or else by simple displacement, in the same manner as chlorine. It is colourless and transparent, extremely pungent, produces dense white fumes on coming in contact with the air, and reddens vegetable blues very strongly. It may be liquefied by cooling and pressure. It is rapidly absorbed by water, which, at ordinary temperatures, takes up 480 times its volume of the gas. The solution is called liquid or aqueous hydrochloric acid; it was formerly called muriatic acid, and spirit of salt. The properties of aqueous hydrochloric acid are similar to those of the gas. The most convenient mode of preparing it is to pass the gas into water by means of the apparatus represented in Fig. 19. The A Fig. 19. gas is generated in the flask A, and before passing into the water in the vessel C, in which it is to be condensed, it is made to pass through the wash-bottle, B, in order that any solid or liquid matter from the flask, which might be mechanically carried over with the gas, may be arrested, and prevented from passing into the solution in C. The wash-bottle is filled to the depth of an inch or two with oil of vitriol, or with strong hydrochloric acid prepared by a previous operation; pure water would absorb a large quantity of the gas, and occasion waste. The figure will give a sufficient idea of the arrangement, without further description. The vessel c should be kept cool by immersion in a jar of cold water, because the absorption produces great heat, and the solution, when hot, gives up the gas again. A saturated solution of hydrochloric acid has a specific gravity of 121, and contains 42-43 per cent. of the gas. In this state it is strongly acid, and emits dense white fumes on exposure to the air. It blisters the skin, and must therefore be used with caution. It mixes with water in all proportions, the specific gravity of the solution diminishing with its strength. The strong acid, when subjected to distil lation, gives off more acid than water, till its specific gravity is reduced to 1.094, and its strength to about 18 per cent. of reai acid; in this state it boils at 230° Fahr., and distils over, unaltered in strength. The acid, when pure, evaporates without leaving any residue. Metallic Chlorides.-Some of these compounds may be formed by the direct union of chlorine with the respective metals. Thus, potassium, when introduced into chlorine gas at ordinary temperatures, takes fire, and is converted into a chloride. So, likewise, do arsenic and antimony in the state of fine powder, and copper in the form of thin leaf; other metals, viz. sodium, zinc, iron, and mercury, likewise burn in the gas, but not unless they are previously heated; lead, silver, and gold, also unite directly with chlorine, but without visible combustion.-But the most general mode of forming metallic chlorides is by the action of hydrochloric acid, either on the metal or its oxide. Zinc decomposes hydrochloric acid, taking the chlorine to itself, and liberating the hydrogen. The solution then contains chloride of zinc-a compound of 32-5 parts of zinc with 35′5 of chlorine; the action therefore consists in the substitution of 32.5 parts of zine for 1 part of hydrogen. A similar action is exerted by iron, tin, potassium, sodium, and one or two other metals. Most metallic oxides dissolve in hydrochloric acid, and the solution, when evaporated, leaves a solid chloride of the metal: thus, soda dissolves in the acid, and yields common salt, which, when dry, is a chloride of sodium. The change which here occurs, consists in the chlorine combining with the sodium, and the oxygen with hydrogen; in other words, the sodium and hydrogen change places, as represented in the fol lowing diagram, which the student is now HYDROCHLORIC ACID. Chlorine SODA. Sodium Oxygen Compounds of Chlorine and Oxygen. Chlorine and oxygen form five definite compounds, the names and composition of Chloride of sodium. which are as follows: Water. ......... ...... ice or immersed in cold water. Part of the chlorine then combines with the mercury, and the rest with the oxygen, forming hypochlorous acid. The gas may be collected either over mercury or by displacement; it cannot, however, be kept over mercury, as it acts rapidly on that metal. Hypochlorous acid is a gas of a deep yellow colour inclining to red; its odour resembles that of chlorine, but is less suffocating. It is three times as heavy as atmospheric air. By pressure, or by cold of 4° Fahr. it may be condensed into a deep orange-coloured