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 the formation of nitriles from potassium cyanide, and of isonitriles from silver cyanide by the assumption that unstable addition products are formed, the nature of which depends on the relative state of unsaturation of the carbon and nitrogen atoms under the varying conditions:-

that is, when the metal is highly electro-positive the carbon atom is the more unsaturated, the addition takes place on the carbon atom, and nitriles are produced. The same type of reaction occurs when the metal is relatively electro-positive to the added radical, for example, with ethyl isocyanide and acetyl chloride (see above); compare also AgNC→AgN(:Cl·COCH3)C→AgCl+CH3COCN. On the other hand, when there is but little electro-chemical difference between the radical of the cyanide and that of the reacting compound then the nitrogen atom is the more unsaturated element and isonitriles are produced. This explanation also accounts for the formation of nitriles by the diazo reaction, thus:—

C6H5N2Cl+CuNC→CuN:C·Cl·N2·C6H5→CuCl+ N⫶C·N2·C6H5→C6H5→CN+N2.

Detection.—The metallic cyanides may be detected by adding ferrous sulphate, ferric chloride, and hydrochloric acid to their solution, when a precipitate of Prussian blue is produced; if the original solution contains free acid it must be neutralized by caustic potash before the reagents are added. As an alternative test the cyanide may be decomposed by dilute hydrochloric acid, and the liberated hydrocyanic acid absorbed in a little yellow ammonium sulphide. The excess of reagent is removed by evaporation and a small quantity of a ferric salt added, when a deep red colour is produced. Silver nitrate gives a white precipitate with cyanides, soluble in excess of potassium cyanide. The amount of hydrocyanic acid in a solution may be determined by adding excess of caustic potash and a small quantity of an alkaline chloride, and running into the dilute solution standard silver nitrate until a. faint permanent turbidity (of silver chloride) is produced, that is, until the reaction, 2KNC+AgNO3＝KAg(NC)2+KNO3, is completed.

See R. Robine and M. Lengler, The Cyanide Industry, 1906 (Eng. trans. by J. A. Le Clerc); W. Bertelsmann, Die Technologie der Cyanverbindungen, 1906.

Pharmacology, Therapeutics and Toxicology of Hydrocyanic Acid.—The pharmacopoeia preparations of this acid are a 2% solution, which is given in doses of from two to six minims, the tinctura chloroform et morphinae composita, which contains a half-minim of this solution in each ten minims, and the aqua laurocerasi, which owes its virtues to the presence of this acid, and is of inconstant strength, besides being superfluous. The acid is also the active ingredient of the preparations of Virginian Prune, to which the same strictures apply.

PRUTZ, HANS (1843– ), German historian, son of Robert Eduard Prutz (1816–1872), the essayist and historian; was born at Jena on the 20th of May 1843, and was educated at the universities of Jena and Berlin. In 1865 appeared his monograph on Henry the Lion, duke of Saxony and Bavaria, which was followed by three volumes on the emperor Frederick Barbarossa (Kaiser Friedrich I., Danzig, 1871–1874). Meanwhile from 1863 to 1873 he was teaching in secondary schools. In 1874 he received a government commission to undertake explorations in Syria, particularly at Tyre, and as a result he published in 1876 Aus Phönicien, a collection of historical and geographical sketches. In the same year appeared his first work on the Crusades, Quellenbeiträge zur Geschichte der Kreuzzüge, and a series of monographs on the same subject culminated in 1883 in the notable Kulturgeschichte der Kreuzzüge. Then turning to a wider theme Prutz contributed to Oncken's university history the two volumes on the political history of Europe during the middle ages (Staatengeschichte des Abendlandes im Mittelalter, Berlin, 1885–1887). In 1888 he reverted to a subject which he had touched upon in his Geheimlehre uud Geheimstatuten des Tempelherrenordens (Danzig, 1879), and wrote the history of the rise and fall of the Templars (Entwickelung und Untergang des Tempelherrenordens), which is noticed in the article. His Preussische Geschichte (4 vols., Stuttgart, 1899–1902), which is perhaps his most notable work, is an attempt to apply scientific rather than patriotic canons to a subject which has been mainly in the hands of historians with a patriotic bias. He also wrote Aus des Grossen Kurfürsten letzten Jahren (Berlin, 1897) and Bismarcks Bildung, ihre Quellen und ihre Äusserungen (Berlin, 1904). In 1902 Prutz resigned the chair of history in the university of Königsberg, which he had held since 1877, and took up his residence at Munich.

 PRUTZ, ROBERT EDUARD (1816–1872), German poet and prose writer, was born at Stettin on the 30th of May 1816. He studied philology, philosophy and history at Berlin, Breslau and Halle, and in the last-named became associated, after taking his degree, with Arnold Ruge in the publication of the Hallesche Jahrbücher. Subjected on account of his advanced political views to police surveillance, he removed to Jena, where, on the strength of an excellent monograph, Der Göttinger Dichterbund (1841), he hoped to obtain an academic appointment. He was, however, expelled from the town for offending against the press laws, and it was not until 1846 that he received permission to lecture in Berlin. From 1849 to 1859 he was extra-ordinary professor of literature at Halle, but retired in 1859 to Stettin, where he died on the 21st of June 1872.

Prutz belonged to the group of political poets who dominated German literature between 1841 and 1848; hispoems are more conspicuous for their liberal tendency than their poetry. Among them may be mentioned Ein Märchen (1841); Gedichte (1841); Aus der Heimat (1858); Neue Gedichte (1860); Herbstrosen (1865); Buch der Liebe (1869). Among his novels are noteworthy, Das Engelchen (1851) and Der Musikauteuturm (1855); Much more important are his contributions to literary history and criticism: Vorlesungen über die Geschichte des deutschen Theaters (1847); Ludwig Holberg (1857); Die deutsche Literatur der Gegenwart (1859), and Menschen und Bücher (1862). Prutz also Wrote some dramas of little merit.

PRYNNE, WILLIAM (1600–1669), English parliamentarian, son of Thomas Prynne by Marie Sherston, was born at Swainswick near Bath in 1600. He was educated at Bath Grammar School, matriculated at Oriel College, Oxford, in 1618, obtained his B.A. in 1621, was admitted a student of Lincoln's Inn the same year, and was called to the Bar in 1628. He was Puritan