I1
P

GENERAL OPERA TIONS '*7

grams and fractions. The generally approved method is to have.

the space between the central knife edge and the pan support

marked in ten principal divisions, each with ten subdivisions.

The number over the central pivot will then be 0 and that directly

over the pan will be 10. If the

rider is placed over the pan it

will have the same value as if it

were in the pan. Hence it should

weigh, in milligrams, whatever is

indicated by this number. Various

balances have, instead of 10, the

figures 5, 6 or 12 over the right

pan. They will then require

riders having these indicated

values, in milligrams.

The Chain Rider. — The
" Chainomatic " balance entirely
dispenses with a separate rider.
One end of a small gold chain is
permanently attached to the
balance beam. The other end
of this chain is fastened to a
hook which may be moved up
and down a scale (Fig. 16),
this action being controlled by
a knob outside the balance case.
Movement of the hook on the
scale varies in a definite manner
the length of side of the loop
which is supported by the beam
and this may be adjusted while
the beam is in motion. This
is a distinct advance in balance design, although this improve-
ment adds considerably to the cost of the balance.

Use of the Balance.—It has already been stated thai/ the
process of weighing involves the adjustment of weights upon
one pan until they are in equilibrium with the material on
the other pan. This is not done by noting when the? balance
beam fails to swing but by the more accurate method of causing

FIG. 10.—-"Chain ridor find part
of scale as used on tho "ehumonm-
tic" balance.

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