very existence of animal life. The prime equivalent of carbonic acid is 2.75, and carbonic acid is composed of carbon 0.75 + 2.0 oxygen. Carbonic acid may be decomposed when combined with a base, as lime, by phosphorus and heat, for charcoal and a phosphate of lime will be produced. But carbonic acid in the state of gas may be decomposed by potassium. Five grains of potassium will decompose three cubic inches of gas, and be converted into potassa, producing at the same time three-eighths of a grain of charcoal. If passed over a coil of fine iron wire heated to redness, in a porcelain tube, and the operation repeated, the iron will be oxidized, and the carbonic acid changed into carbonic oxide gas. Charcoal will not burn in dry chlorine. It unites with a less proportion of oxygen, and forms carbonic oxide gas, which burns with a deep blue flame. This combination is formed by distilling in a red heat, a mixture of equal parts of iron filings and chalk. This gas mixed with chlorine gas, and exposed to the sun's rays, will unite with it, and form chlorocarbonic acid gas. Carbon unites with azote, and forms cyanogen, the base of Prussic acid. It unites likewise with hydrogen in two proportions, forming the hydroguret and the bihydroguret of carbon, both of which are carburetted hydrogen gases. The former is obtained by distilling a mixture of four parts of sulphuric acid, and one of alcohol. The gas is very inflammable, and burns with great splendour; and on that account may be used for exhibition, in an apparatus similar to that of Cartwright. (See _Fire-works with Inflammable air_.) It was called by the German chemists olefiant gas. The other species, called also the light carburetted hydrogen gas, may be obtained by agitating the mud at the bottom of stagnant pools; and by the distillation of moist charcoal, wood, pitcoal, pitch, or almost any animal or vegetable substance. The gas, used for _gas-lights_, is the same. It is usually obtained from pit coal. We may merely observe, that the gas used for that purpose, _i. e._ for illuminating streets, theatres, manufactures, &c. as obtained in the common method, is not altogether the bihydroguret of carbon; but, according to the experiments of Dr. Henry, a mixture of that gas with the hydroguret, and occasionally carbonic oxide. Carbon enters into other combinations. It exists as a component part of gums, resins, sugar-starch, and other vegetable products, as the vegetable acids, its union with iron forms steel, a substance greatly used in the preparation of some fire-works, especially in some of the _rains_ and _stars_, and in the composition of _brilliant fire_. (See _Iron_.) As charcoal enters into the composition of gunpowder, and the effective force of powder depends considerably on the quality, as well as the proportion of charcoal, it is obvious for this purpose, it should be as pure as possible.