two of sulphur. Without action on vegetable colours, insoluble in water, but very soluble in alcohol. It burns, giving rise to sulphurous and carbonic acids. It forms a detonating mixture with oxygen when inflamed. Bisulphide of carbon is somewhat analogous to carbonic acid. Uses.-Vulcanizing indiarubber and gutta percha, and killing moths. LIGHT CARBURETTED HYDROGEN. Symbol, C2H.; Equivalent, 16. Known as inflammable air, marsh gas, fire-damp. Physical Properties. Permanently gaseous, without colour, but having a disagreeable odour. Specific Gravity.-0.556. Chemical Properties. It is composed of two equivalents of carbon and four of hydrogen, neutral in its action upon vegetable colours, and insoluble in water. It is not a supporter of combustion or respiration. It is combustible; when mixed with common air it detonates violently, forming carbonic acid and water. Preparation. Sixty parts of quicklime, forty parts of solid caustic potash, and forty parts of the crystallized acetate of soda, are strongly heated together in a retort. The reaction consists in the conversion of acetic acid by the elements of water into carbonic acid and light carburetted hydrogen. The affinity of potash for carbonic acid is the determining cause. The lime merely prevents the potash from fusing and attacking the glass. HEAVY CARBURETTED HYDROGEN. Sometimes called olefiant gas. Physical Properties.-At ordinary temperatures a gas, but not permanently gaseous. It is without colour, and has the odour of ether. Specific Gravity.-0.978. Chemical Properties. It is composed of four equivalents of carbon and four of hydrogen. Neutral to testpaper, and insoluble in water. Mixed with air, it forms an explosive compound. When inflamed, it forms carbonic acid and water. It is decomposed at a high temperature. It is not a supporter of combustion or respiration. When mixed in equal volumes with chlorine an oily liquid is formed-Dutch oil. If the chlorine be in excess and a light applied, there is an abundant deposit of carbon. Preparation. By heating in a flask one part by measure of alcohol, CHO2, and three parts of sulphuric acid, SO,,HO. Decomposition: C,H,O + SO,HO = SOHO + 2HO+CH.. COAL-GAS. Obtained by the distillation of coal in iron retorts. It is a mixture of light carburetted hydrogen, heavy carburetted hydrogen, carbonic oxide, hydrogen, and other volatile products. The clearness of the light is owing to the presence of solid particles of carbon raised to white heat. SILICON. SILICIC ACID. Symbol, SiO,; Equivalent, 45'3. Physical Properties.—A solid crystalline body, found in nature as quartz, agate, silex, flint, and sand. It is very refractory, scarcely yielding to the heat of the oxyhydrogen blowpipe. Chemical Properties.-Composed of one of silicon to three of oxygen. It is insoluble in water and acids. Silicic acid unites with bases, forming silicates. It is decomposed by hydrofluoric acid. Its uses in the arts are numerous. Artificial Silicates.-Earthenware, glass, porcelain, &c. HYDROGEN. Symbol, H; Equivalent, 1. Discovered by Cavendish in 1777, and called inflammable air. Physical Properties.-Permanently gaseous, without colour, odour, or taste. Density, o'069. Chemical Properties.-Simple body, slightly soluble in water. Has a great affinity for oxygen, and forms with that gas an explosive mixture, which detonates violently on the application of a light. It is combustible, but not a supporter of either combustion or respiration. It does not combine directly with nitrogen to form ammonia. Preparation. 1st method. Decomposition of cold water by zinc or iron in the presence of sulphuric acid :— Zn+SO,,HO = ZnO,SO; + H, 2nd method. By passing steam through a gun barrel, loosely filled with iron turnings, and raised to a red heat 4HO+3Fe FeO. + 4H. = The * Uses.-Formerly employed to inflate balloons. oxyhydrogen light of Drummond. The oxyhydrogen blowpipe. PROTOXIDE OF HYDROGEN-WATER. Physical Properties.—A compound body, liquid at the common pressure and temperature. At 32° Fahr. it solidifies into ice. At 212° Fahr. it boils. It evaporates at all temperatures. Water is without colour, but in large masses it appears of a blue colour. It is without taste or smell. Chemical Properties.-Composed, by weight, of 1 ot hydrogen to 8 of oxygen; by volume, 2 of hydrogen to I of oxygen. The composition of water was discovered by Cavendish and Nicholson in 1800. The exact quantitative composition of water was determined by Gay-Lussac and Humboldt. Analysis of Water.-1st method. By the decomposition of steam when passed through a red-hot porcelain tube filled with copper turnings. 2nd method. The decomposition of water by voltaic electricity. Water is a solvent for most substances. The purification of water is effected by distillation; such water is called distilled water, and is extensively used in the laboratory. The uses of water are almost innumerable. 97 METALS. POTASSIUM. Symbol, K; Equivalent, 39. THIS metal was discovered by Sir H. Davy, in 1807, by exposing the hydrate of potash, KO,HO (KHO,), to the action of a powerful voltaic battery between two plates of platinum. Potassium occurs in nature in combination with silicic acid, SiO, in granite, trap, basalt, and other igneous rocks. These rocks crumble down by the action of the atmosphere, and the potash finds its way into the soil. Soils destitute of potash are uniformly barren. It is worthy of remark here, that the leaves and young parts of plants contain the most potash, while the trunks of trees contain scarcely any. Potassium in combination occurs in most natural waters, and in the sea as the bromide of potassium, KBr, the iodide of potassium, KI, and the chloride of potassium, KCl. Potassium is prepared in the following manner :— -A mixture of the carbonate of potash, KO,CO,, and powdered charcoal is prepared, and thoroughly dried in a covered iron pot. When quite cold it is reduced to powder, and mixed with of its weight of charcoal, in small lumps. The mixture is then transferred to a well-hammered iron retort, or a bottle in which mercury is imported. The retort is placed in a furnace and the fire supplied with dry wood, so that the retort is enveloped in flame and kept at a uniform heat, approaching to whiteness. A copper receiver is divided by a partition, into one portion of which a tolerably large pipe from the retort dips into naphtha. The other side of the receiver is filled with ice. The fire is now raised in temperature, when decomposition of the carbonate of potash, KO,CO2, by the charcoal takes place, K |