The bottle is wiped with a
soft, dry cloth, taking care not to squeeze or warm the bottle. The
bottle will remain filled to the top of the stopper. It is allowed to
stand in the balance box for a minute or two, and then weighed.
Distilled water, as stated, should be used; the use of ordinary water
may increase the weight by 5 or 6 milligrams. Many waters, if they have
not previously been boiled, give off bubbles of air which render the
weighing worthless.
The temperature of the water is of greater importance; lowering the
temperature 2° will increase the weight by 10 or 12 milligrams. A beaker
of water may be warmed or cooled to the required temperature; then the
bottle is filled from it, and quickly weighed. If the balance-room is
cooler than the water, the latter will draw back into the bottle, and a
few small bubbles of air will enter; but even in extreme cases this will
only increase the weight by a very small fraction of a milligram. There
is more trouble caused when the room is warmer, for the liquid then
expands and protrudes as a drop resting on the top of the stopper.
There will in this case be loss by evaporation, which in the case of the
more volatile liquids, such as alcohol, is serious. To prevent this
loss, as well as any that may arise by overflow, the stopper should be
dilated above into a small cup, A (fig.
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