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 the decomposition of ortho-anilido-(-toluidido- &c.)-azo compounds with dilute acids. If alkyl or aryl-ortho-diamines be used azonium bases are obtained. The azines are mostly yellow in colour, distil unchanged and are stable to oxidants. They add on alkyl iodides readily, forming alkyl azonium salts.

By the entrance of amino or hydroxyl groups into the molecule dyestuffs are formed. The mono-amino derivatives or eurhodines are obtained when the arylmonamines are condensed with ortho-amino -zo compounds; by condensing quinone dichlorimide or para-nitrosodimethyl aniline with monamines containing a free, para position, or by oxidizing ortho-hydroxydiaminodiphenylamines (R. Nietzki, Ber., 1895, 28, p. 2976; O. Fischer, ibid., 1896, 29, p. 1874) The are yellowish-red solids, which behave as weak bases, their salts undergoing hydrolytic dissociation in aqueous solution When heated with concentrated hydrochloric acid the amino group is replaced by the hydroxyl group and the phenolic eurhodols are produced.

The symmetrical diaminophenazine is the parent substance of the important dyestuff toluylene red or dimethyldiaminotoluphenazine It is obtained by the oxidation of orthophenylene diamine with ferric chloride; when a mixture of para-aminodimethylaniline and meta-toluylenediamine is oxidized in the cold, toluylene blue, an indamine, being formed as an intermediate product and passing into the red when boiled; and also by the oxidation of dimethylparaphenylene diamine with metatoluylene diamine. It crystallizes in orange-red needles and its alcoholic solution fluoresces strongly. It dyes silk and mordanted cotton a fine scarlet. It is known commercially as neutral red. For the phenazonium salts see.

Phenazone is an isomer of phenazine, to which it bears the same relation that plienanthrene bears to anthracene. It is formed by reducing diortho-dinitrodiphenyl with sodium amalgam and methyl alcohol, or by heating diphenylene-ortho-dihydrazine with hydrochloric acid to 150° C. It crystallizes in needles which melt at 156° C. Potassium permanganate oxidizes it to pyridazine tetracarboxylic acid.

PHENOLPHTHALEIN, in organic chemistry, a compound derived from phthalophenone, or diphenyl phthalide (formula l), the anhydride of triphenyl-carbinol-ortho-carboxylic acid, which is obtained by condensing phthalyl chloride with benzene in the presence of aluminium chloride. The phthaleins are formed from this anhydride by the entrance of hydroxyl or amino groups into the two phenyl residues, and are prepared by condensing phenols with phthalic anhydride, phenol itself giving rise to phenolphthalein (formula II.) together with a small quantity of fluorane (formula III.), whilst resorcin under similar conditions yields (q.v.). The phthaleins on reduction yield phthalines, which are derivatives of triphenylmethane carboxylic acid, these reduction products are colourless and may be regarded as the leuco-compounds of the phthaleins, thus phenolphthalein itself gives phenolphthalein (formula IV.). Dehydrating agents usually convert the phenolphthalein’s into anthraquinone derivatives.

Phenolphthalein is obtained when phenol and phthalic anhydride are heated with concentrated sulphuric acid. It crystallizes in colourless crusts and is nearly insoluble in water, but dissolves in dilute solutions of the caustic alkalis with a fine red colour, being re precipitated from these solutions by the addition of mineral acid It dissolves in concentrated caustic alkalis to a colourless solution which probably contains salts of a non-quinonoid character. This difference in behaviour has led to considerable discussion (see H. Meyer, Monats., 1899, 20, p 337; R. Meyer, Ber., 1903, 36, p. 2949, A. G. Perkin and Green, Jour. Chem. Soc., 1904, p. 398). On fusion with caustic alkali, phenolphthalein yields benzoic acid and para-dihydroxybenzophenone, which shows that in the original condensation the phthalic acid residue has taken the para position to the hydroxyl groups of the phenol.

