9971|| 50° |0.9881
15° |0.9991|| 30° |0.9957|| 100° |0.9586
-----------+------++-----------+------++-----------+-------
If, for example, a substance at 50° C. has a sp. g. of 0.9010 as
compared with water at 50° C., it will have (compared with water at 4°
C.) a sp. g. of 0.9010?0.9881; or 0.8903. The figures 0.8903 represent
the sp. g. of the substance at 50° C. compared with water at 4° C.
Except in comparing the sp. gravities of the same substance at different
temperatures, a calculation of this kind serves no useful purpose.
_In taking the specific gravity of a solid not in powder_, a lump of it
is freed from loose particles and its exact weight determined. By means
of a horse hair with a slip knot it is suspended to the balance, and
beneath it is placed, out of contact with the balance pan, a beaker of
distilled water. The horse hair must be long enough to keep the mineral
well beneath the surface of the water so as to allow the balance to
vibrate. Air bubbles are removed by touching with a camel-hair pencil.
Whilst the mineral is suspended in water the weight is again taken. It
will weigh less than before, and the difference between the two
weighings gives the weight of water (and consequently the volume)
displaced by the mineral. The weight in air divided by the difference is
the specific gravity.
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