Hypochlorous acid, CIO, is a yellow gas, has very powerful bleaching properties, and may be prepared by adding the powdered red oxide of mercury to a bottle of chlorine containing a little water. The bottle should be briskly shaken for a few moments. The oxygen of the mercury combines with the chlorine to form CIO, which dissolves in the water, and forms a compound called the oxychloride of mercury; thus 2HgO +2C1 = HgCl,HgO + CIO. Chlorous acid, CIO,.-This compound is very difficult of preparation, and not very important. Hypochloric acid, ClO4, sometimes called the peroxide of chlorine. This acid may be prepared by carefully mixing concentrated sulphuric acid and the chlorate of potash into a thick paste. After it has cooled it should be cautiously introduced into a green glass retort, and very slowly heated by placing the retort in water; and, gently raising the temperature of the water by a lamp or other source of heat, a green-yellow gas comes off, which is hypochloric acid, ClO4. It must be collected by displacement, as it is very soluble in water, and mercury decomposes it. This compound is very explosive. At a temperature below boiling water it is resolved with great violence into oxygen and chlorine; hence the care required in its preparation. Decomposition: 3(KO,CIO5)+3(HO,SO2)=2C1O4+C1O7+ If a mixture of chlorate of potash and loaf sugar be placed on a plate and touched with a glass rod previously dipped in sulphuric acid, it is instantly set on fire. In this experiment the hypochloric acid, C104, is disengaged with such violence as to cause combustion. If half a teaspoonful of chlorate of potash and a few chips of phosphorus be placed in a deep test or ale glass nearly filled with water, and a little sulphuric acid by a small funnel which reaches to the bottom of the glass, the phosphorus will burn under water from the oxygen of the disengaged hypochloric acid. Chloric acid, CIO5, forms in combination with bases salts of considerable importance, especially the chlorate of potash. If a current of chlorine be sent through a moderately warm solution of caustic potash, and the liquid, when saturated with the gas, concentrated by evaporation, crystals of chlorate of potash are obtained. In this reaction a part of the potash, KO, is decomposed to form chloric acid and the chloride of potash: 6KO + 6C1 = KO,CIO5 + 5KC1. From the chlorate of potash chloric acid is obtained, by boiling with a solution of hydrofluosilicic acid. The process is tedious, and requires care. Perchloric acid, CIO,, is obtained from the perchlorate of potash, KO, CIO,. The chlorates in solution give no precipitate with the nitrate of silver. When heated they evolve oxygen; and if treated with sulphuric acid they evolve the characteristic yellow gas as mentioned under hypochloric acid. BROMINE. Symbol, Br; Equivalent, 78.26. This element is found in sea-water at ordinary. temperatures. It is a brownish red liquid, having a disagreeable odour, closely resembling chlorine and iodine in character. It is found in combination with magnesium in sea water, as the bromide of magnesium, MgBr. It is obtained by agitating ether with any solution of bromine. After the less soluble salts have been separated, a stream of chlorine is then sent through the solution, which decomposes the bromide of magnesium, the ether dissolving the liberated bromine. The liquid is transferred to a retort with a receiver, and heat applied, when the bromine condenses in the cold part of the retort and receiver. Bromine, when associated with water has bleaching properties. Hydrobromic acid, HBr, is analogous to hydriodic acid, and has nearly the same properties, and may be prepared by substituting bromine for iodine, in the preparation of hydriodic acid. There is only one known oxide of bromine, bromic acid, BrO,, which is prepared by adding bromine to a solution of caustic potash, until all alkaline properties are destroyed. The change is the same as that described under chloric acid. IODINE. Symbol, I; Combining Equivalent, 127. It is At ordinary temperatures, iodine is a bluish-black, metallic looking substance, having the appearance of scales of black lead. It occurs chiefly in combination with sodium and potassium in sea water. It is a constituent of marine plants and animals. chiefly prepared from the ashes of sea weeds, called kelp. The ashes are mixed with water, filtered and evaporated, until the solution is reduced to a very small quantity: the salts of sodium, potassium, and magnesia being removed as they crystallise. The mother liquor left after the removal of these salts, contains the iodine in combination with magnesia and iodine. This is placed in a leaden retort with sulphuric acid and the binoxide of manganese. On the application of heat the iodine distils over as a dark purple vapour, which is condensed. This process may be imitated by placing in a retort connected with a receiver, a solution of the iodide of potassium, a little powdered binoxide of manganese, and sulphuric acid: on the application of heat, a beautiful violet vapour passes over, which condenses in the cold part of the retort and receiver in small shining scales. Decomposition : KI + MnO2 + 2HO,SO, = HO,SO, + MnO,SO ̧ + HO+ I. Iodine stains the skin; it acts violently on the animal system, and is used in medicine. When iodine is free, it produces a splendid blue colour in contact with starch. If any soluble iodide be first liberated with a little chlorine water, it is then capable of producing the characteristic colour with starch. Iodine forms with oxygen two acids, iodic acid, IO5, and periodic acid, IO. 59 In combination with hydrogen it forms an acid known as hydriodic acid, HI. This acid is a gas, but it may be obtained in solution by passing sulphuretted hydrogen through water in which powdered iodine is suspended. In this case, the sulphur of the sulphuretted hydrogen is liberated, and the hydrogen combines with the iodine, forming hydriodic acid, HS + I = HI + S. The liquid is warmed, filtered, and a colourless solution of the acid is obtained, which soon becomes of a brown colour on exposure to air, by its decomposition into free iodine and water, HI + 0 = HO + I. Iodine dissolves freely in alcohol. If a polished silver plate be held over the vapour of iodine, it first becomes yellow, then violet, and then a deep blue, owing to a combination of the iodine with the silver. The iodide of silver thus formed is decomposed by light. FLUORINE. Symbol, F; Equivalent, 18·70. Owing to the powerful affinities of this element for the metals, also for silicon and hydrogen, it has never been isolated. Its most frequent combination is with calcium, as the fluoride of calcium, CaF, or fluor-spar. It exists, also, in a state of combination, in the bones and teeth of animals. So far as it has been examined, it is said to be a gas, like chlorine. There is no known oxygen compound of fluorine, but in combination with hydrogen, it forms an acid known as hydrofluoric acid, HF. To obtain this compound, the powdered fluoride of calcium is heated with concentrated sulphuric acid in a platinum or lead retort connected with a receiver of the same metal. Kept cool by being surrounded with a freezing mixture, a volatile, colourless liquid, is obtained, which emits suffocating white fumes in the air. It unites with water, and very dilute solutions attack glass. It has, therefore, to be kept in leaden, or gutta-percha bottles. The decomposition is easily explained: CaF, HO,SO, = HF + CaO,SO3. If the concentrated acid be dropped upon the skin, it occasions ulcers of a very malignant and |