of the latter in the dark. Ozone may be detected in the bottle within a minute after the introduction of the phosphorus; if allowed to stand for six or eight hours, the air in the bottle will be abundantly charged with it. The phosphorus should then be removed, and the air freed from phosphorous acid by agitating some water in the bottle. Properties.-The ozone thus obtained (in admixture with air) has the following properties: it is a colorless gas, possessing a very peculiar odor, which, when concentrated, much resembles that of chlorine, but when diluted is precisely the odor observed when an electric machine is in action. When air has been powerfully charged with ozone, it can be inspired with difficulty; it acts powerfully on the mucous membranes, producing very disagreeable sensations; small animals immersed in it soon cease to exist. Pure ozone must therefore be highly poisonous. Ozone is insoluble in water; it possesses powerful bleaching properties, and also acts as an energetic oxidizing agent, transforming phosphorus into phosphoric acid, and powerfully oxidizing many metals, converting them and their lower oxides into the highest oxides they are capable of forming. Thus, lead and silver are converted into oxides, antimony and arsenic into arsenic acid and antimonic acid; the salts of the protoxides of manganese, cobalt, nickel, are decomposed by it, the acids being evolved and the binoxides formed. It also decomposes many hydrogen-acids (e. g. hydrosulphuric acid), and oxidizes. organic compounds. It combines with chlorine, bromine, and iodine, and is in many respects analogous in its action to the binoxide of hydrogen. Two views are entertained respecting the constitution of this body; the one, that it is oxygen in an allotropic condition-the other, that it is a compound of oxygen similar to binoxide of hydrogen. The former is the view which possesses the greater number of supporters, particularly since it has been proved that, on passing dry ozonized air through a redhot tube, the destruction of ozone by the heat (it being only capable of forming at ordinary temperatures) is unaccompanied by the production of any water. Many organic compounds, such as ether and turpentine, when exposed to the action of air and light, undergo peculiar changes, and acquire very powerful bleaching and oxidizing properties, apparently by association with ozone. Tests for Ozone.-The most delicate test for the presence of ozone is prepared in the following manner: one part of pure iodide of potassium and ten parts of starch are boiled together, for a few moments, with two hundred parts of water, and white filtering-paper is saturated with the liquid thus obtained. Such paper is immediately turned blue when introduced moist into ozonized air. If introduced dry it will remain colorless, but becomes blue immediately upon being moistened. Paper prepared with a solution of sulphate of manganese is also a good test for ozone, becoming rapidly brown from formation of binoxide when introduced into ozonized air. 1 By very recent researches, Baumert believes that he has shown the ozone obtained in the electrolysis of water to consist of a teroxide of hydrogen. He passed the perfectly dry ozone, first through a tube containing anhydrous phosphoric acid, which was unaffected by it, then through a tube heated to redness, and lastly, through a second tube, containing phosphoric acid, which indicated the presence of moisture produced in the decomposition of the ozone. The proportion of oxygen was determined by passing the ozone into a standard solution of iodide of potassium. HYDROGEN.1 Sym. H. Eq. 1. Sp. Gr. 0.0692. § 73. HYDROGEN was discovered by Cavendish, in 1766. It constitutes 11 per cent. by weight of water; it also occupies an important place in the composition of nearly all organic substances. Preparation.-Hydrogen may be prepared : I. By passing the vapor of water through an iron tube filled with iron nails, and heated to redness: Fe,+4HO=Fe,O,+H. II. By adding dilute sulphuric acid (or hydrochloric acid) to granulated zinc (or fragments of iron), covered with water, in a Woulfe's (or common widemouthed) bottle provided with a funnel-tube and delivery-tube (§ 27):— Zn+HO.SO, ZnO.SO,+H. The gas may be collected over water (§ 29) or by upward displacement (§ 31):III. By decomposing water with potassium or sodium, in a small jar filled with mercury, and standing over the mercurial trough: K+HO=KO+H. IV. By heating zinc or iron with solution of potassa, when the oxygen of the water is abstracted by the metal. In experiments with hydrogen, the