Specific Gravity, the ratio of the weight of one body to that of an equal volume of another, adopted as a standard of reference. For solids and liquids the standard is pure water, at a temperature of 60° F., the barometer being at 30 inches. Air is the standard for aeriform bodies. A cubic foot of water weighing 1,000 oz., if the same bulk of another substance, as for instance cast iron, is found to weigh 7,200 oz., its proportional weight or specific gravity is 7.2. It is convenient to know the figures representing this proportion for every substance in common use, that the weight of any given bulk may be readily determined ; and for all substances the specific gravity is used among other tests for the purpose of distinguishing bodies from each other, the same substance being found, under the same circumstances, to retain its peculiar proportional weight or density. Hence tables of specific gravity are prepared for reference, and in every scientific description of substances the specific gravity is mentioned. In practical use, the weight of a cubic foot is obtained from the figures representing the density by moving the decimal point three figures to the right, which obviously from the example above gives the ounces, and these divided by 16 the pounds avoirdupois, in the cubic foot.

Different methods may be employed to ascertain the specific gravity of solids. That by measuring the bulk and weighing is rarely practicable, nor is it desirable. As a body immersed in water must displace its own bulk of the fluid, the specific gravity may be ascertained by introducing a body, after weighing it, into a suitable vessel exactly filled with water, and then weighing the fluid which is expelled. The proportional weight is then at once obtained. Wax will cause its own weight of water to overflow; its specific gravity is then 1. Platinum, according to the condition it is in, will cause only from 1/21 to 1/21.5 of its weight of water to escape, showing its specific gravity to be from 21 to 21.5. But a more exact method than this is commonly employed. The difference of weight of the same substance, weighed in air and when immersed in water, is exactly that of the water it displaces, and may consequently be taken as the weight of its own bulk of water. The specific gravity then is obtained by weighing the body first in air, and then, suspended by a fibre of silk or a hair, in water, and dividing the weight in air by the difference.

If the body is lighter than water, it is to be attached to one heavier, to make it sink; then find the loss of the two by immersion, and also the loss of the heavier body; the difference will express the weight of water displaced by the lighter body, whose weight divided by this difference will give its specific gravity. It is hardly necessary to say that the substance examined must be free from mixture of foreign matters, and especially from cavities that may contain air. Minerals, if suspected to contain such, should be coarsely pulverized, and then the second method above may be conveniently applied to determine their density. The specific gravity of fine powders may be determined by one of the methods employed for ascertaining the specific gravity of fluids, viz. : by comparing the weight of a measured quantity with that of the same quantity of water. A glass vessel called a specific gravity bottle is commonly employed, which is furnished with a slender neck, upon which is a mark indicating the height reached by 1,000 grains of water.

The substance to be examined is introduced till it reaches the same mark, and, the weight of the empty bottle being known, only one weighing is required to obtain the result. - A common method for finding the specific gravity of fluids is by the instrument called a hydrometer or areometer, of which several kinds are in use, all dependent on the principle that the weights required to immerse a light body, as a bulb of glass, in different fluids, are proportional to the densities of these fluids. Such instruments are used for ascertaining the specific gravity of liquors, as an indication of their strength. (See Hydrometer.) Gaseous bodies are weighed in a thin glass flask or other vessel made for the purpose, and provided with a stopcock. The vessel is exhausted of air before the introduction of the gas. The experiment requires particular care, as the result will be found to vary under different conditions of pressure, temperature, and the hygrometric state of the atmosphere. The temperature of the air should be 60° and barometric pressure 30 inches.

The specific gravities may also be calculated from the atomic weights of the gases : when the atomic volume is equal to that of hydrogen, it is obtained by multiplying the specific gravity of hydrogen by the atomic weight of the gas; when the atomic volume is half that of hydrogen, the specific gravity of the gas is equal to the specific gravity of hydrogen multiplied by twice the atomic weight of the gas; and when the atomic volume is twice that of hydrogen, the specific gravity of the gas is equal to the specific gravity of hydrogen multiplied by half the atomic weight of the gas. - The proportions of two ingredients in a compound, as in an alloy of gold and silver, may be found by multiplying the specific gravity of each ingredient by the difference between it and the specific gravity of the compound. As the sum of the products is to the respective products, so is the specific gravity of the body to the proportions of the ingredients; then as the specific gravity of the compound is to the weight of the compound, so are each of the proportions to the weight of its material. - The following table presents the specific gravities of substances most likely to be referred to, collected from various sources.

The weight of a cubic foot in ounces avoirdupois is seen by moving the decimal point three figures to the right.

