CYANOGEN. 



CYANOGEN. 



370 



Thus a beautiful blue pigment, now known to be a compound of 

 cyanogen and iron, was accidentally discovered in Prussia, at the 

 commencement of the 18th century, by Diesbach, and called by him 

 Prussian blue. From this compound Scheele, in 1782, obtained a 

 substance that on account of its source and properties he called Prussic 

 acid (hydride of cyanogen, or hydrocyanic acid). Prussic acid was 

 ascertained to be composed of carbon, nitrogen, and hydrogen, by 

 Berthollet in 1787; and Gay Lussac finally determined its true con- 

 stitution, and isolated cyanogen itself in 1815. 



Cyanogen derives its name from two Greek words, Kvavos, blue, and 

 yt vvdu, to produce, because it was first discovered in, and is an essential 

 ingredient of, Pnissian blue. 



Cyanogen is exclusively a product of the animal and vegetable 

 kingdoms. It nowhere exists free in nature. Combined with hydro- 

 gen, it occurs to a considerable extent in the juice of the bitter 

 cassava. [CASSAVA, NAT. HIST. Div.J The same compound of cya- 

 nogen is also produced by the decomposition of certain nitrogenised 

 principles in fruits, when the latter are distilled with water. [AMYG- 

 D&Lnr.J Refuse animal matter, such as the parings of hoofs, hides, 

 horns, &e., is the ultimate source of the many cyanogen compounds 

 used at the present day in the arts and manufactures. These animal 

 matters all contain nitrogen and carbon, and at a high temperature 

 furnish cyanogen. [POTASSIUM, FERROCYANIDE OF.] 



A point of considerable interest connected with cyanogen, is that it 

 was the first discovered of those compound bodies that in their com- 

 binations and general properties so much resemble elements. Its dis- 

 covery gave to organic chemistry an impetus such as it had never before 

 received, and to which it owes no small share of its present position. 



Cyanogen cannot be formed by the direct union of its elements, but 

 is easily prepared by heating bicyanide of mercury (Hg Cy 2 ) [MERCURY, 

 Bicyanide of] in a retort, or any other vessel from which gas may be 

 conveniently collected. 



Cyanogen is a transparent, invisible gas of a peculiar penetrating 

 odour. It is excessively poisonous. Its specific gravity is 1 '8064. It 

 is tolerably soluble in water, much more so in alcohol, and must there- 

 fore be collected by displacement, or better over mercury. [GASES, 

 COLLECTION OF.] It burns with a very beautiful peach -blossom 

 coloured flame. By a pressure of several atmospheres it is condensed 

 into a colourless liquid ; and at a temperature of 30 Fahr., solidifies 

 into a crystalline mass. It supports a very high temperature without 

 alteration, unless iron be present, when at a full red heat it is decom- 

 posed into nitrogen gas and carbon. 



Metallic cyanides, formed by the union of cyanogen with metals, 

 may be easily prepared by indirect methods. See the various metals. 



Cyanogen and hydrogen form only one compound. 



Jfi/</roci/an!c acid (Cy H) ; prusstc acid. The constituents of this 

 acid cannot be made to unite directly, but the compound is readily 

 formed on adding a strong acid to a metallic cyanide, cyanide of potas- 

 sium for example, and may be rendered anhydrous by passing the 

 vapour over fragments of chloride of calcium. The reaction that takes 

 place is a simple one : 



KCy + HO, SO, KO, S0 3 + HCy 



Cyanide of Sulphuric Sulphate Hydrocyanic 

 potassium. acid. of potash. acid. 



By cooling the receiver into which the vapour is conducted, the pure 

 acid is obtained as a colourless transparent liquid. 



