Always have the balance
at rest when putting on or taking off anything from the pans. Put the
weights on systematically. In using the rider (except you have a reason
to the contrary), put it on at the 5; if this is too much, then try it
at the 3; if then the weights are too little, try at the 4, if still not
enough, the correct weight must be between the 4 and 5; try half-way
between.
It is best to work with the balance vibrating; equilibrium is
established when the vibration to the left is the mean of the preceding
and succeeding vibrations to the right. For example, if it vibrates 6
divisions to the right on one swing, and 5 divisions on the next, the
intermediate vibration to the left should have been 5-1/2.
Note whether the substance increases in weight whilst on the balance. If
it does it may be because it was put on warm, and is cooling, or it may
be because it is taking up moisture from the air. Substances which take
up moisture rapidly should be weighed in clipped watch-glasses or in
light-weighing bottles or tubes.
Students, in recording the weights, should first read off those missing
from the box, writing down each order of figures as determined; first
tens, then units, and so on. Remember that the first four platinum
weights give the figures of the first place of decimals, the second four
give the second place, and that the third and fourth places are given by
the rider.
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