Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/37

Rh P R Y P R Y 25 has just been completed. One cub. cent, of silver solution used indicates 2 milligrammes of NCH. Liebig's method lends itself particularly well for the assay ing of the medicinal acid and of cyanide of potassium. The two tests for hydrocyanic acid given above apply as they stand to solutions of the cyanides of alkali and alkaline-earth metals, but not to mercuric cyanide. In regard to all other cyanides we have only space to say that from a certain set (which includes the cobalti-cyanides and the platinum cyanides) cyanogen cannot be extracted at all as NCH (or AgNC) by any known methods. Such bodies must be identified by their own specific reactions or by elementary analysis. All cyanides are de- composed by hot concentrated sulphuric acid ; the carbon goes off as CO, the nitrogen remains as sulphate of ammonia and the metals as sulphates, which brings them within the range of the routine methods of analysis. Cyanates. These were discovered by Wb'hler. The potassium salt NCO. K is produced by the oxidation of fused cyanide, for pre- parative purposes most conveniently by Wohler's method. An intimate mixture of two parts of absolutely anhydrous prussiate of potash and one part of equally dry binoxide of manganese is heated on an iron tray until the mass has become brownish black and just begun to fuse. It is now allowed to cool and exhausted by boiling 80 per cent, alcohol. The filtrate on cooling deposits crystals of the salt NCO.K. If only an aqueous solution of this salt is wanted for immediate use, the fuse may be extracted by cold water. From this solution the cyanate of silver, NCO.Ag, or lead, (NCO) 2 Pb, can be prepared by precipitation with solutions of the respective nitrates or acetates. Hot water decomposes cyanate of potash promptly with formation of carbonates of potash and ammonia, KNCO + 2H 2 = NH 3 + KHO + C0 2. On addition of mineral acid to even the cold solution only a very little of the cyanic acid is liberated as such ; the bulk breaks up at once with effervescence, thus, NCO. H + 2H 2 = NH 3 + C0 2 + H.,0. Very interesting is the action of the solution of cyanate of potash on sulphate of ammonia ; its direct effect is the formation of cyanate of ammonia, NCO.NH 4 , but this salt almost immediately passes spontaneously into its isomer urea, which is not a cyanate at all but the amide of carbonic acid, i.e., CO(OH) 2 -2(OH) + 2NH 2 =C0^2 2. This reaction was discovered by Wohler, who thus for the first time produced an organic substance from inorganic materials, or virtually from its elements. Singularly, it is this pseudo-cyauate urea which serves as a material for making cyanic acid. When hydrochlorate of urea, HC1. CON.,H 4, is heated to 145 C. the latter behaves as if it were cyanate of ammonia : the ammonia unites with the hydrochloric acid into sal-ammoniac and the cyanic acid is set free, but imme- diately suffers polymerization into cyanuric acid, a solid tri- basic acid of the composition N 3 C 3 3 H 3, which, being difficultly soluble, can be freed from the sal-ammoniac by being washed with cold water. If perfectly anhydrous cyanuric acid be subjected to dry distillation it furnishes a distillate of (liquid) cyanic acid NCO. H, which must be condensed in a vessel surrounded by a freezing mixture. Cyanic acid has a very appreciable vapour-tension even at ordi- nary temperatures, and the least trace of its vapour makes itself felt by a characteristically violent and dangerous action on the respira- tory organs. With dry ammonia gas it unites into true cyanate of ammonia. We do not know much of its own properties, because as soon as it comes out of the freezing mixture it begins to suffer polymerization into "cyamelid" with great evolution of heat. This cyamelid is a porcelain-like mass, insoluble in all ordinary solvents and devoid of acid properties. Dry distillation reconverts it into cyanic acid. Thiocyanates. This term means bodies like cyanates, but containing sulphur instead of the oxygen of the latter. Thio- cyanates are better known, however, as sulphocyanates or sulpho- cyanides. (1) The potassium salt NCS.K is formed when cyanide of potassium is fused with sulphur or certain metallic sulphides, e.g., PbS. The usual method of preparation is to fuse together forty-six parts of dehydrated yellow prussiate of potash, seventeen of dry carbonate of potash, and thirty- two of sulphur. The fuse is exhausted with boiling alcohol and the filtered solution allowed to cool, when crystals of the salt separate out. The salt is very soluble in water with characteristically large absorption of heat. (2) The ammonium salt NCS. NH 4 can be prepared by allowing a mixture of alcohol, strong aqueous ammonia, and bisulphide of carbon to stand for a time and then warming it. Thiocarbonate of ammonium, CS 2 .