Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/567

CYANOGEN COMPOUNDS. CHEMISTRY 555 Other double cyanides do not decompose in this man ner by the action of mineral acids ; the heavy metal can not be detected by its ordinary reagents, and no HCy is evolved. Thus the double cyanide of potassium and iron, 4KCy,FeCy 2 , when acted on by acids exchanges its potas sium for hydrogen, but the iron is not removed : K 4 FeCy 6 + 4HC1 = H 4 FeCy 6 + 4KC1 . Potassium ferrocyanide. Hydroferrocyanic acid. Thus the group FeCy 6 is regarded as an acid radicle (ferrocyanogeii), and a large number of its salts (ferro cyanides) are known. In the same manner we have Ferricyanides M 6 Fe 2 Cy 12 = 6M Cy. Fe 2 Cy 6 Cobaltocyanides M 4 CoCy 6 = 4M Cy. CoCy 2 Dobalticyanides M 6 Co 2 Cy 12 = GM Cy. Co 2 Cy 8 Siangan ocyanides M 4 MnCy 6 = 4M Cy.MnCy 2 Manganicyanides M 6 Mn. 2 Cy 12 = 6M Cy. Mn 2 Cy g Chromoc} r anides M 4 CrCy 6 = 4M Oy. CrCy 2 Chromicyanides M 6 Cr,Cy 12 = 6M Cy.Cr 2 Cy 6 Platinocyanides M 2 PtCy 4 = 2M Cy.PtCy 2 Palladiocyanides M 2 PdCy 4 =2M Cy.PdCy 2 Of these compounds the most important are the ferro- cyanides and ferricyanides of potassium. Potassium ferrocyanide (known commonly as yellow prussiate of potash}, is prepared on the large scale by fusing refuse animal matter, such as horn parings, leather scraps, &c., with crude potassium carbonate and iron filings. This salt is also formed when a ferrous salt is added to a solution of potassium cyanide 6KCy + FeS0 4 = K 4 FeCy 6 + K 2 SO 4 . Potassium ferrocyanide crystallizes in large pale yellow crystals belonging to the quadratic system, and having the composition K 4 FeCy 6 , 30H 2 . Solutions of ferric salts produce in an aqueous solution of potassium ferrocyanide a deep blue precipitate of ferric ferrocyanide or Prussian blue : 3K 4 FeCy 6 + 2Fe 2 Cl 6 = 2Fe 2 Cy (3 .3FeCy 2 + 12KC1 . Prussian blue. Soluble ferrocyanides are thus a delicate test for the pre sence of ferric salts ; and conversely, ferric salts are used to detect ferrocyanides, and also cyanides by the simultaneous addition of a ferrous salt (Scheele s test for prussic acid). Potassium ferricyanide (or red prussiate of potash) is prepared by passing chlorine into a solution of the ferro cyanide : 2K 4 FeCy 6 + C1 2 = K 6 Fe 2 Cy 12 + 2KC1 Ferricyanide. The ferricyanide forms large prismatic crystals of a dark red colour soluble in water. Ferric salts give a brown coloration with ferricyanides, while ferrous salts give a blue precipitate of TurnbulVs blue (Fe 5 Cy 12 + Aq). Nitroprussides are salts of the general formula M 2 Fe"Cy 5 NO obtained by the action of nitric acid upon ferro- and ferri-cyanides. Cyanides of Hydrocarbon Radicles. The compounds the union of cyanogen with hydrocarbon of the utmost interest and importance on their metameric modifications. Thus we formed by radicles are account of have C 2 H 6 Ethane. C 2 H 5 .CN Cyanethane= Ethyl cyanide. C 2 H 4 ".(CN) 2 Ethene cyanide. On developing the graphic formulas of one of these cyanides containing a monad radicle, taking for brevity the simplest case, viz., CH 3 .CX, methyl cyanide, it will be seen that two metamerides are possible (see also p. 551): H H H C N=C H H C In the one compound the carbon of the radicle is in combination with the nitrogen of the cyanogen. In the other compound the same carbon atom is in combination with the carbon of the cyanogen. Two such metameric series are actually known, one (cyanides or nitriles) being formulated as hydrocarbon derivatives^ and the other (isocyanides or carbamines) as ammonia derivatives or amines (see p. 553); thus (representing the monad radicle by R )- C IT H H H Methane. c N " E Cyanide or nit rile. H Ammonia. N C" R Isocyanide or Carbamine. In accordance with what has been previously said con cerning isomeric bodies (p. 551), these two series ex hibit different behaviour under the action of the same reagent. For instance, the following equations show the ultimate action of water on them : Cyanides. Isocyanides. ( M " n ) K x , (C" ( H ( TT ^ 1 TJ/ i O/~>TT ~ru i r< ( It + /Uxl 2 IN rl;j + O 0" HO E+20Hj K|H+ (COOH Acid. Amine. Formic acid. In accordance with these reactions cyanides or nitriles can be produced by the action of dehydrating agents on the ammonium salts of the corresponding acids H.CO(ONH 4 ) - 20H 2 = H.CN = (CH) "N Ammonium formate. Hydrogen cyanide. Formonitrile. CH 3 .CO(ONH 4 ) - 20H 2 = CH 3 .CN = (C 2 H S ) "N Ammonium acetate. Methyl cyanide. Acetonitrile. C 2 H 5 .CO(ONH 4 ) - 20H 2 = C 2 H 5 .CN = (C 3 H 5 ) "N Ammonium propionate. Propyl cyanide. Propionitrile. C 6 H 5 .CO(ONH 4 ) - 20H 2 = C 6 H 5 .CN = (C 7 H 5 ) "N Ammonium benzoate. Phenyl cyanide. Benzonitrile. The action of water upon nitriles thus gives rise to the formation of an acid containing the same number of carbon atoms as the nitrile ; the radicle remaining unchanged, we may consider that in these reactions cyanogen (CN) is converted into carboxyl (COOH) R .CN + 20H 2 = NH 3 + R .COOH . It has been further stated that both the nitriles and organic acids can be formulated as hydrocarbon derivatives in the former the H of the radicle being replaced by (ON) , and in the latter by (COOH) . Starting then with the cyanide of a hydrocarbon radicle, we get by the action of water an acid containing one atom of carbon more than the hydrocarbon from which the acid is derived, and in this manner acids can be built up from their parent hydrocarbons, and the number of their contained semi- molecules of carboxyl increased ; thus H.CN H.COOH Hydrogen cyanide is converted by the action of water into Formic acid. CH 3 .CN Methyl cyanide. C 2 H 4 ".(CN) 2 Ethene cyanide. R".(CN) n CH 2 .CN.COOH Cyanacetic acid. CHg.COOH Acetic acid. C 2 H 4 ".(COOH) 2 Succinic acid. CH 2 .(COOH) Malonic acid. R - H n .(CN) n .(COOH) R - H fl .(COOH) n+: The cyanides of the hydrocarbon radicles will be again referred to when treating of the haloid ethers, of which bodies they may be considered the analogues. The

isocyanides will be treated of as amines.