Page:EB1911 - Volume 22.djvu/711

From Wikisource
Jump to navigation Jump to search
This page needs to be proofread.
695
PYROPE—PYROPHYLLITE

yellow colour and blue fluorescence. Fisetin or 3- 3' -4'-trioxyflavonol, Cl, ,H10O¢, occurs in the wood of Quebracho colorado, and can be obtained by heating fustic with dilute acids. It crystallizes in pale yellow needles. In dilute alcoholic alkalis it shows adark green fluorescence. On fusion with caustic alkalis it yields phloroglucin, resorcin and protocatechuic acid, whilst if air be passed through its alcoholic solution it yields protocatechuic acid and resorcin. It is obtained synthetically from 2-oxy-3-4-dimethoxy-4-ethoxy-chalkone. The various steps in this synthesis are shown below, since the method employed is applicable to other members of the group. C H -

2 5 C¢;H3~COCH3+0HC-C5H3(OCH3)2-9

H

c H

2 5 CSH3-CO-CH:CH-C6H3(OCH3)9

no J/

o o

CQHSOKY cH~c, n, ,<ocn, >2<-c2H, o// CH~C6H3(OCH3)g c=No M cn

/co/ H co/ 2

O O

c2H.q// CH'CeH3(0CH3)z e H // g-canon).

co con

)c0/ Co/

This structure of the fisetin molecule was confirmed by Herzig (Monats., 1891, 12, p. 177), who showed that the tetra ethyl ether of fisetin on hydrolysis with alcoholic potash gave diethylprotocatechuic acid and diethyltisetol, the latter on oxidation yielding ethyl-B-resorcylic acid, which had been previously obtained by oxidizing res ace top hen one ethyl ether. Luleolin or 1-3-3'~4'-tetroxyflavone, C|5H10O¢, is found in the weld obtained from Reseda luteolo. It crystallizes in small yellow needles, which dissolve in solutions of the caustic alkalis with a bright yellow colour. On fusion with caustic alkalis it yields hloroglucin and protocatechuic acid. It is obtained synthetically from I-3-3'-4'-tetramethoxy-f lava none by bromination, the tribromo-compound being decomposed by the successive use of alcoholic potash and concentrated hydriodic acid. Quercetin or 1~3-3'-4'-tetroxyflavonol, C15H,0O1, is a decomposition product of quercitrin rind, and is found in many plants. It is obtained by the hydrolysis of quercitrin with dilute sulphuric acid. It is a pale yellow crystalline powder. Alcohol hydrolyses it to protocatechuic acid and phloroglucin. It is prepared synthetically from 2-hydroxy-3-4-4'-6'-tetramethoxy-chalkone. Rhamnetin, C,5H9O5-OCH3, the mono methyl ether, is a pale yellow powder. Rhonznazin, C15Hf, O5(OCH3)2, the dimethyl ether, crystallizes in yellow needles. Morin or I-3-2'~4'-tetroxyflavonol, C15H10O1, occurs in the wood of Aulscorpis integrifolia, and crystallizes in long yellow needles, which on fusion with caustic alkali decompose into phloroglucin, resorcin and oxalic acid. On reduction with sodium amalgam in alkaline solution it yields phloroglucin and, B-resorcylic acid. It yields a tetra methyl ether and a penta-acetate. It has been synthesized from I-3-2'-4'-tetramethoxy flayanone by converting this into its isonitroso compound, which yields morin trim ethyl ether on hydrolysis by sulphuric acid. Myricetin or 1-3~3'~4 -5'-penta-oxy flavonol, CMHWOS, found in the rind of Myrica nagi and also in Sicilian sumach, crystallizes in yellow needles which dissolve with a green colour in dilute alkalis. On fusion with caustic alkalis it yields gallic acid and phloroglucin. The parent substance of the group, namely chroman (annexed formula), was obtained by v. Braun and A.

H2-Cl-lg Steindorff in 1905 (Ben, 38, p. 850) by diazotizing C@Hi I . ortho-amino—y-chlorpropylbenzene and heating O-CH; the resulting chlorpropylphenol with a caustic alkali. It is a colourless oil which boils at 214-215° C. and possesses a characteristic peppermint odour. For the dibenzo-pyrones see XANTHONE.


PYROPE (pronounced pĭrōp), a deep red variety of garnet, named from the Gr. πυρωπός (fiery) in allusion to its colour. It is used, like almandine (q.v.), as a gem-stone, but may be distinguished by the absence of any tinge of violet in its colour and by its lower specific gravity (3.7 or 3.8, while that of almandine is 4.1 to 4.3). The typical colour of pyrope is blood-red, though sometimes a trace of orange gives rise to a hyacinthine hue: occasionally the mineral becomes nearly black, as seen in the pyrope of Arendal in Norway. Crystals are rare, but cubic forms have been observed. Pyrope may be regarded as a magnesium-aluminium garnet (see Garnet), but it usually contains more or less calcium, iron, manganese and chromium; and the rich colour of the mineral seems due to the presence of some of the last three metals, though their exact condition in the mineral has not been determined.

