Specific Gravity
Specific Gravity, the ratio of the weight of a given volume of a substance to the weight of the same volume of a standard such as water or air. Water is the standard of comparison for liquids and solids; air is the standard for gases. Because it actually expresses the density of a substance compared to the density of the standard, specific gravity is sometimes called relative density. Thus, to say that aluminum has a specific gravity of 2.70 means that the density of aluminum is 2.70 times the density of water.
Specific gravity measurements are widely used in chemistry, mining, and metallurgy to aid in finding the purity and composition of materials. A solid can be checked by comparing its weight with the weight of an equal volume of water. For liquids, a hydrometer is often used. The specific gravity of a gas can be found by weighing equal volumes of the gas and dry air, with both at the same temperature and pressure.
Some approximate specific gravities are given below.
Liquids and Solids (Water=1.00)Alcohol, ethyl0.79Aluminum2.70Balsa wood (dry)0.16Copper8.96Ebony (dry)1.0Glycerine1.26Gold19.3Ice0.92Iron7.87Kerosene0.81Lead11.4Lithium0.534Magnesium1.74Mercury13.5Milk1.05Oak (dry)0.76Salt, common2.17Silver10.5Gases (Air=1.00)Carbon dioxide1.53Chlorine2.49Helium0.138Hydrogen0.070Methane0.554Nitrogen0.967Oxygen1.11Radon7.53