Page:EB1911 - Volume 21.djvu/385

Rh tends to paralyse the action of the cardiac muscle. Upon the bodily heat it exercises a marked effect, decreasing the action of the heat-producing centre as well as increasing the dissipation of heat, and thus causing a marked fall in temperature. In toxic doses the blood becomes dark and blackish from the formation of methaemoglobin, and the urine is changed in colour from the passage of altered blood. The chief therapeutic use of phenacetin is as an antineuralgic, and it is of service in migraine, rheumatism of the sub-acute type, intercostal neuralgia and locomotor ataxia.

  PHENACITE, a mineral consisting of beryllium orthosilicate, Be2SiO4, occasionally used as a gem-stone. It occurs as isolated crystals, which are rhombohedral with parallel-faced hemihedrism, and are either lenticular or prismatic in habit: the lenticular habit is determined by the development of faces of several obtuse rhombohedra and the absence of prism faces (the accompanying figure is a plan of such a crystal viewed along the triad, or principal, axis). There is no cleavage, and the fracture is conchoidal. The hardness is high, being 7 – 8; the specific gravity is 2.98. The crystals are sometimes perfectly colourless and transparent, but more often they are greyish or yellowish and only translucent; occasionally they are pale rose-red. In general appearance the mineral is not unlike quartz, for which indeed it had been mistaken; on this account it was named, by N. Nordenskiöld in 1833, from Gr.  (a deceiver).

Phenacite has long been known from the emerald and chrysoberyl mine on the Takovaya stream, near Ekaterinburg in the Urals, where large crystals occur in mica-schist. It is also found with topaz and amazon-stone in the granite of the Ilmen mountains in the southern Urals and of the Pike’s Peak region in Colorado. Large crystals of prismatic habit have more recently been found in a felspar quarry at Kragerö in Norway. Framont near Schirmeck in Alsace is another well-known locality. Still larger crystals, measuring 12 in. in diameter and weighing 28 ℔, have been found at Greenwood in Maine, but these are pseudomorphs of quartz after phenacite.

For gem purposes the stone is cut in the brilliant form, of which there are two fine examples, weighing 43 and 34 carats, in the British Museum. The indices of refraction (=1.6540, =1.6527) are higher than those of quartz, beryl or topaz; a faceted phenacite is consequently rather brilliant and may sometimes be mistaken for diamond.

 PHENACODUS, one of the earliest and most primitive of the ungulate mammals, typifying the family Phenacodontidae and the sub-order Condylarthra. The typical Phenacodus primaevus, of the Lower or Wasatch Eocene of North America, was a relatively small ungulate, of slight build, with straight limbs each terminating in five complete toes, and walking in the digitigrade fashion of the modern tapir. The middle toe was the largest, and the weight of the body was mainly supported on this and the two adjoining digits, which appear to have been encased in hoofs, thus foreshadowing the tridactyle type common in perissodactyle and certain extinct groups of ungulates. The skull was small, with proportionately minute brain; and the arched back, strong lumbar vertebrae, long and powerful tail, and comparatively feeble fore-quarters all proclaim kinship with the primitive creodont Carnivora (see ), from which Phenacodus and its allies, and through them the more typical Ungulata, are probably derived. All the bones of the limbs are separate, and those of the carpus and tarsus do not alternate; that is to say, each one in the upper row is placed immediately above the corresponding one in the row below. The full series of forty-four teeth was developed; and the upper molars were short-crowned, or brachyodont, with six low cones, two internal, two intermediate and two external, so that they were of the typical primitive bunodont structure. In habits the animal was cursorial and herbivorous, or possibly carnivorous.

In the Puerco, or Lowest Eocene of North America the place of the above species was taken by Euprotogonia puercensis, an animal only half the size of Phenacodus primaevus, with the terminal joints of the limbs intermediate between hoofs and claws, and the first and fifth toes taking their full share in the support of the weight of the body. These two genera may be regarded as forming the earliest stages in the evolution of the horse, coming below Hyracotherium (see ).

As ancestors of the Artiodactyle section of the Ungulata, we may look to forms more or less closely related to the North American Lower Eocene genera Mioclaenus and Pantolestes, respectively typifying the families Mioclaenidae and Pantolestidae. They were five-toed, bunodont Condylarthra, with a decided approximation to the perissodactyle type in the structure of the feet. A third type of Condylarthra from the North American Lower Eocene is represented by the family Meniscotheriidae, including the genera Meniscotherium and Hyracops. These, it is suggested, may have been related to the ancestral Hyracoidea. Teeth and jaws probably referable to the Condylarthra have been obtained in European early Tertiary formations. All Ungulata probably originated from Condylarthra.

See H. F. Osborn, Skeleton of Phenacodus primaevus; comparison with Euprotogonia, Bull. Amer. Mus. x. 159.

 PHENANTHRENE, C14H10, a hydrocarbon isomeric with anthracene, with which it occurs in the fraction of the coal tar distillate boiling between 270°–400° C. It may be separated from the anthracene oil by repeated fractional distillation, followed by fractional crystallization from alcohol (anthracene being the less soluble), and finally purified by oxidizing any residual anthracene with potassium bichromate and sulphuric acid (R. Anschutz and G. Schultz, Ann., 1879, 196, p. 35); or the two hydrocarbons may be separated by carbon bisulphide, in which anthracene is insoluble. It is formed when the vapours of toluene, stilbene, dibenzyl, ortho-ditolyl, or coumarone and benzene are passed through a red-hot tube; by distilling morphine with zinc dust; and, with anthracene, by the action of sodium on ortho-brombenzyl bromide (C. L. Jackson and J. F. White, Amer. Chem. Jour., 1880, 2, p. 391). It crystallizes in colourless plates or needles, which melt at 99° C. Its solutions in alcohol and ether have a faint blue fluorescence. When heated to 250° C. with red phosphorus and hydriodic acid it gives a hydride C14 H24. It is nitrated by nitric acid and sulphonated by sulphuric acid. With picric acid it forms a sparingly soluble picrate, which melts at 145° C. On the condition of phenanthrene in alcoholic solution see R. Behrend, ''Zeit. phys.'' Chem., 1892, 9, p. 405; 10, p. 265. Chromic acid oxidizes phenanthrene, first to phenanthiene-quinone, and then to diphenic acid, HO2C·C6H4·C6H4·CO2H.

Phenanthrene-quinone, [C6H4]2[CO]2, crystallizes in orange needles which melt at 198° C. It possesses the characteristic properties of a diketone, forming crystalline derivatives with sodium bisulphite and a dioxime with hydroxylamine. It is non-volatile in steam, and is odourless. Sulphurous acid reduces it to the corresponding dihydroxy compound. It combines with ortho-diamines, in the presence of acetic acid, to form phenazines.

On the constitution of phenanthrene see. § Organic.

 PHENAZINE (Azophenylene), C12H8N2,, 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-aminodiphenylamine is distilled over lead peroxide (O. Fischer and E. Hepp). It crystallizes in yellow needles which melt at 171° 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 -naphthol (O. Witt), and by