## Table Of Specific Gravities

 Acid, acetic..... 1.062 arsenic.......... 3.391 boracic, crystallized 1.479 boracic, fused... 1.803 citric..... 1.034 hydrochloric...... 1.200 nitric ...... 1.271 to1.583 aquia regia........ 1.234 phosphoric, liquid . 1.558 phosphoric, solid .. 2.800 sulphuric......... 1.841 Alabaster............ 1.874 Alcohol, absolute..... 1 792 of commerce...... 0.835 Ale or beer.......... 1.035 Alum.... 1.724 Aluminum___ 2.560 to 2.670 Amber........ 1.064 to 1.100 Ambergris...... 0.780 to 0.926 Amethyst, common... 2.750 oriental, or violet sapphire. 8809 to 4.160 Ammonia.... 0-75 Anthracite..... 1.360 to 1.850 Antimony........... 6.702 Asphaltum ... 0.905 to 1050 Barytes.... 4.000 sulphate of (heavy spar).... 4 300 to 4.720 Basalt............... 2.864 Beeswax...... 0.956 to 0.964 Bismuth... 9.822 Brandy... 0.837 Brass......... 7.824 to 8.396 Wire... 8.544 Brick..... 1.900 to 2.000 Bronze, gun metal.... 8.700 Butter............... 0942
 Cadmium.... 8.600 Caoutehoue... 0.933 Chalk............... 2.784 Cinnabar... 8.998 Clay................. 1.930 Coal.bituminous 1.020 to 1.350 Cobalt, cast........... 7.812 Copal................ 1.045 Copper, native... 8.940 cast............... 8.788 wire.............. 8.878 coin.............. 8.915 Coral......... 2.540 to 2.850 Diamond..... 3.521 to 3.550 Dolomite... 2.540 to 2.830 Earth, mean of the globe............ 5.210 Emerald...... 2.678 to 2.775 Ether.sulphuric 0.632 to 0.775 Fat of beef... 0.923 Feldspar......' 2.400 to 2.620 Freestone... 2.143 Garnet... 3.150 to 4.300 Glass, bottle.......... 2.733 Crown... 2.520 green............. 2.642 flint........ 2.760 to 3.329 plate ............. 2.760 plate of St. Gobain. 2.488 Gold, native. 15 15.600 to 19.500 pure, cast......... 9.258 hammered........ 19.362 coin.............. 17.647 22 carats fine...... 17.486. 20 carats fine...... 15.709 Granite, Quincy...... 2 652 Staten island...... 2.780 Graphite.... 1.987 to 2.400
 Grindstone... 2.143 Gunpowder, loose. 0.836 0.900 close shaken 0.937 to 1.000 solid... 1.550 to 1.800 Gum arabic.... 1.452 Gypsum, compact. to 1.872 2.288 Heliotrope or bloodstone...... 2.630 to 2.700 Hematite iron ore. to 4.500 5.300 Honey... 1.456 Hyacinth...... 4.000 to 4.750 Ice.... 0.930 Iodine................ 4.948 Iridium, hammered... 23.000 Iron, malleable. 7.645 to 7.817 cast............... 7.207 ore, magnetle 4.900 to 5.200 Ivory... 1.822 to 1.917 Lard............ ... 0.947 Lead, cast.... 1.350 to 11.445 white... 7.235 ore, galena.. 7.250 to 7.780 Lime, quick.......... 0.804 Limestone, compact.... 2.386 3.000 crystallized....... 2.722 Magnesia, carb. 2.222 to 2.612 Malachite... 3.700 to 4.000 Manganese ore (psilomelane)... 3.700 to 4.330 Marble, Carrara...... 2.716 Parian... 2.837 Egyptian......... 2.668 Mercury, common___ 13.568 pure.............. 14.000 Mlea... 2.750 to 3.100 Milk................ 1.032 Myrrh.... 1.360 Naphtha...... 0.700 to 0.847 Nickel, cast... 8.279 Nitre (saltpetre)... 1.900 Oil, castor... 0.970 linseed... 0940 olive... 0.915 turpentine... 0.870 whale............. 0.923 Opal................. 2.114 Opium............... 1.337 Palladium........... 11.800 Pearl, oriental.. 2. 510 to 2.750
 Peruvian bark... 0.784 Pewter.............. 7471 Phosphorus... 1770 Platinum, native., to 17.000 18.000 . refined............ 19.500 hammered... 20.336 wire.............. 21.041 laminated... 22.069 Porcelain, China... 2.385 Sevres............ 2.145 Porphyry ..... 2.458 to 2.972 Potassium... 0.865 Proof spirit... 0.923 Quartz........ 2.500 to 2.800 Rhodium... 11.000 Rosin... 1100 Ruby................ 4.283 Salt, common... 2.130 Sand......... 1.500 to 1.800 Sapphire, oriental .... 3.994 Serpentine .... 2.507 to 2.591 Silver, pure, cast... 10.474 hammered........ 10.510 coin.............. 10.534 Slate ......... 2.110 to 2072 Soapstone..... 2.650 to 2.800 Sodium... 0.972 Spermaceti... 0.943 Steel, hard... 7.816 to 7.840 Soft... 7.833 Sugar............. 1.696 Sulphur, native 2.033 fused............. 1.990 Tallow............... 0941 Tar ................. 1.015 Tellurium..... 5.700 to 6.115 Tin, cast... 7291 hardened ......... 7.299 Topaz......... 3.400 to 3.650 Tourmaline___ 2.940 to 3.300 Tungsten..... 17.490 Turquoise..... 2.600 to 2.830 Ultramarine.......... 2.362 Vinegar... 1.013 to 1.080 Water, distilled...... 1.000 sea............... 1.028 Dead sea.... 1.240 Wine, Burgundy..... 0.991 white champagne.. 0.997 Wood (see tables in article Fuel). Zinc, cast............. 7.190

## Specific Gravity #1

See Gravity, Specific.