Pyrope generally occurs in grains embedded in peridotites (olivine rocks) or in serpentine resulting from their alteration, or it is found as loose grains in detritus due to the disintegration of the matrix. The grains may be surrounded by a chloritic rind, or by a crust of a fibrous mineral called by A. Schrauf kelyphite (from the Gr. κέλυφος, a nut-shell), which seems in some cases to be an amphibole. In the serpentine of Zöblitz and of Greifendorf near Leipzig, in Saxony, pyrope is characteristically developed; and the Saxon garnets, found loose in gravels, were referred to by G. Agricola as far back as 1546. Several localities in Bohemia are famous for yielding pyrope, and from its characteristic occurrence here it is often known, even when found elsewhere, as Bohemian garnet. The garnet-bearing district is a tract of about 70 square kilometres in the north of Bohemia, the chief locality being Meronitz near Bilin. It is notable that the pyrope is found at Meronitz in a clayey calcareous tufa or conglomerate, with opal and serpentine, products of the decomposition of a peridotite. It occurs also in sands and gravels near Chrastian, Lobositz, Triblitz, Podseditz, Chodolitz, and at several other localities in the Mittel Gebirge, between Teplitz and Leitmeritz. It is believed that the original pyrope-bearing rocks resulted from the eruptive activity which gave rise to Linhorka Hill, near Starrey. The garnets in the detritus are accompanied by zircon, spinel, corundum, cyanite, tourmaline, olivine, &c. Though generally very small, they are abundant, and are used not only as ornamental stones, but as a counterpoise in delicate weighing and as an abrasive agent. To obtain the stones the detritus is washed, and the garnets picked out by hand and then sized through sieves. The pyrope is generally rose-cut or step-cut, and often mounted with a foil. Beads are faceted all over. Some pyrope is cut en cabochon, forming, like almandine, carbuncle, and if very dark the stone is hollowed at the back so as to form a “ garnet shell." The industry of cutting Bohemian garnets is centred in Turnau on the Iser, near Reichenberg; but there are also works at other localities. Large stones are very rare, but a Bohemian pyrope as large as a hen's egg is preserved in the Imperial treasury at Vienna; and another the size of a pigeon's egg in the Grüne Gewölbe of Dresden.

Pyrope occurs in many localities in the western part of the United States, especially in Colorado, Arizona and New Mexico, where it is often called " ruby." it is found loose in sand accompanied by olivine, and has resulted from the alteration of a peridotite. The Navajo Indians of New Mexico collect the garnet from the sands of the ant-hills and scorpion-holes. Very fine pyrope occurs in the diamond-fields of South Africa, having been derived from olivine-bearing rocks. It occurs in the blue-ground and in the detritus of the river-diggings. The Cape garnets have usually a rich colour, but some stones incline to an orange hue. The finest pyrope is often cut as a brilliant, and passes under the misleading name of “ Cape ruby.” A pyrope-bearing rock, rather like that of South Africa, occurs in Elliott county, Kentucky, U.S.A.; it is notable, too, that pyrope is found near Elie in Fife, in Scotland, where it occurs in volcanic agglomerates and in basaltic dikes. Sir A. Geikie has pointed out the suggestive resemblance of the occurrence there to that in South Africa.

See “ Bohemian Garnets," by G. F. Kunz, Trans. Amer. Inst. Mining Eng. (1893), xxi. 241; and “ Die böhmischen Granatlagerstatten," by Dr Hans Oehmichen, Zeit. f. prakt. Geol. (1900), viii. 1. Both papers contain bibliographical lists. (F. W. R.*)


PYROPHORUS (Gr. πῦρ, fire, φέρειν, to bear), a substance which spontaneously inflames on contact with the air. One of the earliest known is that of Homberg, prepared by heating a mixture of alum and finely divided carbon to redness in a closed tube. On opening the tube and emptying out the black residue (consisting of potassium sulphide, aluminium sulphate and carbon) it promptly catches fire. Many readily oxidizable substances, especially when very finely divided, have the same property. Metallic iron and cobalt, when prepared under certain conditions, are pyrophoric, as is also ferrous oxide. Spontaneously inflammable liquids are also known, e.g. certain alkyl metallic compounds, phosphorus dihydride, &c.


PYROPHYLLITE, a mineral species belonging to the clay family, and composed of hydrous aluminium silicate HAl (SiO3)2. It occurs in two more or less distinct varieties, namely, as crystalline folia and as compact masses; distinct crystals are not known.

The folia have a pronounced pearly lustre, owing to the presence of a perfect cleavage parallel to their surfaces: they are flexible but not elastic, and are usually arranged radially in fan-like or spherical groups. This variety, when heated before the blowpipe, exfoliates and swells up to many times its original volume, hence the name pyrophyllite, from the Greek πῦρ (fire) and φύλλον (a leaf), given by R. Hermann in 1829. The colour of both varieties is white, pale green, greyish or yellowish; they are very soft (H. = 1–2) and are greasy to the touch. The specific gravity is 2.8–2.9. The two varieties are thus very similar respectively to talc (q.v.) and its compact variety steatite, which is, however, a hydrous magnesium