When a solution of ammonia is heated the gas is rapidly evolved, and at the boiling temperature the whole of it is given up.

The great solubility of this gas in water may be shown by filling a large bolt-head flask with ammonia by displacement, the flask being closed by means of a cork through which a long tube passes, as shown in Fig. 57. On removing the cork from the end of the tube water slowly rises until it reaches the top, and as soon as the first drops enter the globe the absorption

proceeds with great rapidity, the water being forced up the tube in the form of a fountain, which continues until the flask is filled.

Commercial liquor ammoniæ is prepared by passing ammonia gas into water; the strongest solution has a specific gravity of 0.882 at 15°, and contains 35 per cent. of ammonia. During the process of solution heat is liberated, and when the gas is again expelled the same amount of heat is reabsorbed. If a rapid stream of air be driven through a quantity of strong ammonia solution, contained in a glass flask, the ammonia gas is quickly expelled; and if the flask be placed upon a wooden block, as seen in Fig. 58, upon which a few drops of water have been poured, it will be found that after a few moments the flask will have become firmly frozen to the block. By the rapid evaporation of ammonia in this way it is possible to lower the temperature to -40° C.

FIG. 57.

Ammonia is an easily liquefiable gas; thus at 15.5° it requires a pressure of 6.9 atmospheres, and at o° only 4.2 atmospheres, in order to liquefy it. The gas was first liquefied by Faraday (1823) by heating in one limb of a closed and bent glass tube (see Fig. 2) a quantity of a compound of ammonia with silver chloride, the other limb of the tube being immersed in a freezing-mixture. The experiment may be made in a tube constructed as seen in Fig. 59. The wide limb is nearly filled with dry precipitated silver chloride which has been saturated with ammonia gas. This compound melts at about 38°, and at a somewhat higher temperature it gives up its ammonia. If the narrow limb of the tube be immersed in a freezing-mixture while the compound is being heated, the combined influence of the cold and the pressure exerted by the

evolved ammonia will cause the gas to liquefy and collect in the cold portion of the tube. On removing the tube from the freezingmixture and allowing the other end to cool, the liquid ammonia will boil off and be reabsorbed by the silver chloride, reforming the original compound.

Liquid ammonia is easily obtained in larger quantity by passing the gas through a glass tube immersed in a bath of solid carbonic acid and ether. Liquid ammonia is a colourless, mobile, and highly refracting liquid, boiling at -33.7°, and having a specific gravity at o° of 0.6234. When cooled below -75° it solidifies to a mass of white crystals.

Liquid ammonia dissolves the metals sodium and potassium, the solution in each case being of an intense blue colour. On the evaporation of the liquid the metal is deposited unchanged.

During the evaporation of liquid ammonia, boiling as it does at so low a temperature as - 33.7°, a rapid absorption of heat takes place, and as this substance is so easily obtained it was one of the earliest liquids employed for the artificial production of ice. Various ice-making machines have been invented by M. Carré, in which the reduction of temperature required is obtained by the evaporation of liquid ammonia.

Ammonia is decomposed into its elements at a temperature below a red heat. In this decomposition two volumes of ammonia give one volume of nitrogen and three volumes of hydrogen. The gaseous products, therefore, obtained by passing ammonia through a red-hot tube are inflammable. In the same way, when electric sparks are passed through ammonia, the gas is resolved into its constituents. By performing this experiment upon a measured volume of ammonia confined in a eudiometer over mercury, it will be found that after the passage of the sparks for a short time and

the readjustment of the levels of mercury, the original volume of the gas has been doubled.

The fact that the hydrogen and nitrogen are present in ammonia in the proportion of three volumes of hydrogen to one of nitrogen can be shown by taking advantage of the fact that ammonia is decomposed by chlorine, the latter combining with the hydrogen to form hydrochloric acid and the nitrogen being set free. This is effected by means of the apparatus shown in Fig. 60. The long glass tube, divided into three equal divisions, is filled with chlorine and closed by a cork carrying a small dropping funnel. A few cubic centimetres of strong aqueous ammonia are poured into the funnel and allowed to enter the tube drop by drop. As the first two or three drops fall into the chlorine it will be seen that the combination is attended with a feeble flash of light, and fumes of ammonium chloride are formed. When the reaction is complete the whole of the chlorine will have combined with hydrogen derived from the ammonia to form hydrochloric acid, and this in its turn will combine with the excess of ammonia added, forming ammonium chloride. This substance dissolves in the water. A small quantity of dilute sulphuric acid is next introduced by means of the dropping funnel in order to absorb the remaining excess of ammonia. The atmospheric pressure is then once more restored by attaching to the funnel a bent tube, dipping into a beaker of water, as shown in the figure, and when the water is allowed to enter it will be found to flow into the tube until it reaches the second graduation. The gas which is left and which occupies one of the divisions of the tube is found on examination to be nitrogen. This one measure of nitrogen, therefore, has been eliminated from that amount of ammonia which has been decomposed by the chlorine with which the tube was originally filled. Now chlorine combines with its own volume of hydrogen, therefore the volume of hydrogen which was in combination with the one measure of

