If it be required to weigh a substance in water, or in any other liquid, that substance may be suspended in a vessel containing tin liquid by a horse-hair attached below the scale opposite to that freer whence the wire before mentioned was suspended ; and its weight while immersed in the liquid may be found to the hundredth part of grain, as in the former case. The reason why horse-hair is employ« to suspend the substance in water is, that it has very nearly the earn specific gravity as that fluid.
A solid body having greater specific gravity than water being thee weighed both in air and water, may have its specific gravity deter mined, that of the water being supposed to be known or assumed, the following proportion :— The weight lost by immersion in water (that is, the weight of water equal in volume to the volume of the solid [Ilsnitosvasics]), Ia to the weight of the body in air, As the specific gravity of the water is to that of the body.
The weight ofThe specific The weight I The specificOr, all equal bulk : gravity of : of the body : gravity of water. water =1'000 in sir. required.
The specific gravity of a fluid is found by weighing any one and thy same solid body in air, in water, and also in the fluid, and observing the two differences of weight. These differences are the weights o quantities of the two fluids which are equal in volume to the soli( body ; and they are to one another as the specific gravities of tho tw4 fluids : hence that specific gravity which was required may be found [See also ]1YDROSTATICILL It should be observed that the spocift gravity of the solid must greater than that of either of the fluids in order that the solid may sink when immersed in them.
The specific gravity of a liquid may be conveniently determined Is means of a rpecijir ;rarity bottle, a light bottle containing exacta; 1000 grains of distilled water at 60', to that when the bottle is fine', with the liquid whose specific gravity is to bo determined, the weigh in grains of the liquid determines the specific gravit; required. There is usually a counterpoiee for the weight of the empty Soule. If such a bottle be counterpoised and then be filled with pure alcohol it will weigh only 792 grains, thus giving 0.7'J2 as the specific ;rarity of the alcohol. If the bottle were filled with sulphuric acid it would weigh 1845 grains, so that 1.845 would be the specific gravity of the acid. In some cases bottles containing only 100 or 200 grains
may be used with advantage.
'the density of n powder not soluble in water may be ascertained by means of the specific gravity bottle, or if soluble in writer spirits of wine, oil of turpentine, or some other liquid, may be employed. But suppose the powder to be sand, we weigh into the 1000 grain bottle may 150 grains of the sand. If the sand had not displaced any of the water the bottle, when filled tip, would weigh 1150 grains; but it is found to weigh only 1006 grains, so that the sand has displaced 54 grains of water. Hence if the body whose specific gravity is to be found be a solid lighter than water, there must be annexed to it, before it is weighed, a mass of some material of known specific gravity, and such that the two bodies may together sink in the water. The compound mass, and the heavier body alone, must bo weighed both in air and water ; also the lighter body must be weighed in air. Let w be the weight of the com pound mass in air, and w' the weight of the same mass in water ; also let to bo the weight of the heavier body in air, and w' the weight of the same body in water : then w—w' is the weight of water equal in volume to the compound body, and to—w' is the weight of water equal in volume to the heavier body. The difference between w—w' and w—to is the weight of water equal in volume to the lighter body; therefore, by hydrostatics, that difference is to the specific gravity of water as the weight of the lighter body is to its specific gravity.
When the body is soluble in water, it may be weighed in air, and also in some fluid whose specific gravity is known, and which is not capable of dissolving it ; then its specific gravity may be found by the first of the above-mentioned rules, substituting the weight lost in the fluid for the weight lost in water.
If the solid body imbibes water without being dissolved in it, let it be weighed when perfectly dry, and call that weight w : again, we find the weight of water displaced by the body when dry, and call it n; then n is to w as the specific gravity of water is to the specific gravity of the body in its actual state. But D— NV is the weight of the water displaced by the solid part only of the body ; therefore n—w is to w as the specific gravity of water is to the specific gravity of the solid part only of the body.