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LEFT SILCHESTER 429 SILISTRIA repeated interviews with the rajah and his minister. The capital is at Tumlung from November to May; for the rest of the year it is removed to Chumbi, on the Tibetan side of the range. The products are rice, Indian corn, millet, oranges, tea, and cotton cloth; the minerals are lime and copper. Pop. about 88,000. SILCHESTER, a village in the ex- treme N. of Hampshire, England; 7 miles N. of Basingstoke; is famous for the re- mains of the ancient Romano-British town of Caer Segeint, called by the Ro- mans Calleva, and by the West Saxons Silceastre. The chief visible remains are the amphitheater, 50 yards by 40, and the walls, 2,760 yards in length; excavations have shown the foundations of a basilica, the forum, a temple, baths, etc.; and coins, seals, rings, and much broken pot- tery have been found. New excavations were begun in June, 1890, by the Society of Antiquaries and by 1910 most of the old town was uncovered. SILESIA (German, Schlesien), a ter- ritory of Central Europe, formerly di- vided politically between Prussia and Austria. Prussian Silesia, the largest of the Prussian provinces, was bounded E. by Posen and Poland, S. by the Austrian territories, W. and N. by Saxony and Brandenburg; area, 15,566 square miles. The province is intersected by branches of the Sudetic mountains in the S., but is level toward Brandenburg and Posen, and though in parts marshy and sandy is yet fertile. The principal river is the Oder. Silesia produces corn, beet-root, flax, madder, hemp, hops, tobacco, fruits, and tolerable wines. The mountainous parts yield timber and afford good pas- turage and meadow land. Minerals in- clude iron, copper, lead, silver, coal, sul- phur, etc., and there are mineral waters in several places. Linen, lace, cotton, and woolen goods, and leather, glass, earthen- ware and iron ware are the chief manu- factures. Silesia was divided into three governments — Breslau, Liegnitz, and Op- peln. Breslau is the capital. By a pleb- iscite held in March, 1921, a majority of the people of Upper Silesia elected to remain German, rather than join Poland. Silesia was annexed to Poland in the beginning of the 10th century. In 1163 it became independent, and was governed by three dukes of the royal house of Piast. At the beginning of the 14th century 17 independent dukes reigned in Silesia at one time, and ruined the country by their feuds. In order to escape the grasp of Poland it acknowledged the sovereignty of the Bohemian kings. In 1675 the ducal line of Piast became extinct, and the country was incorporated in the Austrian dominions. In 1740 Frederick II. of Prus- sia laid claim to part of Silesia (based on old agreements to which effect had never been given), and in 1763, at the close of the Seven Years' War, a great part of Silesia was ceded to Prussia. Pop. about 5,225,900. By the Peace Treaty of 1919, Czecho-Slovakia obtained 1,996 square miles of Prussian and Austrian Silesia with a population of 608,128. On October 20, 1921, the Council of the League of Nations denned the Upper Si- lesian boundary. Germany retained the north and west, but Poland, in the coun- try around Kattowitz and Rybnick, got an important part of the mining district. SILICA, oxide of silicon. Pure silica occurs in nature, crystallized in six-side J prisms, terminated by six-sided pyramids in rock crystal and some other forms o£ quartz. It enters largely into the compo- sition of agate, chalcedony, flint, opal, sandstone, felspar, and a vast number of other minerals. In a perfectly pure state it is quite transparent and colorless. Its hardness is next to that of the precious stones, and it has a sp. gr. of 2.6. Silica presents the general characters of an earthy base, but acts as an acid, forming with the bases compounds known as sili- cates. These are very abundant in na- ture; clay, felspar, mica, hornblende, and a large number of other common minerals are compounds of this description. SILICON, in chemistry, one of the non-metallic elements, the base of silica, discovered by Berzelius in 1823. It is in the form of its only oxide, silica, the most abundant^ solid element in nature. It is obtained in a state of purity by igniting the double fluoride of silicon and potas- sium with sufficient potassium to combine with the whole of the fluorine. The mass is washed first with cold, and then with hot water. Silicon thus obtained is a dull-brown powder, sinking in water, in which it is insoluble. It is a non-conduc- tor of electricity, and is insoluble in all acids but the hydrofluoric. Heated in oxygen or air, it burns with a brilliant flame, being converted into silica, its only oxide. If heated in a closed platinum crucible its properties become changed. It is now insoluble in hydrofluoric acid, it is decreased in bulk, and may be heated strongly in air and oxygen without taking fire. Silicon unites with hydrogen, form- ing a gas spontaneously inflammable in air or oxygen. Equiv., 28; symbol, Si. SILISTRIA, a town of Rumania (for- merly belonging to Bulgaria), on the right bank of the Danube, 66 miles N. E. of Shumbla. For five centuries it was the main defensive point of the Turkish em- pire on the N. E. It was an ill-built and dirty town till the Crimean War, but BB— Cyc Vol 8