liquid. By a heat even short of that of boiling water, it is decomposed with explosion, two volumes of the gas being resolved into two volumes of chlorine and one volume of oxygen, so that its elements when united, occupy less space by one-third than they do when separate. It sometimes explodes even by the heat of the hand in transferring it from one vessel to another; great care must therefore be taken in experimenting with it. Water absorbs more than 100 times its volume of hypochlorous acid; the solution has the colour and odour of the gas, and bleaches powerfully. Oxide of Chlorine 35.5 32 2 4+ Chloric Acid Similar actions are exerted by the oxides of 35540 2... 5 potassium, calcium, iron, manganese, zinc, Perchloric Acid 355562 7 copper, &c., all these metals forming chlo- 1. Hypochlorous Acid.-This compound rides which are soluble in water. Silver is, under ordinary circumstances, a gas. It forms an insoluble chloride. Take a solu- may be obtained pure by passing dry chlotion of nitrate of silver (the salt commonly rine over finely divided red oxide of mercalled lunar caustic, from its use in sur-cury,† contained in a tube surrounded with gery), and add to it a few drops of hydrochloric acid, or solution of common salt. You will see a white, curdy substance separate from the liquid. This substance is the chloride of silver; its insolubility in water causes it to separate from the solution and assume the solid form, as soon as the chlorine in the one liquid comes in contact with the silver in the other. So very insoluble is this compound, that chlorine and silver will detect each other's presence in solutions of the most extreme degree of dilution. A solution of common salt so dilute as to contain only one part of chlorine in 1,600,000 parts of water, still exhibits a perceptible cloudiness on the addition of a drop of nitrate of silver. A solid substance separated from a liquid in this manner is called a precipitate, being, as it were, thrown down from the liquid. The study of the formation and character of precipitates constitutes a most important feature in analytical chemistry, being, in fact, the principal means to which we have recourse, when we wish to ascertain the presence of a substance in solution. Lead forms with chlorine a compound which is not quite insoluble, but sparingly scluble in water, requiring, indeed, 135 parts of cold water to dissolve it. Hence hydrochloric acid, or a soluble metallic chloride, forms a precipitate with lead-solutions, provided the latter are not very dilute. Mercury forms two chlorides, one soluble in water, and containing 100 parts of inercury united with 35 5 of chlorine; the other insoluble, and containing 200 parts mercury with 35.5 chlorine. The latter is the wellknown substance, calomel; the former is corrosive sublimate. Hypochlorous acid forms salts called Hypochlorites. These are obtained, mixed with chlorides, by the action of chlorine on their several bases in the state of solution or suspension in water. Thus, when * The prefix hypo (meaning under) attached to the name of this acid, is intended to denote that it contains less oxygen than chlorous acid. The oxide of mercury used in this process must be prepared by precipitating a solution of corrosive sublimate with caustic potash; the ordinary crystalline red oxide is not acted upon by chlorine. chlorine gas is passed through a solution | gent odour. This gas is chlorous acid. Its of potash (oxide of potassium), that sub-specific gravity is 2646; it bleaches litmus stance is decomposed, the potassium com- paper and solution of indigo. By intense bining with part of the chlorine in the form cold it may be condensed into a reddish of chloride of potassium, while the rest liquid. When heated to 135°, it explodes, of the chlorine unites with the oxygen of though not so violently as hypochlorous the potash, producing hypochlorous acid; | acid, 3 measures of it expanding by deand this, with the undecomposed portion composition to 5 measures, of which two of potash, forms hypochlorite of potas- consist of chlorine and three of oxygen. sium. The solution must be kept cold, It is soluble in water, forming a yellow otherwise the hypochlorite will be decom- solution which bleaches indigo. Its salts posed, and other compounds formed. The are called Chlorites. solution thus obtained has the peculiar odour of hypochlorous acid, and bleaches strongly. A similar compound may be obtained by treating soda with chlorine. But the most