operator must allow the gas to be evolved for two or three minutes without attempting to collect it, so that all the atmospheric air may be expelled from the apparatus, since the neglect of this precaution may be attended with danger from the formation of an explosive mixture. The hydrogen prepared with commercial zinc or iron is never pure. It has a nauseous odor due to a peculiar compound of hydrogen with carbon derived from the metal; small quantities of sulphur and arsenic are also obtained from the same source, and pass off in combination with hydrogen (arsenic is also sometimes derived from the oil of vitriol). In order to purify this gas, it should be passed first through solution of potassa; secondly, through solution of nitrate of silver, and lastly, if the gas be required free from aqueous vapor, through a bent tube containing pumice-stone moistened with oil of vitriol, or through a wash bottle, containing this liquid (§ 28). It is difficult to dry hydrogen perfectly, on account of its high diffusive power (§ 22). 74. Properties.-Hydrogen is a permanent gas, colorless, and, if quite pure, inodorous. Its solubility in water is somewhat less than that of oxygen. This gas is the lightest substance known; its lightness may be readily shown by pouring it upwards from one jar into another, each jar being afterwards presented to the flame. Hydrogen is a very inflammable gas; if a lighted taper be thrust up into an inverted jar of hydrogen, the taper is extinguished, but the gas takes fire at the mouth of the jar, and burns with a pale bluish flame. If hydrogen, dried by means of chloride of calcium, be burnt at a glass jet (§ 32), and a dry jar held over the flame, the water which is produced in the combustion will be observed to condense upon the glass. The flame of hydrogen, though very faintly luminous, has a very high tempe rature. If a jet of hydrogen be burnt in a long wide glass tube, open at both ends, the vibrations, caused by the alternate extinction and rekindling of the flame, succeed each other so rapidly as to produce a musical tone. 1 dop, water, yowán, I produce. The diffusive power (§ 22) of hydrogen is exceedingly high, whence it can be preserved only in vessels which are very tightly closed with stoppers. Binoxide of Hydrogen, HO, WATER, HO. Eq. 9. Sp. Gr. 1. § 75. A mixture of two volumes of hydrogen and one volume of oxygen explodes, when brought in contact with flame, when suddenly and powerfully compressed, or when an electric spark is passed through it, producing water, which, in the state of vapor, at 60° F. and 30 inches bar. would occupy two volumes. On introducing spongy platinum or finely divided platinum (platinum-black) into a mixture of the gases, it is instantly exploded. Or, if a jet of hydrogen be allowed to impinge upon a ball of spongy platinum in the air, the metal will become redhot, and the hydrogen will be immediately afterwards ignited. Faraday has shown that the union of the two gases may be even effected by a perfectly clean surface of rolled platinum. This remarkable property of platinum1 led Döbereiner to the construction of his beautiful little apparatus for the production of instantaneous light. Various opinions are entertained respecting the manner in which spongy platinum acts in effecting the combination of hydrogen with oxygen. Platinum, in a finely divided state, has been found to possess the remarkable property of condensing in its pores about 253 times its volume of oxygen, whereby the latter must be rendered even denser than water. It has been supposed that hydrogen, coming in contact with oxygen in this highly condensed state, combines with it immediately. Another view taken by some chemists of this phenomenon is based upon the supposition that when finelydivided platinum is exposed to air or oxygen, it becomes covered, even at the common temperature, with a very minute coating of oxide, which is reduced to metal again by hydrogen, even in the cold. It is therefore supposed that, when the oxygen of the air and a jet of hydrogen are allowed to act upon spongy platinum, a series of continuous oxidations and reductions takes place, accompanied by a rise in temperature sufficient to heat the platinum to redness, and thereby to set fire to the hydrogen. A mixture of hydrogen and oxygen in proper proportions may also be exploded in an eudiometer, by the electric spark (§ 32). They then combine with a sudden flash, and without noise, water being produced. The combination of hydrogen and oxygen is accompanied by the disengagement of the most intense heat that can be