a fixed volume has to be collected. If, for
example, a certain weight of substance has to be dissolved and diluted
to a litre, or if the first 50 c.c. of a distillate has to be collected,
a flask should be used. Each flask is graduated for one particular
quantity; the most useful sizes are 1000 c.c., 500 c.c., 200 c.c., 100
c.c., and 50 c.c. The mark should be in the narrowest part of the neck,
and should be tangential to the curved surface of the liquid when the
flask _contains_ the exact volume specified.
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