useful of this class of salts is the bleaching powder, commonly, but incorrectly, called chloride of lime. This substance, which is really a mixture of chloride of calcium (the metal whose oxide is lime) and hypochlorite of calcium, is prepared in very large quantities by exposing slaked lime slightly moistened with water to the action of chlorine gas. The compound thereby produced is a loose white powder, soluble in water, and having the peculiar smell of hypochlorous acid. It is, in fact, decomposed by the carbonic acid of the air, carbonate of calcium being formed, and hypochlorous acid evolved. Weak hydrochloric or sulphuric acid decomposes it still more quickly. This substance is extensively used for bleaching, the articles to be bleached being dipped into a weak solution of it, and then transferred to a vat containing dilute sulphuric acid, whereby the hypochlorous acid is set free, and enabled to exert its bleaching power. It is also, as well as the corresponding potash and soda compounds, extremely useful as a disinfecting agent, since hypochlorous acid decomposes organic compounds quite as readily as chlorine. For this purpose, the solution is exposed in shallow vessels, or cloths steeped in it are suspended in the apartment, so that the carbonic acid of the air may act slowly on the compound and liberate the hypochlorous acid. 2. Chlorous Acid.-When chlorate of potassium is gently heated with moderately strong nitric acid and some substance which takes up oxygen readily, such as sugar or tartaric acid, a dark greenishyellow gas is evolved, having a strong pun 3. Oxide of Chlorine.-This compound is also a gas of a deep yellow colour, and is reduced to the liquid state by exposure to the cold produced by a mixture of ice. and salt. The gas is obtained by the action of strong sulphuric acid on chlorate of potassium. If you put a small quantity of this salt into a glass tube, pour sulphuric acid upon it, and gently heat the tube for a few seconds over a lamp—a series of loud detonations will ensue, and the tube will be filled with a yellow gas, having a pungent, irritating odour, something like that of chlorine, but having likewise an aromatic quality. Its specific gravity is 2:34. Water absorbs 7 times its volume of oxide of chlorine; mercury likewise absorbs it rapidly. Being, however, a heavy gas, it may be collected by displacement like chlorine; but I would not recommend you to try the experiment, as the gas is very dangerous, exploding violently when moderately heated. Two volumes of it are thereby resolved into one volume of chlorine and two of oxygen. The facility with which this compound decomposes, may be safely and pleasingly exhibited by the following experiments :-Place some crystals of chlorate of potassium and a few small pieces of phosphorus, at the bottom of a wine-glass filled with water, and pour a little strong sulphuric acid on them through a glass tube or a long funnel reaching to the bottom of the water. The phosphorus will immediately take fire, and burn with a series of slight detonations, thus exhibiting the curious phenomenon of combustion under water. The effect is due to the combination of the phosphorus with the chlorine and oxygen, into which the oxide of chlorine is resolved at the moment of its liberation. A similar effect may be produced as follows:-Take a small quantity of chlorate of potassium and about twice as much lump-sugar; pound them separately; mix them together with the blade of a knife (rubbing them together in a mortar might produce a dangerous explosion), and let fall on the mixture a drop of sulphuric acid; it will immediately take fire and burn with great rapidity. phur are rubbed together in a mortar, a series of oud, sharp detonations is produced. A mixture of this salt with phosphorus explodes with great violence when struck with a hammer; but the experiment is dangerous. Lucifer matches, which take fire by friction, are tipped with a mixture of chlorate of potassium and some combustible matter, such as sulphur, sulphide of antimony, finely pounded charcoal, &c. 4. Chloric Acid.