Fluorane is a product of the condensation of the phthalic acid residue in the ortho position to the hydroxyl groups of the phenol, anhydride formation also taking place between these hydroxyl groups. It dissolves in concentrated sulphuric acid with a yellowish green fluorescence. The rhodamines, which are closely related to the phthaleins, are formed by the condensation of the alkyl meta-aminophenols with phthalic anhydride in the presence of sulphuric acid. Their salts are fine red dyes.

 PHENOMENON (Gr., a thing seen, from , to appear), in ordinary language a thing, process, event, &c., observed by the senses. Thus the rising of the sun, a thunder storm, an earthquake are natural “phenomena.” From this springs the incorrect colloquial sense, something out of the common, an event which especially strikes the attention; hence such phrases as “phenomenal” activity. In Greek philosophy phenomena are the changing objects of the senses as opposed to essences which are one and permanent, and are therefore regarded as being more real, the objects of reason rather than of senses which are “bad witnesses.” In modern philosophy the phenomenon is neither the “thing-in-itself,” nor the  (q.v.) or object of pure thought, but the thing-in-itself as it appears to the mind in sensation (see especially ; and ). In this sense the subjective character is of prime importance. Among derivative terms are “Phenomenalism” and “Phenomenology,” Phenomenalism is either (1) the doctrine that there can be no knowledge except by phenomena, i.e. sense-given data, or (2) the doctrine that all known things are phenomena, i.e. that there are no “things-in-themselves.” “Phenomenology” is the science of phenomena: every special science has a special section in which its particular phenomena are described. The term was first used in English in the 3rd edition of the ''Ency. Brit''. in the article “Philosophy” by J. Robison. Kant has a special use of the term for that part of the Metaphysic of Nature which considers motion and rest as predicates of a judgment about things.

 PHERECRATES, Greek poet of the Old Attic Comedy, was a contemporary of Cratinus, Crates and Aristophanes. At first an actor, he seems to have gained a prize for a play in 438 The only other ascertained date in his life is 420, when he produced his play The Wild Men. Like Crates, whom he imitated, he abandoned personal satire for more general themes, although in some of the fragments of his plays we find him attacking Alcibiades and others. He was especially famed for his inventive imagination, and the elegance and purity of his diction are attested by the epithet (most Attic) applied to him by Athenaeus and the sophist Phrynichus. He was the inventor of a new metre, called after him Pherecratean, which frequently occurs in the choruses of Greek tragedies and in Horace.

A considerable number of fragments from his 16 (or 13) plays has been preserved, collected in T. Kock, Comicorum Atticorum Fragmenta, 1. (1880), and A. Meineke, Poetarum Comicorum Graecorum Fragmenta (1855).

 PHERECYDES OF LEROS, Greek mythographer, fl. c. 454 He is probably identical with Pherecydes of Athens, although the two are distinguished by Suidas (also by T. Lipsius, Quaestiones logographicae, 1886). He seems to have been born in the island of Leros, and to have been called an Athenian because he spent the greater part of his life and wrote his great work there. Of his treatises, On Leros, On Iphigeneia, On the Festivals of Dionysus, nothing remains; but numerous fragments of his genealogies of the gods and heroes, variously called , in ten books, written in the Ionic dialect, have been preserved (see C. W. Müller’s Frag. hist. graec., vol. i. pp. xxxiv., 70). He modified the legends, not with a view to rationalizing them, but rather to adjust them to popular beliefs. He cannot, therefore, be classed with Hecataeus, whose method was far more scientific.

See C. Lütke, Pherecydea (diss. Göttingen, 1893); W. Christ, Geschichte der griechischen Litteratur (1898); and specially H. Bertsch, Pherekydeische Studien (1898).

 PHERECYDES OF SYROS, Greek philosopher (or rather philosophical theologian), flourished during the 6th century He was sometimes reckoned one of the Seven Wise Men, and is said to have been the teacher of Pythagoras. With the possible 