Ammonia. This impurity in the atmosphere is generated by the putrefaction of nitrogenized organic substances; though it may be distinctly detected in air, and particularly in rain water (by which it is absorbed from the atmosphere), its quantity is very inconsiderable. It is absorbed in a remarkable manner by some substances when exposed to the air. Thus, sesquioxide of iron, or white clay, previously ignited, will be found when heated after protracted exposure to the air, to evolve considerable quantities of ammonia.

Besides the above impurities, a few others are at times to be detected in the air or in rain-water, particularly in the neighborhood of large towns; the chief of these is hydrosulphuric acid. Certain organic matters are also contained in the air. It is supposed that the contagious matter of several epidemic diseases exists in the form of an organic poison disseminated through the atmosphere, and to which the name of miasma has been given. Marsh-gas is also an impurity found in the air in the neighborhood of stagnant waters, or in coal-mines, where it forms the highly dangerous fire-damp.

The average composition of the air is always the same, since a most simple and beautiful balance is kept up in nature between animal and vegetable respiration. As already stated, the oxygen consumed in the production of carbonic acid by combustion in air or respiration of animals, is continually restored to the atmosphere by the plants, which retain for their own nourishment the carbon, to serve again as support for animal life.

The constitution of atmospheric air was for a long time matter of dispute; it is now, however, generally believed to be a mechanical mixture of oxygen and nitrogen, the constant composition of which may be accounted for by reference to the law of diffusion, and by a consideration of the slight difference in the specific gravities of its component gases.

The following arguments may be cited in support of this view:

:

1. The composition by volume of atmospheric air would be anomalous, if it were a combination of nitrogen and oxygen.

2. The properties of air are such as would be predicted of a mere mechanical mixture of the two gases.

3. A mixture of nitrogen and oxygen in proper proportions exhibits all the properties of atmospheric air, without our perceiving any of the phenomena usually attendant upon chemical combination.

4. Water, exposed to air, absorbs each gas in the same proportion as if it were in a perfectly free state.

§ 89. We are not acquainted with this body in a separate state; we have, however, very good reasons for assuming its existence in many compounds.

When potassium and sodium are heated in ammoniacal gas, it will be found that one-third of the hydrogen escapes; the residue has the composition KNH,, or NaNH,:–

NH+K=KNH,+H.

This compound is termed amidide, or amide of potassium.

When certain metallic chlorides are mixed with aqueous ammonia, compound amides are also produced :

2HgCl+2NH,

HgNH,.HgCl+NH,CI.

A far larger number of amides exist in organic chemistry, consisting of amidogen in combination with some other complex atoms. When brought into contact with water in the presence of acids or alkalies, they are resolved into ammonia and oxidized products.

AMMONIA.

NH. Eq. 17. Sp. Gr. 0.5902.

Composition by Volume.-1 volume of nitrogen and 3 volumes of hydrogen combine to form 2 volumes of ammonia.

§ 90. Ammonia occurs in the air as carbonate of ammonia; in some rivers, springs, and mineral waters, as chloride of ammonium, or some other salt. The rock-salt of the Tyrol contains chloride of ammonium (sal-ammoniac); sesquioxide of iron and aluminous or ferruginous rocks, after exposure to air, yield ammonia when heated; some plants contain salts of ammonia; it is also found in one or two minerals of recent formation, and in animal secretions.

When a mixture of 2 volumes of nitric oxide and 5 volumes of hydrogen is passed over spongy platinum, or other porous substances (heated to redness), ammonia and water are produced. The quantity formed by exposing a mixture of nitrogen and hydrogen gases to the action of an electric current is very minute; but if hydrogen, at the moment of its liberation, meet under certain circumstances with nitrogen, ammonia will be produced. In the rusting (oxidation) of iron by water containing atmospheric air, ammonia is formed in this manner. Most nitrogenized organic substances yield ammonia, either by dry distillation, or by heating with an alkali. Animal secretions yield ammonia in abundance, when allowed to undergo fermentation or putrefaction. Thus, in urine, the urea (cyanate of ammonia) gradually passes over into carbonate of ammonia :

Large quantities of ammonia are also obtained in the distillation of coal (for the preparation of gas) and of bones; and from these sources most of the ammonia of commerce is at present obtained.

Carbonate of ammonia was first extensively prepared from camels' dung, in Egypt.

Preparation.-The best mode of preparing dry ammonia in the laboratory, is to heat gradually in a retort or flask, a mixture of 1 part of chloride of ammonium, and 2 parts of hydrate of lime, allowing the gas to pass first into a small bottle with a safety-tube, in which any moisture may be to a great extent condensed, and afterwards through a tube filled with fragments of quicklime, to complete the desiccation of the gas, which must either be collected over mercury, or by upward displacement in inverted vessels, it being considerably lighter than air. The production of ammonia in this process is thus represented:

NH,C1+CaO.HO=CaCl+NH,+2HO.