-This compound may be obtained in the state of aqueous solution, by dissolving chlorate of barium (the preparation of which will be presently When a mixture of chlorate of potassium described) in water, and adding sulphuric and hydrochloric acid is gently heated, a acid; sulphate of barium is then separated yellow gas (formerly called Euchlorine) is in the form of an insoluble powder, and given off, which, when exposed to a temchloric acid remains in solution. The perature of 0° Fahr., condenses to a red liquid may be decanted after the precipi-liquid. This liquid is Chloro-chloric acid, tate has settled down, and concentrated by a compound of chloric and chlorous acids, evaporation under the exhausted receiver containing 106 5 parts of chlorine and of an air-pump, a shallow vessel containing 104 parts of oxygen. The yellow gas oil of vitriol being placed beneath the is a mixture of this compound with free chloric acid, to absorb the aqueous vapour chlorine. as fast as it is evolved. The acid, when highly concentrated, is of a syrupy consistence, and is so prone to decompose and give up its oxygen, that it sets fire to paper. A dilute solution reddens litmus paper in the first instance, but afterwards bleaches it, or removes its colour altogether.. 5. Perchloric Acid.-We have seen that chlorate of potassium, when heated, is resolved into oxygen and chloride of potassium. The whole of the oxygen does not, however, go off at once, but part of it unites with the undecomposed portion of the chloric acid, converting it into perchloric acid. The name of the latter acid is intended to denote that it contains more oxygen than the former. If the process be stopped at a certain point, a considerable quantity of perchlorate of potassium remains mixed with the chloride, and being much less soluble in water, may be easily separated by solution and crystallization. When perohlorate of potassium is distilled with dilute sulphuric acid, the perchloric acid passes off, and condenses in the form of an aqueous solution. This solution is colourless, and fumes in the air when strong. In its state of greatest concentration, it has a specific gravity of 165. It is much less liable to decompose than chloric acid. The perchlorates resemble the chlorates in most respects, but they are more stable. When strongly heated, they give off all their oxygen, and are reduced to chlorides. All the salts of chloric acid are soluble in water. The most important of them is the chlorate of potassium (more commonly called chlorate of potash). This salt is obtained, mixed with chloride of potassium, by passing chlorine gas through a hot solution of potash. On subsequently evaporating the liquid, the chlorate, which is the less soluble of the two salts, crystallizes out first, in thin colourless plates. In a similar manner, the chlorates of sodium and of barium may be obtained by passing chlorine through solutions of soda and baryta (oxide of barium). All chlorates when heated, give up the whole of their Oxygen, and are converted into chlorides. Thus, chlorate of potassium, when heated to redness, yields a large quantity of oxygen gas, and a residue of chloride of potassium. This tendency to give off oxygen is, in fact, the distinguishing characteristics of chloric acid and its salts. Perchloric acid forms with chlorous consequence of this, when a chlorate is acid, a compound called Chloro-perchloric mixed with combustible matter, and the acid, containing 1065 parts of chlorine mixture heated, struck, or rubbed, violent and 136 parts of oxygen. It is a redcombustion and detonation are often pro-dish brown liquid, obtained by the action. duced. Thus, when small quantities of of light on perfectly dry chlorous acid chlorate of potassium and flowers of sul- gas. In was styled by the emperor Julian, who was surnamed the Apostate; or, as the Orientals call it, "a pearl surrounded by emeralds," one of the gates of the Caaba," and "Mohammed's heel," from being the rendezvous for all the pilgrims from the north of Asia-is probably the most ancient city in the world; and, notwithstanding the vicissitudes it has experienced, is still the most thoroughly oriental city in the East, and has undergone fewer changes, though torn by civil war and attacked by foreign powers. The city is supposed to have been founded by Uz, the son of Shem, the third son of Noah. In the days of Abraham it was a celebrated city, and we find that his confidential servant, Eliezer, was a native of it. Damascus is a more ancient name than the Arabic one of El Sham, and is derived from Damasck, which is said to have been derived from two Syriac words-dam (blood), and sakh (innocent), which allude to the tradition that Cain slew his brother Abel on this spot. The devout Christians ascribe the almost unchanged and prosperous state of the city to the protective agency of the innocent blood of Abel, |