Anhydrous hydrocyanic acid is very volatile, boiling at 797. For 

 this reason great care is requisite in the preparation and manipulation 

 of it, as the inhalation of an exceedingly small quantity of the vapour 

 rapidly destroys life. So quickly does it evaporate at common tem- 

 peratures, that a drop exposed on a glass plate soon solidifies to a mass 

 of silky fibres on account of the cold produced by volatilisation. The 

 same effect occurs in a closed tube, on reducing its temperature by 

 means of a freezing mixture to 5 Fahr. The vapour of this acid 

 burns with a white flame. 



Ihlnted hydrocyanic acid, containing two parts of the anhydrous 

 acid to ninety-eight parts of water, is a preparation much used in 

 medicine. Directions for preparing it of this strength are given in the 

 ' London Pharmacopoeia," but manufacturers, to save time and expense, 

 prepare it in a tolerably concentrated state, determine its strength by 

 means of nitrate of silver, and then so dilute it with water that one 

 hundred grains of the liquid shall precipitate the whole of the silver 

 contained in a solution of 12'59 grains of pure nitrate of silver > it then 

 constitutes the officinal preparation. The manufacture of the acid is 

 conducted in stoneware stills or large retorts. Ferrocyanide of potas- 

 sium [POTASSIUM, Ferrocyanide of], dissolved in water, and sulphuric 

 acid are introduced into the still and heat applied ; a strong solution of 

 the acid distils over and is condensed in a well cooled refrigerating appa- 

 ratus ; the end of the stoneware worm, or condensing tube, should dip 

 just below the surface of a little water contained in a vessel surrounded 

 with ice. The decomposition that takes place is thus expressed : 



2(FeCy, 2KCy) + 6(HO, SO,) = (KCy, 2FeCy) + 3(KO, HO, 28O,) + 3HCy 



Ferroeyanide Sulphuric acid. Evcritt's salt. Bisulphate of 

 of potassium. potash. 



ARTS AND SCI. DIV. VOL. HI. 



Hydro, 

 cyanic 

 acid. 



The hydrocyanic acid prepared by this process nearly always con- 

 tains a trace of sulphuric acid, but this is rather advantageous than 

 otherwise, for when quite pure the aqueous solution of the acid is very 

 liable to decompose, but does not do so when the smallest possible 

 quantity of sulphuric or hydrochloric acid is present. 



Tests for cyanogen. In all simple combinations as, for example, in 

 solution of hydrocyanic acid, the cyanogen may be detected by the 

 following methods. Solution of nitrate of silver produces a white 

 curdy precipitate sohible in boiling nitric acid, and decomposed when 

 heated in the dry state with separation of metallic silver. The addition 

 of small quantities of solutions of caustic potash or soda, protosalt of 

 iron, and persalt of iron, causes a precipitate of oxides of iron ; by the 

 addition of hydrochloric acid the oxides of iron in excess are dis- 

 solved, whilst prussian blue of characteristic colour remains suspended 

 in the liquid. Another very delicate test consists in adding a few 

 drops 'of strong sulphuric acid to a small portion of the suspected 

 substance contained in a watch-glass, over which is inverted another 

 watch-glass moistened with yellow sulphide of ammonium. If cyanogen 

 is present the sulphuric acid is set free under the form of hydrocyanic 

 acid, and this with the sulphide of ammonium forms sulphocyanide of 

 ammonium (NH 4 , CyS 2 ). Excess of sulphide of ammonium must now 

 be got rid of by heating the upper watch-glass till quite dry, at a 

 temperature not exceeding that of boiling water. The addition to it 

 when cold of a drop of a dilute solution of sesquichloride of iron 

 causes the production of an intense red colour (sulphocyanide of iron). 

 This mode of detecting cyanogen may be adapted to the two preceding 

 tests, the upper watchglass being of course in the one case moistened 

 with solution of nitrate of silver, and in the other with the mixed 

 solutions of the salts of iron. In endeavouring to detect the presence 

 of hydrocyanic acid, the peculiar odour of the faintest trace of that 

 substance should ever be remembered as a valuable aid. 



