however, is not known with certainty, but it has been found to contain hydrogen as well as sulphur and cyanogen: it is soluble in a solution of potash. When this substance is exposed to a strong heat in a retort, it gives off carbonic disulphide and sulphur, and an orange-yellow residue is left, consisting of carbon and nitrogen only this residue bears a dull red heat without decomposition, and constitutes in a crude form the substance to which Liebig gave the arbitrary name of mellon, E,N1; but if the temperature be raised still further it is converted into a mixture of 3 volumes of cyanogen and I volume of nitrogen.

If a saturated solution of potassic sulphocyanide be mixed with 8 or 10 times its weight of concentrated hydrochloric acid, it is decomposed, hydrocyanic acid is evolved, and the solution becomes semi-solid from the separation of hydropersulphocyanic acid (H,Cy2S) in crystalline needles. These crystals are sparingly soluble even in boiling water, and as the solution cools it deposits the acid in beautiful orange-coloured needles.

13

9

No13)

(1593) Mellon (Є,N13; Liebig).—This anomalous compound was originally supposed by Liebig to contain E,N,, but he has since repeated and varied his experiments upon it, and has altered its formula as above. Mellon is not known in an isolated form in a state of purity, but it constitutes the principal portion of the solid residue obtained by heating the yellow precipitate occasioned by chlorine in solutions of the sulphocyanides. Mellon appears to be a tribasic radicle, which forms with hydrogen an acid termed hydromellonic acid (H,E,N13); this latter is an unstable compound which yields three salts with potassium; a normal mellonide, K ̧‚¤‚N13, 5 H2O; a soluble acid mellonide, K,H‚¤‚N, 3 Ꮋ Ꮎ ; and an insoluble acid mellonide, KH,,,N13. The normal mellonide is usually formed as a secondary product during the preparation of potassic sulphocyanide; but it is more plentifully obtained by fusing three parts of pure potassic sulphocyanide, and gradually adding about one part of crude mellon; it is very soluble in hot water, from which it crystallizes on cooling with 5 H2O. Its solution has an intensely bitter taste. A solution of potassic mellonide produces white insoluble mellonides when mixed with solutions of nitrate of silver, of corrosive sublimate, and of acetate of lead.

9

2

13'

When potassic mellonide is boiled with an excess of caustic potash, it is decomposed, and a new tribasic acid, the cyameluric (H ̧¤ ̧Ñ‚Ð ̧) is formed: various other compounds are also obtained by its decomposition, for details regarding which the reader is referred to Liebig's paper (Liebig's Annal. xcv. 257).

768

MELAM AND ITS DERIVATIVES.

(1594) Melam.-When ammonium sulphocyanide is submitted to distillation it undergoes decomposition, and yields a mixture of carbonic disulphide, sulphuretted hydrogen, and ammonia, whilst there remains in the retort a grey insoluble residue, which Liebig has called melam (EH,N1, Liebig; or Є,H,N, Gerhardt, calculating from Voelckel's analysis) :

Ammon. sulphocyan.

Melam.

8 (H,N,ENS) = 2 ES2 + 4 H2S + 5 H ̧N + ¤¿H‚Nμ•

The same substance may be procured by heating an intimate mixture of equal parts of potassic sulphocyanide and sal-ammoniac. In this process potassic chloride and ammonium sulphocyanide are formed, and the sulphocyanide is decomposed by the high temperature, as before, leaving melam, from which the chloride of potassium may be removed by washing.

Melam is a greyish-white granular powder, insoluble in cold water, and in alcohol and ether. Boiling water dissolves it sparingly, and deposits it in the form of a white voluminous powder. When boiled with a solution of potash it is dissolved, and a series of compounds are formed, all of which are closely related. The first of these bodies has been called melamine (HN). It is possessed of basic powers, and is deposited in brilliant, colourless, rhombic octohedra; it forms crystallizable salts. A solution of melamine precipitates the oxides of zinc, iron, manganese, and copper from their salts; with nitrate of silver it gives a white crystalline precipitate (Ag¤ ̧H ̧Ñ‚ÑÐ ̧). Melamine is polymeric with cyanamide (1600), and isomeric with cyanuramide, (H,N),Є,N,, if not identical with it. If the motherliquid from which the melamine has been deposited be neutralized with acetic acid, a voluminous white precipitate of ammeline (E,H,N,O) is produced: this substance is a feeble base, which forms a crystallizable salt with nitric acid.

