state, acts powerfully to oxidate and destroy the coloring particles. Dry chlorine will not bleach; it acts only FIG. 129. through the agency of water. But it is so powerful that, if the bleaching solution is not quickly removed, it corrodes and weakens the fabric. It has no action upon carbon, and therefore does not bleach printer's ink. Argentic nitrate (lunar caustic) added to a solution containing chlorine, or a soluble chloride, gives a white precipitate of argentic chloride, AgCl, which on exposure to light changes first to violet, and then to black. Combustion of Oil Argentic nitrate is the test for chlorine. of Turpentine in This element is largely used in the preparation of chloride of lime, in which form it is made available as a bleaching agent. Chlorine. 303. Hydric Chloride, HCl (Muriatic Acid). This is the only compound of chlo rine and hydrogen known. It was discovered by Priestley in 1772. It occurs in Nature among the gaseous products of volcanic eruptions. A mixture of chlorine and hydrogen gases, when exposed to direct sunlight, is converted, with violent explosion, into hydric chloride. Each of the gases also burns freely in an atmosphere of the other. If a jar be filled one half with hydrogen, FIG. 180. Direct Union of Chlorine and Hydrogen. and the other half with chlorine, and the gases ignited at the mouth, an explosion takes place; and white fumes of hydric chloride are formed. A towel should be wrapped around the jar to prevent the pieces from scattering in case of explosion (Fig. 130). Hydric chloride is generally prepared by the action of sulphuric acid on sodic chloride (common salt). The reaction is expressed by the equa tion: 2 (NaCl) +H,SO = + Na2SO, + 2 (HCl). As the gas is greedily absorbed by water, it must be collected over mercury, or by dis placement. Fig. 131 shows a convenient arrangement for its preparation. FIG. 181. Preparation of Hydric Chloride. 304. Properties and Uses.Hydric chloride is a colorless, pungent, acid gas, irrespirable, very irritating to the eyes, and extinguishes flame. It is somewhat heavier than air, having a specific gravity of 1.24. Under a pressure of 40 atmospheres at -10° C., or of 2 atmospheres at -70° C., it condenses into a colorless liquid of 1.27 specific gravity, which has never been frozen. Hydric chloride is exceedingly soluble in water, which, at 4° C., absorbs 480 times its volume of the gas. This solution is much used in the laboratory as a chemical reagent. 305. Compounds of Chlorine and Oxygen.-The compounds of chlorine and oxygen are unstable, and most of them explosive. Chlorine may act as a monad, a triad, a pentad, or a heptad, and its compounds with oxygen, together with the corresponding acids, are as follows: Chloric monoxide, Cl',O Hypochlorous acid, HCIO. 306. Chloric Monoxide, Cl,O.-This compound, also known as hypochlorous oxide, may be obtained by pass ing dry chlorine through a tube filled with mercuric oxide. A portion of the chlorine takes the place of the oxygen, forming mercuric chloride, while another portion unites with the oxygen, at the moment of its liberation, forming chloric monoxide. As a gas, its color is a shade darker than that of chlorine, and it has a similar pungent odor. It is a powerful oxidizing agent, and possesses remarkably strong bleaching power. 307. Chloric Tetroxide, Cl,O,.-When potassic chlorate, KCIO,, is made into a paste with sulphuric acid and cooled, and this paste is cautiously heated in a glass retort, over a water-bath, a deep-yellow gas is evolved, which can only be collected by displacement. Chloric tetroxide has a powerful odor, and, if heated, explodes with great violence. It may be liquefied by cold. It is absorbed by water, the solution possessing strong bleaching properties. 308. Chloric Acid, Hydric Chlorate, HCIO,.—This compound may be obtained by decomposing a solution of potassic chlorate with a solution of hydro-fluosilicic acid, the products being an insoluble potassic fluosilicate, and a dilute solution of chloric acid, which, by cautious evaporation at a low temperature, may be concentrated to the consistence of a syrup. It is a very unstable compound, being easily decomposed, especially by organic matter, which it sometimes ignites. § 2. Fluorine and its Compounds. FLUORINE.-Symbol, F. Atomic Weight, 19; Quantivalence, I.; Molecu lar Weight, 38 (?); Molecular Volume, 2 (?). 309. History. This substance does not occur in Nature, uncombined, and very little is known in regard to it. Its most frequent compound is calcic fluoride (fluor-spar), and from this it receives its name. In consequence of its great affinity for other substances, it has never been satisfactorily isolated. FIG. 132. FLUORINE 310. Hydric Fluoride, HF.-Hydric fluoride is produced when a metallic fluoride (as fluor-spar) is acted upon by hydric sulphate with the application of heat. Hydric fluoride attacks and corrodes glass, and the process must, therefore, be conducted in vessels of lead or platinum. As thus obtained it is a colorless gas, which does not condense to a liquid at -12° C. On account of its strong affinity for water, it fumes in the air, and, if inhaled, produces intense irritation of the lungs. The distinguishing characteristic of hydric fluoride is its corrosive action on glass. This may be shown by placing some powdered calcic fluoride, made into a paste with sulphuric acid, in a leaden cup (Fig. 132), and covering it with a plate of glass, previously smeared on one side with beeswax, through which characters have been traced with a fine-pointed instrument. The waxed side is placed next the mixture, and a gentle heat applied to the cup. After the lapse of half an hour, on removing the glass, and cleaning off the wax with the aid of a little oil of turpentine, the letters will be found corroded into the glass. The hydric fluoride has reacted upon and decomposed the silica of the glass at the exposed points. This quality is taken advantage of to etch the labels on glass bottles that are to be used in laboratories and drugshops, where corrosive substances abound. § 3. Bromine. Action of Fluorine. Symbol, Br. Atomic Weight, 80; Quantivalence, I., V., and VII.; Molecular Weight, 160; Molecular Volume, 2; Specific Gravity, 3.187. 311. History and Preparation. This substance was first obtained by a French chemist in 1826. The name bro mine is derived from the Greek bromos, "stench." It is not found native. After the extraction of the crystallizable salts from the sea-water, there is left a solution of the more soluble salts, called the mother-liquor or bittern. This bittern is rich in bromides, and, by heating this with manganic dioxide and hydric sulphate, chlorine is liberated from the decomposed chlorides. The chlorine, in its turn, sets free the bromine from the bromides, and the vapors are collected in a cooled receiver, where they condense into a liquid. 312. Properties and Uses.-Bromine, at ordinary temperatures, is a liquid of a deep brownish-red color. It has a peculiar, irritating, disagreeable odor. At -22° C. it solidifies to a hard, brittle, laminated mass, having a dark lead-gray color and semi-metallic lustre. At about 122° (50° C.) it boils, forming red vapors. It dissolves sparingly in water, more readily in alcohol, and in all proportions in ether. It is an active chemical agent, and a violent poison. Bromine is used in photography, and occasionally as a disinfectant. § 4. Iodine. Symbol, I. Atomic Weight, 127; Quantivalence, I., III., V., and VII.; Molecular Weight, 254; Molecular Volume, 2; Specific Gravity, 4.94. 313. History.-Iodine was discovered in 1811, in products of decomposition obtained from the mother-liquor, which remains when the ashes of sea-weed, known as "kelp," are leached, and allowed to crystallize. The name iodine is derived from the Greek ion, "violet," and refers to the color of its vapor. It is not found native. The preparation is similar to that of bromine. The mother-liquors are distilled with manganic dioxide and hydric sulphate, and the vapors condensed. 314. Properties and Uses.-Iodine is a grayish-black solid of metallic lustre, and crystallizing in forms of the tri |