With phosphoric chloride it gives, on warming, solid cyanogen chloride :

C3N303H3 + 3PC1, 3POC1, + 3HCl + C3N3C13.

=

This last reaction agrees better with the structural formula:

HO.CON

N-C.OH

HO.C N

than with that for a tri-isocyanic acid :

0-C-N-H

H-N C-0

O-C-N-H

SULPHOCYANOGEN COMPOUNDS.

105. The alkaline salts of sulphocyanic acid are obtained from the alkaline cyanides by direct addition of sulphur, and the combination takes place not only by melting the ingredients, but even by boiling them together with water.

Sulphocyanic acid is obtained by addition of strong mineral acids to its salts; if an excess of the acid has been employed, it readily splits up into hydrocyanic acid and persulphodicyanic acid.

It is usually prepared by decomposition of its mercury salt by dry hydrochloric acid or hydric sulphide :

Hg

S-CEN
S-CEN

+ H2S HgS + 2H-S-CEN,

=

as a colourless liquid of pungent acetous odour, which solidifies at -12.5° to hexagonal plates. At higher temperatures (towards 100°) it boils, the greater part suffering the decomposition above mentioned. When damp, it decomposes into ammonic carbonate, carbonic disulphide, and hydric sulphide :

or

2(CN)SH + 3H20 = (NH4)2CO3 + CS2

(CN)SH + 3H20 = (NH1)HCO3 + SH2,

and yields carbonic oxysulphide by warming with very dilute sulphuric acid:

Its aqueous solution has a strongly acid reaction, and can only be kept, for any length of time, at low temperatures. It colours ferric salts blood-red, from formation of ferric sulpho-cyanate, and, on account of the intensity of this colour, is used, in the form of any of its soluble salts, to detect small traces of iron.

106. Potassic sulphocyanate is generally prepared by heating a

mixture of forty-six parts of dry potassic ferrocyanide, seventeen parts potassic carbonate, and thirty-two parts of sulphur. The ignited mass is boiled with alcohol, and on cooling, the salt separates in long, clear, striated plates, which deliquesce in moist air, and melt on gently heating.

The ready formation of this salt is used as a means of detecting small quantities of sulphur. For this purpose, the substance to be tested for sulphur, or a sulphide, is heated with some dry potassic cyanide, the mass, when cold, extracted with water, the liquid rendered slightly acid and tested with ferric chloride; a blood-red colour shows the presence of sulphur.

Sodic sulphocyanate is prepared similarly to the potassium salt; it occurs in small quantity in saliva, and can be detected therein by ferric chloride.

107. Ammonic sulphocyanate is prepared on the large scale by boiling ammonic cyanide solution (wash-water from gas-works) with sulphur, also by heating carbonic disulphide with alcoholic ammonia : CS2+4NH, NH1.SCN + (NH4)2S.

=

It is also easily formed by mixing prussic acid with yellow ammonic sulphide, and evaporating off the excess of the latter on the water bath:

2HCN + (NH4)2S3 = 2 (NH ̧) SCN + H2S.

This last reaction affords an excellent means of testing for small quantities of prussic acid.

Ammonic sulphocyanate forms readily soluble crystals, quite similar to those of the potassic salt, which melt without change at 147°, and at 170° begin to suffer an analogous decomposition to that which occurs to ammonic cyanate at ordinary temperatures; namely, it forms sulphurea:

108. The sulphocyanates of the alkaline earths, and of the metals of the zinc and iron group, are soluble in water, partly also in alcohol. Ferric sulphocyanate is an uncrystallisable, nearly black, deliquescent mass, which dissolves in water and alcohol with deep blood-red colour. The sulphocyanates of copper, lead, silver, and mercury are obtained by double decomposition as insoluble precipitates. By mixing solutions of the mercury nitrates and potassic sulphocyanate, the respective mercury salts are obtained :

Hg(SCN), mercurous sulphocyanate as amorphous and Hg(SCN), mercuric sulphocyanate as crystalline

black precipitates. Both burn on heating, with remarkable swelling and evolution of mercury vapour, and leave behind an extraordinary (Pharaoh's serpents) of crude mellone (§ 122). 109. The anhydride of sulphocyanic acid: cyanogen sulphide,

voluminous mass

EN

(CN),SSC, is obtained in clear rhombic tables, by acting on argentic sulphocyanate with an ethereal solution of cyanogen iodide : Ag-S-CEN+I-CEN=AgI + S (CN)2,

and evaporating the liquid. It smells like the iodide, sublimes even at 30° in thin leaves, and fuses at 65°. It is soluble, unchanged in alcohol, ether, and carbonic disulphide. The aqueous solution decomposes readily with separation of a yellow powder. With potassic hydrate solution, cyanogen sulphide yields potassic cyanate and sulphocyanate :

(CN),S + 2KOH=KOON + KSCN + H,O.

