HYDROCARBURETS. Compounds of hydrogen and carbon. These appear to be several definite combinations of these elements ; among them the follow ing deserve especial notice : 1. Light car buretted hydrogen gas, which is the fire damp of coal mines and of marshes : 100 cubic inches weigh about 17.4 grains. It consists of two atoms of hydrogen = 2, and 1 of carbon = 6 ; its equivalent is 8. It burns with a pale blue flame. 2. Olefiant gas, which is formed during the distilla tion of equal measures of alcohol and sul phuric acid : 100 cubic inches weigh 30.5 grains. It is composed of 2 atoms of hydrogen = 2, and 2 of carbon = 12 ; and its equivalent, therefore, is 14. It burns with a bright white flame. Coal gas con sists of a mixture of these two hydrocar bons. The term olefiant gas is derived from the action of chlorine upon it, which, when mixed with the gas over water, gradually condenses it into a liquid looking like oil, which is a hydrochloride of carbon: 3. Quadricarburetted hydro gen, which is produced during the de structive distillation of oil (Faraday, An seals of Philosophy, xxvii„ 44), and NilliCh is a vapor condensable at 0°, of which 100 cubic inches weigh 61.2 grains. It con sists of 4 atoms of hydrogen = 4, and 4 of carbon = 24 ; and Its equivalent is 28. It burns with a dense and very smoky flame. This compound has also been called etherine, 1 volume of the vapor of of ether being constituted of 1 volume of quaclrihydroearbou and 1 of water vapor. 4. Bicarburet of hydrogen, obtained, like the last, from the volatile products formed during the destructive distillation of whale oil. When the qnadrihydrocarbon has been distilled off from the more vola tile portion, that which remains yields a product which congeals at 0°. It is a brittle white solid at that temperature : 100 cubic inches of its vapor weigh 85-3 grains, and it consists of 3 atoms of hy drogen = 3, and 6 of carbon = 36 ; its equivalent, therefore, is 39. These are the principal forms of hydrocarbon which have been satisfactorily identified : they all afford carbonic acid and water when burned in a sufficiency of oxygen ; and the proportions in which these are formed, together with the specific gravities of their respective vapors, furnish the data upon which their composition is estima ted. See NAS'TRA and N4 APTHALLN.
HYDROMETER. An instrument for de termining the specific gravities of liquids, and thence the strengths of spirituous liquors ; these being inversely as their specific gravities. Various instruments of different forms have been proposed for ascertaining readily the specific gravi ties of fluids ; but as Sikes's hydrometer is directed by act of parlia ment to be used in collect ing the revenue of Great Bntain, it may be consider ed as more deserving of de scription than any of the oth ers. This instrument is rep resented in the annexed fig ure. A B is a flat stem, divi ded on both sides into eleven equal parts, each of which is again subdivided into two.
The stem carries a hollow brass ball B C, in which is fixed a conical stalk C D, ter minating in a pear-shaped bulb D. Eight different weights of a circular form, and marked with the nnimbers 10, 20, 30, 40, 50, 60, 70, and 80, are cut in the man ner represented at W, so that they can be placed on the stalk C D. When the strength of spirits is to be measured, one of the circular weights is plaCed on C D, which is found by trial to be capable of sinking the ball so far that the surface of the liquid cuts the stem at one of the divisions between A and B. The num ber of this division is then observed, and also the temperature of the liquid ; and tha corresponding strength per cent, of the spirits is then found in a table which accompanies the instrument.
Another easy method of determining the destinies of different liquids, fre quently practised, is by means of a set of glass beads previously adjusted and numbered. Thrown into any liquid, the heavier balls sink and the lighter float at the surface ; but one of them approach ing the density of the liquid will be in a state of indifference as to buoyancy, or will float under the surface. The number on this ball indicates, in thousandth parts, the specific density of the liquid.