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# Density

Density, of any substance, means the amount of matter contained in unit-volume. The amount of matter is expressed in units of mass such as the pound or the gramme, and the unit-volume taken is the cubic foot, cubic inch, or the cubic centimetre. If the substance is not of uniform density throughout - that is to say, if different values of the density be obtained for different volumes chosen - the result obtained in any case can only be said to give an average value of the density in that chosen portion. Adopting the gramme and cubic centimetre as units, the density becomes the number of grammes per cubic centimetre. One cubic centimetre of water has one gramme mass, so that in this way we see that the density would mean the mass of the substance divided by the mass of an equal volume of water. This ratio is otherwise termed the specific gravity of the substance. The following is a table of densities of the more important substances, compared with water at 4° C.: -

Solids.
Platinum (rolled) - 22.1
Gold - 19.3
Silver - 10.5
Copper - 8.8
Bronze Coinage - 8.7
Brass - 8.4
Steel - 7.8
Iron, Wrought - 7.8
Iron, Cast - 7.2
Tin - 7.3
Zinc - 6.9
Diamond - 3.5
Flint-glass - 3.3
Marble - 2.8
Aluminum - 2.7
Porcelain - 2.4
Ivory - 1.9
Anthracite Coal - 1.8
Sodium - 1.0
Ice - 0.9
Potassium - 0.9
Oak - 0.8
Pine - 0.6
Lithium - 0.6
Cork - 0.2

Liquids.
Mercury - 13.59
Bromine - 2.96
Sulphuric Acid - 1.84
Glycerine - 1.26
Blood - 1.06
Milk - 1.03
Sea-Water - 1.03
Olive-Oil - 0.92
Oil of Turpentine - 0.87
Petroleum - 0.84
Alcohol - 0.79
Ether - 0.71

Gases (q.v.) are usually compared with hydrogen, the lightest of known substances.