PURPLE OF CASSIUS PUKSLANE 95 ties of the lichen called orchilla weed. Oth- er lichens growing in different parts of the world now furnish the dye known as orchil or archil. (See AECHIL.) Shades of purple are abundantly obtained from coal-tar colors. (See ANILINE, DYEING, and MAUVE.) The compounds called "purpurates," especially the purpurate of ammonia, called by Liebig and Wohler murexide, from its resemblance to the Tyrian purple, present beautiful shades of pur- ple. (See PuRPtTEATES.) PURPLE OF CASSIUS. See CASSIUS, PURPLE OF. PURPURATES, salts of purpuric acid. Scheele in 1776 found that a solution of uric in nitric acid produced a beautiful deep red dye. Prout in 1818 obtained this coloring matter in a crystalline form, and regarded it as purpurate of ammonia. By double decomposition he obtained metallic purpurates having a similar color. The colorless substance which sepa- rated from purpurate of ammonia by the ac- tion of strong acids, he regarded as purpuric acid; but Liebig and Wohler showed that this did not possess the property of forming colored salts, and therefore held that Prout's com- pound was not an ammonium salt, but an amide, ' which they called murexide. (See MUREX.) Later researches by Freitzsch and Beilstein in- dicate that it is a true ammonium salt ; still the purpuric acid has never been isolated, be- cause it is decomposed when its salts are treat- ed with a stronger acid. The formula of pur- purate of ammonia or murexide is OsHsNeOe^ KH^Cs^NsOe ; therefore the acid is repre- sented by the formula CsEUNsOe. Murexide is the principal salt, and is a beautiful purple, but is becoming superseded by rosaniline. PURSH, Frederick, an American botanist, born in Tobolsk, Siberia, in 1774, died in Montreal, Canada, June 11, 1820. He was educated at Dresden, came to America in 1799, and spent 12 years in botanical explorations. In 1811 he visited England, and published " Flora Americas Septentrionalis, or a Systematic Ar- rangement and Description of the Plants of North America" (2 vols. 8vo, London, 1814). He was engaged in the collection of materials for a flora of Canada when he died. PURSLANE, the common name (of obscure derivation) for portulaca oleracea, one of the most common weeds of our gardens, and often abbreviated to " pusley." Portulaca (the an- cient Latin name) gives its name to a small family of succulent annual or perennial herbs, the portulacacece, closely related to the pink family, from which they are mainly dis- tinguished by their two-sepalled calyx, and the often transversely dehiscent capsule, which opens by the falling away of the upper part as a lid. The common purslane is a prostrate, smooth, annual plant, its fleshy and often red- dish stems spreading in all directions, and forming a mat a foot or more across ; the alternate or opposite leaves are wedge-shaped or obovate, and half an inch to an inch long ; the axillary or terminal flowers sessile; the 691 VOL. xiv. 7 two-cleft calyx cohering with the ovary below ; petals five, yellow, and with the 7 to 12 sta- mens inserted on the calyx at the point where it becomes free from the ovary ; ovary one- celled, with a deeply five- to six-parted style, ripening to a many-seeded capsule, which opens by a lid ; the kidney-shaped seeds are shining and handsomely marked with a net- work. The flowers open only in bright sun- shine, usually about 11 o'clock A. M., and re- main but a short time. Purslane has been used as a pot herb from very ancient times, a fact recognized in its specific name, oleracea ; and though it is but little used in this country, it is cultivated in French gardens as pourpier, and seeds of the green, golden, and large golden varieties are offered in their catalogues. When grown rapidly in a rich soil, and properly served, it is to many a most acceptable vege- table. In this country it finds a congenial climate, and is everywhere one of the most Common Purslane (Portulaca oleracea). prominent weeds ; it gives but little trouble before hot weather sets in, but grows then with astonishing rapidity ; so tenacious of life is it, that it must be entirely removed from the ground or it will go on and perfect its seeds. Pigs are very fond of it. The hairy purslane, P. pilosa, with narrow cylindrical leaves and pink or purple flowers, is found in Florida; and P. retusa, which much resembles the common species, with its leaves notched at the ends, is common west of the Mississippi. The garden portulacas, probably all to be re- ferred to the South American P. grandiflora, though several different names have been given to them, have cylindrical leaves and very large showy flowers of the most brilliant colors, from white through yellow, orange, and red, to bright purple, and often striped or blotched with two colors ; the double ones are very fine, and deserve the name of "portulaca roses " given them by the German florists.