3

3 3

6 9 9

6 6

When either melamine or ammeline is dissolved in strong sulphuric acid, or when melam is treated with hot nitric acid, and the solution is diluted with twice its bulk of water, and then with alcohol, a white powder termed ammelid (E.H,N,O3) is precipitated. It is insoluble in water, but is easily soluble, by the aid of heat, in solutions of potash and of ammonia. When either melam, melamine, ammeline, or ammelid is dissolved in concentrated sulphuric acid, and maintained at a temperature just short of boiling for two or three days, until on dilution it ceases to give a precipitate when neutralized with ammonia, it undergoes a change, in consequence of which the elements of ammonia are removed,

MELAM AND ITS DERIVATIVES.

3 3

769

and those of water are assimilated: and on evaporating the liquid, cyanuric acid (H ̧¤ ̧Ñ‚Ð ̧) is obtained in crystals. In fact, melamine, ammeline, and ammelid may be viewed as amidated derivatives of cyanuric acid, although they have not as yet been obtained directly by acting upon the compounds of cyanuric acid with ammonia. Two other bodies of acid character, viz., the melanuric* and cyameluric acids, also belong to the same group, as may be seen by the following equations, which illustrate the relations of composition which they all bear to cyanuric acid, and the successive stages by which they are produced:

The formation of melamine and of ammeline from melam is readily explained, since

Kekulé has represented the relations of some of these bodies by the following formula:

Cyanuric acid contains a triple cyanic acid [EN(OH)], and in the other three compounds compared with it, each group in succession is displaced by an atom of cyanamide, in which the hydroxyl (OH) of the cyanic acid is displaced by amidogen NH.

3

(1595) Cyanuric Acid (H ̧¤ ̧Ñ‚Ð ̧, 2 H2, or 3 HO,C ̧Ñ ̧O 4 HO). This polymeride of cyanic acid may be obtained in various ways. 1. By the action of sulphuric acid upon melam or its deriva

*Melanuric acid is obtained by heating urea beyond its point of fusion; 4ЄH,N20€,H,N,2+ 4 H2N + €0.

=

770

2

CYANURIC ACID.

3 3'

3

3

tives, as just described. 2. By the action of a current of dry chlorine upon fused urea; sal-ammoniac, nitrogen, and hydrochloric acid, are thus produced, and cyanuric acid is formed in abundance, 6 ЄH ̧N2+ 3 Cl2=N2+2 HCl +4 H ̧NC1 +2 H ̧¤ ̧ ̧ ̧: the salammoniac may be removed by washing with cold water, and the cyanuric acid may be crystallized from boiling water. 3. By decomposing urea hydrochlorate by heat: if the compound formed by transmitting dry hydrochloric acid gas over powdered urea be heated to 293° (145° C.) in an oil bath, rapid decomposition occurs, sal-ammoniac is sublimed, and pure cyanuric acid may be obtained by crystallizing the residue from boiling water; 3 (ЄH ̧N,,HCI)=3 H ̧NCI+H ̧¤ ̧Ñ ̧Ð ̧· 4. By heating urea beyond its fusing point until it has become converted into a dry greyish mass, resembling ammelid in appearance and properties: when this residue, which consists of melanuric acid (E,H,N,O), is dissolved in hot oil of vitriol, to which a small quantity of nitric acid has been added for the purpose of removing the colour, it combines with the elements of water, and at the same time ammonia and cyanuric acid are formed; for ЄH ̧Ñ ̧Ð ̧+H ̧Ð= H2N+H ̧¤ ̧Ð ̧Ð ̧: the cyanuric acid is deposited on diluting the liquid moderately with water. 5. By the destructive distillation of uric acid; cyanuric acid being one of the products obtained in this operation. 6. By decomposing solid chloride of cyanogen by prolonged boiling with water, or by dissolving the solid chloride in hydrated alcohol: in the latter case the liquid becomes hot, emits hydrochloric acid, and slowly deposits cyanuric acid in cubes :— ¤ ̧N ̧Cl2+3 H2=3 HCl + H ̧¤ ̧Ñ ̧Ð ̧.

