Thus
Weight in air 3.2170 grams
Weight in water 2.7050 "
------
Difference 0.5120 gram
3.2170/0.5120 equals 6.28, the sp. g.
The sp. g. of a substance depends mainly on its composition, but is
affected by certain conditions. The effect of temperature has been
already considered. Air holes and empty spaces lessen the specific
gravity of otherwise solid bodies; and metals, which after fusion become
imperfect solids, have their density increased by hammering or rolling.
But metals when free from pores have their density diminished when
rolled, without annealing. The effects of these conditions are slight
when compared with those due to the presence of impurities.
For simple substances, or mixtures of only two substances, a
determination of sp. g. is a sufficient check on the composition for
many practical purposes; and with more complex mixtures, such as slags
and some of the products of dressing operations in which the material
does not differ much in its nature from time to time, such a
determination will yield information of considerable value, and afford a
check upon the proper working of a process.
When the mixing of two substances is accompanied by a change in volume,
the sp. g. of the mixture can only be learnt by experiment. But when the
substances have no such action on each other the resulting sp.
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