(NH 4 ) 2 S, is produced first, but subsequently it gives up 2H.,S to the ammonia and becomes NCS. NH 4, which is easily obtained in crystals. The tar water obtained in the manufacture of coal-gas sometimes contains sufficient quantities of this salt to make it worth while to recover it. Both the potassium and the ammonium salt are much used as reagents, and more especi- ally as precipitants for copper and silver. Solutions of cupric salt when mixed with sulphocyanate assume the dark-brown colour of the cupric salt Cu(NCS).,, but on addition of sulphurous acid the colour disappears and a white precipitate of cuprous sulphocyanide, NCS. Cu, comes down, which, if enough of reagent was used, con- tains all the copper. If sulphocyanate is added to nitrate of silver, all the silver is precipitated as Ag. NCS, similar in appearance to the chloride and, like it, insoluble in water and in nitric acid. Upon this and the fact that sulphocyanates strike a deep red colour with ferric salts Volhard lias based an excellent titrimetric method for the determination of silver. (See SILVER.) Syntheses of Cyanogen Compounds. Synthetical organic chemistry dates from Wb'hler's discovery of the artificial formation of urea, and in the further development of this branch of the science cyano- gen has played a prominent part. (For illustrations we may refer to certain passages in the present article and in those on METHYL and on NITIIOGEX.) Hence it is worth while to enumerate briefly the synthetical method for the making of cyanogen itself. (1) Hydrocyanic acid is produced when a current of electric sparks is made to cross a mixture of acetylene, C 2 H 2, and nitrogen. (2) Cyanide of ammonium is formed when ammonia is passed over red-hot charcoal (see supra). (3) Metallic cyanides are produced when diy nitrogen gas is passed over a dry mixture of carbonate of potash or baryta and charcoal at a white heat. A similar reaction goes on spontaneously in the iron-smelting furnaces and gives rise to the formation of vapour of cyanide of potassium. (4) Sulpho- cyanide of ammonium is produced from bisulphide of carbon and ammonia, as explained above. (W. D. ) PRYNNE, WILLIAM (1600-1669), was born at Swains- wick near Bath in 1600. He was educated at Bath grammar-school, and became a commoner of Oriel College, Oxford, in 1616, taking his B.A. in 1621 ; he was ad- mitted a student of Lincoln's Inn in the same year, and in due time became a barrister. His studies led him deeply into legal and constitutional lore, and no less deeply into ecclesiastical antiquities. He was Puritan to the core, with a tenacious memory, a strength of will bordering upon obstinacy, and a want of sympathy with human nature in its manifold variety. His first book, The Per- petuity of a Regenerate Man's Estate, 1627, was devoted to a defence of one of the main Calvinistic positions, and The Unloveliness of Love-locks and Health's Sickness, 1628, were devoted to attacks upon prevailing fashions, con- ducted without any sense of proportion, and treating follies on the same footing as scandalous vices. After the dissolution of parliament in 1629 Prynne came forward as the assailant of Arminianism in doctrine and of ceremonialism in practice, and thus drew down upon himself the anger of Laud. Histrio-mastijc, published in 1633, was a violent attack, not upon the special im- moralities of the stage of Prynne's day but upon stage- plays in general, in Avhich the author laid himself open to the charge of assailing persons in high position, in the first place by pointing out that kings and emperors who had favoured the drama had been carried off by violent deaths, which assertion might easily be interpreted as a warning to the king, and in the second place by applying a dis- graceful epithet to actresses, which, as Henrietta Maria was taking part in the rehearsal of a ballet just as the sheet containing the offensive words was passing through the press, was supposed to apply to the queen. On 17th February 1634 Prynne was sentenced by the Star Chamber to be imprisoned and also to be fined 5000, expelled from Lincoln's Inn, rendered incapable of returning to his pro- fession, degraded from his degree in the university of Oxford, and set in the pillory, where he was to lose both his ears. On 7th May Prynne was placed in the pillory and lost his ears. The rest of the sentence, with the exception of the clause relating to the payment of the fine, was carried out. A sharp letter written by him to Laud criticizing his arguments at the trial was made the founda- tion of a fresh charge. Prynne, however, got the letter into his hands and tore it up. Though he was again brought before the Star Chamber, on llth June, no addi tional penalty was inflicted on him. There is no reason to suppose that his punishment was unpopular. In 1637 he was once more in the Star Chamber, together with Bastwick and Burton. In A Divine Tragedy lately acted XX. 4