3 3 3 3

3

3

4

Cyanuric acid is deposited from its aqueous solution in colourless rhombic prisms, which are efflorescent. It is sparingly soluble in cold water, more freely so in boiling water, and is also somewhat soluble in boiling alcohol. When crystallized from hot hydrochloric or nitric acid, it is deposited in square-based anhydrous octohedra. By long boiling with the concentrated acids it is decomposed into carbonic anhydride and ammonia. When crystallized cyanuric acid is distilled, it is converted into normal cyanic acid, and this hydrate in a few minutes begins to undergo a spontaneous change into the white insoluble compound known as cyamelid (504), while the temperature rises spontaneously, owing to the solidification of the mass.

Cyanuric acid is generally considered to be tribasic ;* its salts

* Wöhler, however, regards cyanuric acid as dibasic, and considers that part of the hydrogen above reckoned as basic enters into the composition of the acid. (Liebig's Annal. lxii. 241.)

ISOMERIDES OF CYANURIC ACID-FULMINIC ACID.

2 31 3 31

771

Most

with lead and with silver contain 3 equivalents of metal. of the cyanurates are sparingly soluble in water. Those formed from the alkalies and from the alkaline earths contain only two equivalents of metal. An acid ammonium cyanurate (HN H ̧¤ ̧Ñ ̧Ð ̧‚Í‚Ð) may be obtained in brilliant efflorescent prisms; and an acid potassic cyanurate (KH,¤ ̧N,,) is deposited in anhydrous cubes, when acetic acid is added in small quantities at a time to a solution of potassic cyanate; three molecules of cyanic acid coalescing to form one molecule of the polymeric cyanuric acid :

3

Potassic acetate. Potassiodihydric cyanurate.

2

3 3

3 K€NᎾ + 2 H€ Ꮋ Ꮎ, = 2 KЄ2H ̧Ð2+ KH ̧¤ ̧Ñ„Ð ̧. When a solution of a salt of copper, after being saturated with ammonia, is mixed with a solution of cyanuric acid, a characteristic violet precipitate, which is insoluble in cold water, is formed. Cyanurate of silver (AgNO3) is white, and insoluble in water. but soluble in dilute nitric acid. A remarkable acid cyanurate of silver (hydro-diargentic cyanurate), Ag2H¤ ̧Ñ ̧Ð ̧, may also be obtained.

(1596) Isomerides of Cyanuric Acid.-Sometimes during the preparation of cyanuric acid, by boiling crude mellon (1592) with nitric acid, crystals of an acid isomeric with the cyanuric are formed. It crystallizes in long oblique rhomboidal prisms, which are efflorescent: it resembles cyanuric acid, but is distinguished from the latter by its greater solubility; Liebig terms it cyanilic acid.

(1597) Fulminic Acid.-This remarkable body has not hitherto been isolated. When a solution of nitrate of silver or of mercury in an excess of nitric acid is heated with alcohol, a decomposition attended with a copious evolution of gas occurs, and a crystalline deposit of a metallic fulminate is formed.

Fulminic acid is generally assumed to be dibasic, but its power of saturating bases differs from that of dibasic acids in general. Fulminates may be obtained with 2 equivalents of a monad metal; or with 1 equivalent of metal, and 1 equivalent of hydrogen, in which latter case the compound has an acid reaction. The 2 equivalents of basyl may consist of 2 equivalents of the same metal, or they may consist of two different metals; for example, fulminates containing 2 equivalents of silver, 2 of mercury, or 2 of copper may be obtained, or double fulminates of copper and mercury, or of mercury and silver, may be procured; double fulminates of any of these metals with the metals of the alkalics,