produced. If the mixed gases are allowed to issue under some pressure from a narrow jet, and inflamed, the heat disengaged by the combustion is sufficiently powerful to melt platinum and pipeclay, which substances resist the heat of all furnaces. The flame of this jet of mixed gases (generally termed the oxyhydrogen-blowpipe jet) is very pale, but becomes dazzling the moment a solid infusible substance is introduced into it. Thus, if the flame be allowed to fall upon a disk of lime, a star of most intense light is obtained, which is generally known by the name of the Drummond or lime-light. This phenomenon is owing to the state of intense incandescence of the particles of lime when exposed to the heat of the oxyhydrogen flame. Various forms of apparatus have been contrived to supply the jet with the mixed gases. Other substances besides platinum, such as gold, palladium, and even some stones and glass, possess this property to some extent, requiring, however, the aid of heat to effect the combination. The safest are those in which the gases are retained in separate reservoirs, and only allowed to mix in small quantities, just as they are to be burnt, that portion of the apparatus between the jet and the chamber in which the mixture is effected being stuffed with very thin brass wires, by which means, owing to the conducting power of the metal, the temperature is so far reduced that all danger of explosion is avoided (Hemming's jet). § 76. THE COMPOSITION OF WATER may be ascertained in various ways. I. By Synthesis.-If a mixture of two volumes of hydrogen and one of oxygen is detonated in an eudiometer, as just now mentioned, the gases will disappear entirely, water being formed. Again, if a current of dry and pure hydrogen be passed over a known amount of pure and thoroughly-dried black oxide of copper in a bulb-tube, to which a gentle heat is applied, the oxide will be reduced to the metallic state, water being formed, which may be collected by attaching a chloride of calcium tube, previously weighed, to the extremity of the bulb-tube, the latter being kept hot, in order to prevent the condensation of the water until it arrives at the chloride of calcium tube. After the copper is perfectly reduced, it may be weighed; the loss will represent the oxygen which has combined with the hydrogen; the increase of weight of the chloride of calcium tube will give the amount of water produced in the experiment. II. By Analysis.-The decomposition of water by the galvanic current may be also resorted to for demonstrating its composition. If the current is allowed to pass through acidulated water contained in a glass vessel, the poles of the battery being terminated by platinum-plates, which are introduced into the bottom of the latter in such a manner that they pass up a little way into separate graduated tubes, in which the gas is collected as it is generated at each pole, it will be found that the tube over the negative pole is filled with gas, while that over the positive pole is only half-filled (the dimen sions of the tubes being alike); upon examination of the gas, that evolved at the positive pole will be found to be pure oxygen, while that collected at the negative pole is hydrogen (§ 17). This experiment proves, therefore, that water consists of 1 volume of oxygen to 2 of hydrogen; and by calculation from the known specific gravities of these gases, this proportion will be found equal to 1 by weight of hydrogen, and 8 of oxygen. $77. Properties of Water.-At ordinary temperatures (of warm and temperate climates), water is, when pure, a colorless, tasteless, and inodorous liquid. It solidifies to ice or snow at 32° F. (0° C.) It may, however, when perfectly tranquil, be cooled down to a temperature far below the freezing point, without solidifying, but if then agitated in the slightest degree, it will instantly become a solid mass, the temperature simultaneously rising to 32° F. Ice belongs in form to the hexagonal system of crystals. Snow also appears in regular hexagonal tables, and in groups of these, more or less elongated, and united in the form of a star. The specific gravity of ice is 0.9184. It is a remarkable circumstance that water, unlike other liquids, contracts when cooled beyond a certain point, and attains its maximum density at 39.2° F. (4° C.) If, therefore, a mass of water is exposed to air having the temperature of its freezing point, the upper layer will sink as it cools, until the above point of maximum density is attained, after which contraction will no longer take place, and consequently the surface will be