Ar´ru (or Aroo) Islands, a group belonging to the Dutch, south of western New Guinea, and extending from north to south about 127 miles. They are composed of coralline limestone, nowhere exceeding 200 feet above the sea, and are well wooded and tolerably fertile. The natives belong to the Papuan race, and some of them are Christians. The chief exports are trepang, tortoise-shell, pearls, mother-of-pearl, and edible birds'-nests. Pop. of group about 20,000.
Arsa´ces, the founder of a dynasty of Parthian kings (256 B.C.), who, taking their name from him, are called Arsacidæ. There were thirty-one in all. See Parthia.
Ar´samas, a manufacturing town in the Russian government of Nijni-Novgorod, on the Tesha, 250 miles east of Moscow, with a cathedral and large convent. Pop. 12,000.
Ar´senal, a royal or public magazine or place appointed for the making, repairing, keeping, and issuing of military stores. An arsenal of the first class should include factories for guns and gun-carriages, small-arms, small-arms ammunition, harness, saddlery, tents, and powder; a laboratory and large store-houses. In arsenals of the second class workshops take the place of the factories. The Royal Arsenal, Woolwich, which manufactures warlike implements and stores for the army and navy, was formed about 1720, and comprises factories, laboratories, &c., for the manufacture and final fitting up of almost every kind of arms and ammunition. Great quantities of military and naval stores are kept at the dockyards of Chatham, Portsmouth, Plymouth, and Pembroke. In France there are various arsenals or depots of war-material, which is manufactured at Mézières, Toulouse, Besançon, &c.; the great naval arsenals are Brest and Toulon. Until 1919 the chief German arsenals were at Spandau, Strassburg, and Dantzig. The chief Austrian arsenal was the immense establishment at Vienna, which included gun-factory, laboratory, small-arms and carriage factories, &c. Russia had her principal arsenal at Petrograd, with supplementary factories of arms and ammunition at Briansk, Kiev, and elsewhere. In Italy Turin is the centre of the military factories. There are a number of arsenals in the United States, but individually they are of little importance.
Ar´senic (symbol As, atomic weight 75), a common element usually found combined with metals as arsenides, the commonest of which is arsenical pyrites, FeAsS. It has a steel colour and high metallic lustre, and tarnishes on exposure to the air, first changing to yellow, and finally to black. In hardness it equals copper; it is extremely brittle, and very volatile, beginning to sublime before it melts. It burns with a blue flame, and emits a smell of garlic. Its specific gravity is 5.76. It forms compounds with most of the metals. Combined with sulphur it forms orpiment and realgar, which are the yellow and red sulphides of arsenic. Orpiment is the true arsenicum of the ancients. With oxygen arsenic forms two compounds, the more important of which is arsenious oxides or arsenic trioxide (As4O6), which is the white arsenic, or simply arsenic of the shops. It is usually seen in white, glassy, translucent masses, and is obtained by sublimation from several ores containing arsenic in combination with metals, particularly from arsenical pyrites. Of all substances arsenic is that which has most frequently occasioned death by poisoning, both by accident and design. The best remedies against the effects of arsenic on the stomach are ferric hydroxide or magnesic hydroxide, or a mixture of both, with copious draughts of bland liquids of a mucilaginous consistence, which serve to procure its complete ejection from the stomach. Oils and fats generally, milk, albumen, wheat-flour, oatmeal, sugar or syrup, have all proved useful in counteracting its effect. Like many other virulent poisons it is a safe and useful medicine, especially in skin diseases, when judiciously employed. It is used as a flux for glass, and also for forming pigments. The arsenite of copper (Scheele's green) and a double arsenite and acetate of copper (emerald green) were formerly largely used to colour paper-hangings for rooms; but as poisonous gases are liable to be given off, the practice has been to a great extent abandoned. Arsenic compounds have been used for colouring confectionery, and other articles, bright green, but their chief industrial use is in the preparation of insecticides. Arsenic is found in crude oil of vitriol, and occasionally in products such as grape-sugar, beer, &c., in the manufacture of which oil of vitriol is employed. Plants die when placed in a solution of arsenic, but corn is often steeped in such a solution, previous to planting, for preventing smut, and the growth of the future plant is not injured thereby.
Arshin (a˙r-shēn´), a Russian measure of length equal to 28 inches.
Arsin´oë, a city of ancient Egypt on Lake Mœris, said to have been founded about 2300 B. C., but renamed after Arsinoë, wife and sister of Ptolemy II of Egypt, and called also Crocodilopolis, from the sacred crocodiles kept at it.
Ar´sis, a term applied in prosody to that syllable in a measure where the emphasis is put; in elocution, the elevation of the voice, in distinction from thesis, or its depression. Arsis and thesis, in music, are the strong position and weak position of the bar, indicated by the down-beat and up-beat in marking time.
Ar´son, in English law, the malicious burning of a dwelling-house or outhouse of another man, which by the common law is felony, and which, if