Properties.-Ammonia is a colorless gas, of a peculiar and exceedingly pungent odor; it does not support combustion, but a jet of the gas burns with a yellow flame in an atmosphere of oxygen. When inspired pure, it is fatal to animals. It is converted by a pressure of six and a half atmospheres at 50° F. (10° C.) into a colorless, mobile liquid, the spec. grav. of which is 0.76; gaseous ammonia is likewise transformed at a very low temperature, into a colorless, translucent, crystalline solid, which melts at -113° F. (-75° C.) Liquid ammonia may be obtained by heating some chloride of silver saturated with gaseous ammonia, in one arm of a sealed tube of tough glass (such as recommended by Faraday for the liquefaction of gases), and surrounding the other arm with ice; the ammonia will be evolved, and condensed by its own pressure

in the cold extremity of the tube. On allowing the chloride to cool, the ammonia is again absorbed by it; the heat evolved by this recombination raises the temperature of the chloride of silver to 100°.4 F. (38° C.); while the other end of the tube in which the ammonia was condensed, becomes very cold.

Ammonia is powerfully alkaline; when brought into contact with hydrogenacids, or with hydrated oxygen-acids, it produces ammoniacal salts; and hence volatile acids, such as hydrochloric, nitric, and acetic, are often used as a test for gaseous ammonia, with which the vapors of these acids produce white clouds. If a flask filled with ammoniacal gas be opened under water, the latter rushes in with great rapidity, in consequence of the absorption which takes place.

SOLUTION OF AMMONIA, LIQUOR AMMONIÆ.

Water absorbs nearly half its weight (or about 670 times its volume) of ammoniacal gas. A solution of this description constitutes the aqua ammoniæ fortissima of commerce.

It is prepared by connecting a glass or earthenware vessel, charged with the above mentioned mixture for the preparation of ammonia (slightly moistened with water), with three Woulfe's bottles, fitted with safety-tubes; the first containing but little water, the second, an amount about equal to the weight of chloride of ammonium employed, and the third, a smaller quantity.

The gas is washed in the first bottle (the first portion being also absorbed), the water in the second bottle then becomes gradually saturated with pure ammoniacal gas; that in the third retains any ammonia that may escape absorption in the second bottle. These bottles should be kept cool by being surrounded with cold water.

Properties. The solution of ammonia is colourless. It varies in spec. grav. from nearly 1.000 to 0.850, according to its strength. (The strongest ammonia of commerce has a spec. grav. of about 0.87). It does not freeze until between —36° and —42° F. (—38° —41° C.) It possesses the peculiar odor of the gas, and a sharp burning taste. The greater portion of ammonia is expelled from its solution below 212° F. (100° C.)

Solution of ammonia is most extensively used by chemists, being a highly important reagent. It is also employed medicinally, for which purpose it is diluted to the spec. grav. 0.96.

Dry ammoniacal gas, when submitted to the electric spark, is resolved into 3 volumes of hydrogen and 1 of nitrogen; ammonia may be also decomposed by contact with highly heated platinum, copper or iron, and by detonation with oxygen. Chlorine gas decomposes it rapidly at ordinary temperatures, yielding nitrogen gas and hydrochloric acid; the latter, combining with another portion of ammonia, forms chloride of ammonium; an excess of chlorine produces chloride of nitrogen (§ 97).

4NH,+C)=3(NH ̧CI)+N.

This action is at times accompanied by the production of a flash of light. Ammoniacal gas is also decomposed under various circumstances, and with more or less rapidity, by some of the oxides of nitrogen (particularly hyponitric acid), by some metallic oxides, &c.

AMMONIUM, NH. Eq. 18.

$91. This compound has never yet been isolated; numerous observations,

It has been very recently shown that ammonia is resolved into its elements at a temperature far below redness, when passed through tubes containing heated quicklime. It has even been proposed to employ this method for the preparation of hydrogen free from arsenic, &c., when the presence of nitrogen is not objectionable.

however, have led chemists to believe that it exists, and is in its properties similar to a metal.

If a galvanic current is allowed to act upon a solution of an ammoniacal salt, the end of the negative pole dipping into mercury, the latter is observed to increase gradually in bulk to a considerable extent, becoming of the consistency of butter, and at the same time retaining its metallic lustre. By placing an amalgam of potassium or sodium on a piece of moistened chloride of ammonium, or in a solution of the latter, the same compound is produced. This is regarded as the amalgam of mercury with the substance ammonium, NII. When it is placed in water, the mercury returns to its original state, hydrogen and ammonia being evolved. The increase in weight which the mercury exhibits when converted into the amalgam, is very trifling. The decomposition of potassiumamalgam by chloride of ammonium is represented as follows:

HgK+NH,Cl=KCl+HgNH ̧.

The assumption of the existence of the compound metal, ammonium, based upon this and other experiments, furnishes us with a very simple view respecting the constitution of the ammoniacal salts.