Cyanogen and oxygen form no les than six compounds, all having the 

 same per-centage composition but differing markedly, and some con- 

 siderably, from each other. It will be convenient to describe them in 

 separate articles. [CYAMELIDE ; CYANIC ACID ; CYANILIC ACID ; CYA- 

 NURIC ACID ; FULMINIC ACID ; FULMINUBIC ACID.] Their relation to 

 each other may be thus expressed : 



Cyanuric acid . 

 Cyanilic acid 

 Fulminuric acid 

 Fulminic acid 

 Cyanic acid . 

 Cyamelide . 



C,H 3 NjO, = 3HO, C,N,O., 

 C,H 3 N 3 O, = SHO, C B N,0 3 

 C,H,N,O, = HO, C 6 H,N H 

 C 4 H,N,0 4 = 2HO, C.NjOj 

 C,!I N O, = HO, C 2 N O 

 C,H N O 3 = UN, C,0, 



= 3(HO, CyO) 

 = 3(HO, CyO) 

 = 3(HO, CyO) 

 = 2(HO, CyO) 

 = (HO, CyO) 

 = (HO, CyO) 



Cyanogen and nitrogen. [CYANAMIDE.] 



Cyanogen and chlorine form three isomeric compounds, the first 

 gaseous, the second liquid, and the third solid. 



Gaseous chloride of cyanogen (CyCl) is obtained by passing chlorine 

 gas into strong hydrocyanic acid, or by conveying chlorine over moist 

 cyanide of mercury excluded from the light. It may be collected over 

 mercury. 



This compound is a colourless gaseous body, extremely pungent, and 

 soluble in water, alcohol, and ether. At zero it forms a colourless 

 crystalline mass, and this at 5 melts into a liquid which boils at 11. 

 When subjected to pressure of four atmospheres it assumes a liquid 

 form ; and if long kept it is converted into the solid chloride. It is 

 composed of 1 equivalent of chlorine 35'5 -I- 1 equivalent of cyanogen 

 26 = 61-5. Spec, grav., 2'124. 



Liquid chloride of cyanogen (Cy,Clj) is produced when cyanide of 

 mercury is exposed to the action of chlorine in direct sunlight. It is 

 a liquid, boiling at 61 Fahr., and solidifying to a mass of crystals at 

 19. Equivalent, 123. 



Solid chloride of cyanogen, chlorocyanic acid (Cy 3 Cl 3 ). This compound 

 is obtained when anhydrous hydrocyanic acid is exposed to chlorine gas 

 acted upon by the sun's rays ; hydrochloric acid being also formed. It 

 has the form of long colourless needles, which have a powerful and dis- 

 agreeable odour. The crystals fuse at 284, and sublime unaltered at 

 a higher temperature. It dissolves in alcohol and ether without decom- 

 posing ; but when heated with water it is decomposed into cyanuric 

 and hydrochloric acids. It was probably owing to the formation of 

 these acids that chloride of cyanogen was originally supposed to possess 

 acid properties ; and hence the name of chlorocyanic acid. It may be 

 considered as composed of 3 equivalents of chlorine 10671 + 78 = 

 18471. Vapour density, 6'39. 



Cyanogen and bromine, and 



Cyanogen and iodine, form solid combinations. They are obtained 

 on distilling cyanide of mercury with bromine or iodine. 



Cyanogen and itdphur form a bisulphide (CyS,). This substance 

 cannot be obtained in the free state. In its combinations it partakes of 

 the nature of cyanogen itself, forming compounds in the same manner 

 as an elementary body. For this reason it is usually considered to be a 

 compound radical, and is called ttilphocyanogen ; its symbol as such is 

 (Scy). The salts that it forms with the metals very much resemble in 

 constitution the corresponding compounds with cyanic acid, the oxygen 

 in the latter being replaced by sulphur. 



Hydrosulphocyanic acid (HCyS s ), or sulpJiocyanide of hydrogen 

 (H, Scy), may be regarded as hydrated cyanic acid (HO, CyO), in which 

 the oxygen is substituted by sulphur, and may be written thus, 



B B 