110. Isosulphocyanic acid is still unknown, but the potassic salt, S—C—N—K, is obtained by warming persulphocyanic acid (following paragraph) with alcoholic potassic hydrate, in the form of granular crystals, whose aqueous solution is not reddened by ferric salts, and yields coloured precipitates with cobalt, nickel, and cadmium salts. If the solution of the potassic salt is boiled for a long time, or if the dry salt be heated to melting, it is converted into the ordinary sulphocyanate. The true sulphocyanates are more stable at high temperatures than the isosulphocyanates, whilst with the oxycyanates exactly the reverse is the case, probably in consequence of the greater affinity of oxygen for carbon.

2

111. Persulphodicyanic acid (persulphocyanic acid), C2N,H,S3, separates slowly in yellow needles, with evolution of hydrocyanic acid, when a saturated solution of potassic sulphocyanate is mixed with six times its bulk of concentrated hydrochloric acid :

3KSCN +3HCI 3KCl + HCN + H2N2C2S3.

=

The precipitate is purified by solution in dilute ammonia, and the ammonic salt so formed decomposed at the boiling temperature by hydrochloric acid. On cooling the compound crystallises in goldenyellow needles, difficultly soluble in boiling water. With the alkalies persulphocyanic acid forms, readily soluble, with many of the heavy metals, insoluble compounds; if, for instance, a hot solution of the acid be mixed with plumbic acetate, the lead salt is precipitated in the form of a deep yellow amorphous powder, of the formula PbC2N2S3.

As the potassium salt of persulphocyanic acid, when warmed with alcoholic potassic hydrate, yields potassic isosulphocyanate (see § 110), it follows most probably that persulphocyanic acid must also be expressed as an iso compound [(CS)NH],S, whose structure would

be

112. Persulphocyanogen, or pseudosulphocyanogen, C3HN3S3. By action of strong nitric acid, chlorine, or bromine on a boiling solution of potassic sulphocyanate, persulphocyanogen separates as an orangeyellow, amorphous powder, insoluble in water, alcohol, or ether. When heated in a stream of chlorine, it yields, besides mellone and sulphur chloride, tricyanogen chloride; by heating with concentrated hydrochloric acid, it gives hydric sulphide, hydric persulphide, and cyanuric acid:

C3H3N3S3 + 3H2O = H2S + H2S2 + C3N3O3H3.

According to both reactions, it is a derivative of tricyanogen of the probable formula :

S

(C3N3) S

= tricyanogen persulphide sulphhydrate.

SH

NITROGEN COMPOUNDS OF CYANOGEN.

113. By combination of the carbon of true cyanogen, in both the single and polymerised modifications, with the nitrogen of ammonia residues, there results the amide compounds of cyanogen, of which the tricyanogen compounds are especially numerous.

NH2

When the vapour of cya

nogen chloride is passed into anhydrous ether saturated with ammonia, ammonic chloride immediately separates, and the ether contains cyanamide dissolved, which is obtained on evaporation in colourless, readily soluble crystals, melting at 40°. If the solution be decomposed by ammonia and argentic nitrate, a yellow precipitate of argentic cyanamide, (CN)NAg2, is obtained.

From a solution acidulated with nitric acid, there separates, in a short time, leaf-like crystals of urea nitrate :

NH,

By the action of aqueous ammonia cyanamide polymerises to dicyanodiamide; by heating above its melting point, it is converted, with great evolution of heat, into melamine, and by warming with ammonic chloride, is changed into guanadine hydrochlorate (§ 127).

solution of true potassic cyanate (§ 102) with potassic hydrate, dicyanimide is formed, together with the carbonate, probably according to the equation :

It has not yet been obtained in a perfectly pure state, its existence being inferred from the result of adding argentic nitrate to the solution previously neutralised with nitric acid, when a white precipitate, not affected by light, is obtained, of the formula (CN),NAg.

Dicyanodiamide.

116. Dicyanodiamide, or param, C2N ̧H1 = (C2N2) (NH2)2, results from the spontaneous polymerisation of cyanamide in aqueous ammoniacal solution. It is also formed by desulphurising sulphurea by mercuric or argentic oxides :

It crystallises in colourless leaves, which melt unchanged at 205°, dissolve pretty easily in water and alcohol, but little in ether. With argentic nitrate, dicyanodiamide yields a compound

which on addition of ammonia is converted into argentic dicyanodiamide

(C,N,NHẬP

If a solution of dicyanodiamide be evaporated with hydrochloric acid, there remain large tables of dicyanodiamidine hydrochlorate:

(C2N2) (NH2)2 + H2O + HCl = C2H6N,O.HCl,

from which dicyanodiamidine can be separated. This latter is readily soluble in water, difficultly in alcohol, has strongly basic properties, and yields well-crystallised salts. It results from dicyanodiamide by the addition of the elements of water, probably according to the equation:

and is therefore a body intermediate between urea and guanidine (§ 127).