Ammonia was formerly believed to combine directly with hydrogen-acids and also with oxygen-acids. The composition of the hydracid salts is in accordance with this view, since they may be represented by the general formula, NH, HR;1 it is most probable, however, that if an oxygen-acid unites (as it sometimes does) directly with NH,, it does not form a true salt, but that the presence of an equivalent of water is indispensably necessary to the production of a salt of ammonia with an oxygen-acid. This difference in the behavior of ammonia with the two classes of acids is not easily explained, unless we adopt the view of Berzelius in assuming the existence of the substance ammonium, NH.

Ammonia+1 eq. of water, NH,+HO, must then be viewed as NH,O=AmO, the oxide of ammonium, analogous to KO, the oxide of potassium or potassa; this oxide then unites with oxygen-acids to form salts of the oxide of ammonium, such as NH,O.SO, or AmO.SO; NH, HCl, the hydrochlorate of ammonia, must in this case be viewed as NH Cl, or AmCl, chloride of ammonium, analogous to chloride of potassium. An analogy between the salts of ammonia, and those of the alkalies to which they are, in many respects, so similar, cannot be traced by the first mode of viewing their composition; but as soon as we assume the existence of ammonium, the most striking analogy is, as we have shown, exhibited between the composition of the salts of ammonia and of potassa or soda; the main difference consisting in the point, that Am(NH) is a compound, while K and Na are elements; several analogous cases are, however, to be found in chemistry, in which a compound body, the chemical or physical properties of which are indeed perfectly well known, comports itself towards other bodies exactly like certain elements; and, indeed, most chemists are far from maintaining the impossibility of a future discovery that some of the present elements are compound bodies (§ 101).

Various objections have been raised to the ammonium-theory of Berzelius, and other theories have also been advanced; the above is, however, the most simple, and hence is most generally adopted by chemists.

1 R representing the radical of the hydrogen-acid.

CHLORINE.1

Sym. Cl. Eq. 35.50. Sp. Gr. 2.44.

§ 93. Scheele discovered chlorine in 1774. Gay-Lussac and Thénard were, however, the first to class it among the simple bodies in 1809. Its elementary character was afterwards fully established by Davy.

Chlorine occurs in combination in many mineral substances, such as rock-salt (chloride of sodium), also in sea-water and marine plants, as chlorides of sodium and potassium.

Preparation.-Chlorine is obtained :—

I. By gently heating in a flask, binoxide of manganese with strong hydrochloric acid :

MnO,+2HCl=MnCl+2HO+Cl.

II. By heating a mixture of binoxide of manganese, chloride of sodium, and moderately dilute sulphuric acid:

MnO,+NaCl+2(HO.SO2)=MnO.SO,+NaO.SO,+2HO+Cl.

When chlorine is required perfectly dry, it should be passed through concentrated sulphuric acid.

The gas may be collected either by downward displacement (§ 31), or if required perfectly free from atmospheric air, over water, the delivery-tube being passed to the top of the gas-jars.1

Properties.-Chlorine is a yellowish-green gas, of a pungent suffocating odour; it is incombustible, and supports the combustion of a few bodies for which it has an affinity. Some elements, such as antimony and phosphorus, inflame spontaneously in chlorine, as also certain compounds rich in hydrogen, such as ammonia and oil of turpentine; a wax taper continues to burn for some time in this gas, with deposition of carbon, the hydrogen of the wax combining with the chlorine, which has a most powerful affinity for that element. Chlorine is incapable of supporting respiration, causing instantaneous death when inhaled pure; when breathed in small quantities, it excites cough and sneezing, accompanied by an oppressive and choking sensation in the chest, sometimes followed by spitting of blood. When highly diluted, it may, however, be administered, to alleviate symptoms of phthisis.

It may be condensed by a pressure of about four atmospheres to a yellow limpid liquid, of spec. grav. 1.33.

Chlorine, especially when moist, discharges vegetable colors. It also possesses the remarkable property of destroying organic odors and infectious matters.

Two views are taken of this property of chlorine. In cases when dry chlorine is employed, it appears to abstract hydrogen directly from the substance, thereby converting the latter into some colorless or inodorous body; but if water is present (and moist chlorine bleaches much more rapidly than the dry gas), its hydrogen is most probably abstracted by the chlorine, and the liberated oxygen acts upon the organic matter, either destroying it entirely, or converting it into some colorless or inodorous product.

Water dissolves about twice its volume of chlorine gas at ordinary temperatures. (The solution may be prepared by passing a slow current of chlorine

1 Xago, yellowish-green.

2 Maumené has recommended another process for the preparation of chlorine, when the admixture of nitrogen would not be objectionable. 75 parts of dry nitrate of ammonia, 25 of dry chloride of ammonium, and 400 of sand, are mixed, and heated in a capacious flask or retort.