FIG. 60.

nitrogen is equal to the volume of chlorine contained in the tube, that is to say, it was three measures. We have, therefore, one measure of nitrogen and three measures of hydrogen, or, in other words, ammonia is a combination of nitrogen and hydrogen in the proportion of one volume of nitrogen to three volumes of hydrogen. In contact with many metals at a moderately high temperature ammonia is decomposed into its elements, and a compound of the metal with nitrogen is formed. In this way, at temperatures ranging between about 400° and 800° a number of metallic nitrides have been obtained. These compounds are produced by passing a rapid stream of ammonia gas through heated porcelain tubes containing the metal in the form of either wire, foil, or fine powder. When heated in an atmosphere of hydrogen, these nitrides are decomposed into nitrogen and the respective metal, hence they can only be produced in the presence of a large excess of ammonia gas.

Ammonia combines directly with acids forming salts, known as ammonium salts, in which the nitrogen functions as a pentad element; thus with hydrochloric and sulphuric acids it forms respectively ammonium chloride and ammonium sulphate—

NH3+ HCl (NH1)Cl.

2NH3+ H2SO4=(NH4)2SO4.

(The ammonium salts will be described with the compounds of the alkali metals.)

Hydrazine (diamidogen), NH, NH2 or N2H.-This compound was first prepared by Curtius (1887). It is obtained from a salt of an organic acid

N

known as diazo-acetic acid, II N

`CH COOH. When the ethereal salt of this

acid is acted upon by potassium hydroxide, the potassium salt of another acid is formed, namely triazo-acetic acid. This we may regard as merely a polymer of the first acid, and represent its formula (N: CH COOH↳ When this compound is digested with dilute sulphuric acid it is converted into hydrazine sulphate and oxalic acid. Thus, employing the simple formela for the acid

N: CH COOH+H2SO4+2H2O=N2H ̧H2SO1+H2C2O4.

Hydrazine may also be prepared from purely inorganic sources. When hydrogen potassium sulphite acted upon by potassium nitrite, a compound known as potassium dinitroso-sulphonate is produced, O: N°N ́OK·KSQ2

Beilby and Henderson, Jour. Chem. Soc., November 1901.

The mechanism of the reaction will be made clearer if the formula for the nitrite be written O: NOK.

Thus

20: NOK+2HKSO2=O: NN·OK ·KSO2+KËSO ̧.

By the action of nascent hydrogen (from sodium amalgam) at the temperature of ice, this compound is converted into the potassium salt of hydrazine sulphonate

O: N N OK KSO2+6H=H2N•NH •KSO2+KHO+H2O.

And this compound on distillation with potassium hydroxide yields hydrazine —

HẸN NHKSO,+HKO=H,NNH,+K,SO.

The base itself may also be obtained by heating together in a sealed tube, to a temperature of 170°, hydrazine hydrate, NH, H2O, and barium monoxide. Under these circumstances the barium oxide takes up the water from the hydrazine hydrate, according to the equation

BaO+N2H1H2O=Ba(HO)2+N2H¡.

When the tube is opened, the gaseous hydrazine, which is under considerable pressure, rushes out of the tube, forming dense fumes in contact with the atmospheric moisture, with which it combines with great readiness.

Hydrazine Hydrate, N2H,H,O.-The compound formed by the combination of hydrazine with water is obtained by distilling hydrazine sulphate, N2H4H2SO4, with an aqueous solution of potassium hydroxide (caustic potash) in a vessel of silver. It is a colourless, fuming, powerfully corrosive liquid, which boils at 118.5°. It attacks glass, cork, and indiarubber, and can only be prepared in vessels of silver or platinum which are screwed together at their junctions. With the halogen acids it forms two series of salts, in which either one or two molecules of the halogen acid are present: thus with hydrochloric acid we have

Hydrazine and its salts act as powerful reducing agents, and give the characteristic red precipitate of cuprous oxide when added to Féhling's solution. This reaction serves to immediately distinguish these compounds from ammonium salts.

Hydrazoic Acid or Azoimide, HN, or HN

N

1.- Discovered by Curtius N

(1890). The sodium salt is prepared by boiling benzoylazo-imide with sodium hydroxide, when sodium benzoate and sodium hydrazoate are formed, thus