PHENAZINE (Azophenylene), C12H5N2  , in organic chemistry, the parent substance of many dyestuffs, e.g. the eurhodines, toluylene red, indulines and safranines . It is a dibenzoparadiazine having the formula given below . It may be obtained by distilling barium azobenzoate (A . Claus, Ber., 1873, 6, p . 723); by passing aniline vapour over lead oxide, or by the oxidation of dihydrophenazine, which is prepared by heating pyrocatechin with orthophenylene diamine (C . Ris, Ber., 1886, 19, p . 2206) . It is also formed when ortho-amipodiphenylamine is distilled over lead peroxide (O . Fischer and E . Hepp) . It crystallizes in yellow needles which melt at 1710 C., and are only sparingly soluble in alcohol . Sulphuric acid dissolves it, forming a deep-red solution .

The more complex phenazines, such as the naphthophenazines, naphthazines and naphthotolazines, may be prepared by condensing ortho-diamines with ortho-

quinones (O . Hinsberg, Ann., 1887, 237, p . 340); by the oxidation of an ortho-diamine in the presence of a-naphthol (0 . Witt), and by 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 . 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 metaaminophenols with phthalic anhydride in the presence of sulphuric acid . Their salts are fine red dyes . By the entrance of amino or hydroxyl groups into the molecule .

PHENOMENON (Gr . 4,atvo..cevov, a thing seen, from cbaiveuOat, dyestuffs are formed . The mono-amino derivatives or eurhodines I to appear in

ordinary language a thin rocess event &c., are obtained when the arvlmonamines are condensed with ortho- )' g g °' p ' ' amino zo compounds; by condensing quinone dichlorimide or I observed by the senses . Thus the rising of the sun, a thunderpara-nitrosodimethyl aniline with monamines containing a free I 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 (ra aura) 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 noumenon (q.v.) or object of pure thought, but the thing-in-itself as it appears to the mind in sensation (see especially KANT; and METAPHYSICS) . In this sense the subjective character is of prime importance . Among derivative terms are " Phenomenalism" and "Phenomenology." Phenomenalism is either (I) 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-inthemselves." " 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 .