covered with a coating of ice, which protects the rest of the liquid from further refrigeration; and herein we may perceive an admirable provision of nature for the preservation of the inhabitants of the waters during severe winters, besides the many other most important results arising from the expansion of the freezing water, such, for instance, as the disintegration of rocks, &c. When impure water freezes, the ice which separates is generally free from impurities; thus, when sea-water is exposed to a very low temperature, crystals of nearly pure ice are deposited, the salts remaining in the mother-liquor. Gases dissolved in water also separate when the latter is frozen, and remain imprisoned in the ice in the form of minute bubbles. Ice is transparent and colorless, and a bad conductor of heat. At temperatures above 32° F. (0° C.) it melts into water; the latter boils at 212° F. (100° C.) being converted into an invisible vapor (steam). The specific gravity of aqueous vapor is 0.622, 100 cubic inches weighing, at 212° F. (100° C.) 14.96 grains.3 In the state of vapor, water occupies 1700 times the space which it does at ordinary temperatures in its liquid state. Water is but slightly compressible. It vaporizes at all temperatures, even when in the state of ice, in the coldest climes; hence aqueous vapor is continually ascending into the air from the surface of the earth, to which it returns when condensed, in the form of dew, rain, hail, snow, or rime (hoar-frost). Water is a perfectly neutral body; yet it combines with a great number of substances, forming what are termed hydrates. With chlorine and bromine, and with these elements only, it forms hydrates, containing 10 atoms of water. It also combines with acids and with bases, forming hydrates which correspond generally in their composition to the neutral salts of these substances; it there'fore occupies, at times, the place of a base, and at others that of an acid. With neutral salts, water enters into combination in two different conditions; first, as water of crystallization, which is easily expelled by heat; secondly, as saline or constitutional water, which is more difficult to separate from the salt (§ 21). Water possesses the property of dissolving the greater number of substances, acting almost invariably as a simple solvent. By this means solids are converted into the liquid state; this property of water is of the highest importance to chemists, enabling them to effect with ease chemical changes which would otherwise be accomplished with difficulty. The solvent power of water is much increased by an elevation of temperature, as we have already noticed, and this is also the case with steam; the solvent action of water at high temperatures is economically applied, in the apparatus known as Papin's digester, to the extraction of nutritious portions of animal food. § 78. Water cannot occur pure in nature, on account of its solvent property. Rain, which is the purest kind of water, always contains carbonate and nitrate of ammonia. Spring-waters are contaminated to a greater or less extent with various salts, which are extracted from the earth, such as carbonate of lime (chalk), sulphate of lime (gypsum), chloride of sodium, and other alkaline salts. Much carbonate of lime is frequently held in solution in water by free carbonic acid, which forms with it a bicarbonate. When such waters are boiled, the carbonic acid is expelled, and the carbonate of lime precipitated in the crystalline form, together with a certain amount of sulphate of lime and sesquioxide of iron, forming a very hard incrustation on the bottoms of steam-boilers, the safety of which is often thus endangered. 1 Grove has found that water is resolved into its elements at very high temperatures. The extremity of a platinum wire was fused into a small button, afterwards raised to a temperature approaching its fusing point by the oxyhydrogen blowpipe, and then suddenly plunged into water; a mixture of oxygen and hydrogen was immediately evolved. Aqueous vapor was also decomposed by passing it through a platinum tube heated to whiteness, and by the influence of electric sparks passing from pole to pole. 2 The white clouds of steam formed when aqueous vapor of considerable tension escapes into the atmosphere, should be distinguished as vesicular vapor, since it consists of a number of vesicles formed by minute drops of water, and distended by true aqueous vapor. 3 It must be remembered that the standard with which the specific gravities of vapors are compared is that of dry atmospheric air at 60° F. (¿ 1.) |