Page:The New International Encyclopædia 1st ed. v. 17.djvu/842

* SEL D'OK. 764 in fixing the image on n .lni;ncncot.viH' plate. At present it is used in toninj; positive prints. It is formed by gradually adiling a neutral 2 per cent, sohition of gold chloride to a solution con- taining three times as much sodium tliiosulphate. After each addition it is necessary to wait until the red liquid which is formed loses its color, nfter which the salt is precipitated with strong alcohol, and then allowed to crystallize. SELENE. sMe'nf (I.at.. from Gk. ScX^kt;, connected with (riXas. Kchis, brightness, SUt. .sior, Av. Inti^, sun). The tJreek name of the moon and its goddess, called also MrivTi, Mcnv, and in Latin Luna. Her myth is difl'ercntly told, but the most common account makes her a daughter of Hyperion and Tluia. and sister of Helios (the sun) and Eos (the dawn). She was represented as riding in a chariot drawn by a span of horses, winged, and shedding soft light from her golden crown, or else riding on a horse or mule. Legend said that by Zeus she became mother of Pandia, 'the all-shining,' and that Pan had also won her love. Most famous was her passion for Endyniion, who, according to the Carian legend, lay sunk in eternal sleep in a cave on Slount Latmos, where he was nightly visited by Selene. In Elis, however, the story told how she bore to Endyniion, son of the King, fifty daughters. The sliar'plv lrans])arenl cliaractcr of tlu> name seems to have kept Sclcnc from developing into so dis- tinct a personality as other early moon-goddesses. When Apollo became so strongly identified with the .sun, it was natural that Artemis should be restored to her position as a moon-goddess, and in later literature and art we find the crescent an attribute of Artemis or Diana. Consult Koscher, Veher Helene iind ]'rrir(iii<itcs (Leipzig, 1890), and Xachtniige (Leipzig, 1S95). SELEN'GA. A river of Northern Asia, rising in tlie Khangai Mountains of Mongolia. It Hows for a considerable part of its course in a northeastern direction, and after turning to the north, passes into the Siberian territory of Trans- baikalia, and enters Lake Baikal through a wide delta (Map: China, B 2). Its total length is over 700 miles, and, although its swift current in- terferes to some extent with navigation, it is an important factor in the commercial intercourse between Mongolia and Siberia, flowing through the most settled part of Transliaikalia and touch- ing the Trans-Siberian Railway. Its fisheries, which are exploited on a consiclerable scale, also add to the economic importance. SELENITE (Lat. selenites^ seleiiifis, from Gk. o-cXtji/i'tt)!, relating to the moon, from o-eXiji'T), seleni, moon). The variety of calcium sulphate, or gypsiun, that is crystallized in the mono- clinic system. It is usually white or tinged with light shades of green, gray, or yellow. Fine speci- mens are found at Bex, Switzerland; in Sicily; in England : also in Nova Scotia, and in the United States at various localities, in New York, Maryland, Ohio, and Kentucky. It sometimes occurs in broad transparent sheets as much as one yard across. In this condition the mineral is capable of being split into extremely thin plates that are flexible and were used by the ancients in place of glass. SELENIUM (Neo-Lat., from Gk. ati,vTi, seline, moon). A chemical element discovered in 1817 by Berzelius, who obtained it from crys- tals formed in the lead chambers of sulphuric SELEUCIA. acid works. Tlie element is somewhat widely distributed, though in small quantities. It occurs chiefiy in combination with copper, lead, and sil- ver, as in clausthalitc (lead sulphide), lehrbach- ite (lead and mercury sulphide), onofrite (mer- cury sclenide and sulphide), crookesite (copper, thallium, and silver sclenide) ; also in smaller quantities in other minerals, especially in certain pyrites and ehalcopyrites. It is obtained chielly from the flue dust formed in roasting sulphides containing selenium, or from the deposits in the lead chambers of sulphuric acid works. These deposits are mixed with equal parts of sulphuric acid and water to a tliin paste, and then boiled, with the addition, from time to time, of a little nitric acid, or potassium chlorate, until the red color disappears and the solution of selenic acid thus obtained is heated with fuming hydrochloric acid, yielding selenious acid, the cold solution of which, when saturated with sulphur dioxide, fur- nishes a red pulverulent precipitate of selenium. Selenium (symbol Se; atomic weight, 79.17) exists in several allotropic forms, of which the red or amorphous variety, which is soluble in carbon disulphide, has a specific gravity of 4.3, and has no definite melting-point, but softens gradually on heating. When the soluble sele- nium is slowly heated from 100° C. to 217° C, it passes into a black, glossy, metallic crystalline mass, which has a specific gravity of 4.8, is in- soluble in carbon disulphide, and melts at 217° C. Selenium is both odorless and tasteless, but it burns with a redclish-hlue flame that has a pecu- liar odor resembling liorseradish. The crystal- line variety of the element conducts electricity, its resistance increasing when heated, but dimin- ishing considerably on exposure to light, especial- ly red rays. The change of conductivity is in- stantaneous, and is almost doubled in sunlight, though even the light from a small lamp has a perceptible influence. It was upon this property that the construction of the photoplione (q.v.) was based. With oxygen selenium forms a di- oxide, which combines with water to form sele- nious acid. A selenic acid is produced by the ac- tion of chlorine on aqueous selenious acid. Sele- nious and selenic acids form salts, termed, respec- tively, selenites and selenates. SELENKA, zu-len'ka, Emil (1842-1902). A German zoiilogist, born in Brunswick, and edu- cated there at the Collegium Carolinum and at the University of Giittingen, xmder Keferstein. In 1868 he was made professor of zoiilogy and comparative anatomy at Leyden, and in 1884 he accepted a chair in Erlangen. His works dealt chiefly with comparative anatomy and embryology of the vertebrates, Zoologische Stiidien. (1878- 81), Entirickelunfisfiesf-hichte der Tiere (1883- 2}, Zooloqisches 'Taschpttbuch{3A ed., 1885), and Menschennffen (1898-1902) being the chief titles. SELEUCIA, se-lu'shi-a (Lat., from Gk. 2eei)K«a, Selevkeia) . The name of a number of ancient cities of Asia, situated in Syria, Pisidia, Pamphylia, Cilicia, Caria, and Mesopotamia, founded during the earlier existence of the dy- nasty of the Seleucidac (q.v.). The most noted of these were: (1) Seleucia PiEEiA (near the mod- ern Suadeiah ) . founded by Seleucus Nicator at the foot of Moimt Pieria, on the seashore, about 4 miles north of the mouth of the Orontes, and strongly fortified. It was the seaport of Antioch, and became of great importance during the ^vars between the Seleucidse and the Ptolemies for the