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ACHARD aioi. Their 12 little towns formed a confederacy, renewed in 281 B. C, and subsequently extended, under the name of the Achæan League, throughout Greece, until 146 B. C, when Greece fell under the power of Rome. Pop. 225,000.

ACHARD, LOUIS AMÉDÉE (ä-shär´), a French novelist and publicist, born in 1814. Originally a merchant, he became a contributor to several papers in Paris in 1838. After the revolution of 1848 he was for a time active as a political writer in support of the royalist cause. He depicts pre-eminently conflicts in family life and society. He died in 1875.

ACHATES, a friend of Æneas, whose fidelity was so exemplary that fidus Achates (the faithful Achates) became a proverb.

ACHERON, the river of sorrow, which flowed round the infernal realms of Hades, according to the mythology of the ancients.

ACHESON, EDWARD GOODRICH, an American inventor, born in Washington, Pa., in 1856. He received an academic education and for a short time acted as assistant of Thomas A. Edison. He invented carborundum, silicon, and several methods of making graphite. He has received medals from many American and foreign scientific societies, and has been president of the American Chemical Society and an officer and member of many other chemical societies.

ACHILLES (ak-il´ēz), son of Peleus, king of the Myrmidons, in Thessaly, and of Thetis, daughter of Nereus. He joined the Grecian army, in which he was pre-eminent in valor, strength, swiftness, and beauty. Before Troy a quarrel broke out between him and the general-in-chief, Agamemnon, which led him to withdraw entirely from the contest. In consequence, the Trojans reduced the Greeks to extreme distress. The Greek council of war now sent its most influential members to soothe the anger of Achilles, and to induce him to return to arms, but without effect. Rage and grief, caused by the death of his friend Patroclus, slain by Hector, induced Achilles to return to battle. At the close of a day of slaughter he killed Hector, and dragged him at his chariot wheels to the camp. Here ends the history of Achilles, so far as it is derived from Homer. By later authors, a variety of fable is mixed up with this simple narrative. Thetis is said to have dipped him, while an infant, in the Styx, which rendered him invulnerable except in the heel by which she held him, and he was killed at last by a wound in the heel.

ACHILLES TENDON, a tendon, so called because, as fable reports, Thetis, the mother of Achilles, held him by that part when she dipped him in the river Styx to make him invulnerable. It is the strong and powerful tendon of the heel, which is formed by the junction of divers muscles, and which extends from the calf to the heel. When this tendon is cut or ruptured, the use of the leg is immediately lost; and, unless the parts be afterward successfully united, the patient will remain a cripple for life.

ACHMET TEWFIK PASHA, a Turkish statesman, born in 1818 at Constantinople. His father was a Greek convert; his mother was a Jewess. He was educated at Paris. He was appointed commander for the Porte, and displayed great diplomatic talent, and was sent, in 1851, as Ambassador to Persia. On his return he became a member of the state council and of the military council. He was regarded as one of the leaders in the Turkish reform party. In 1860 and 1861 he was Ambassador to Paris. He translated Molière into Turkish, and wrote a geographical text-book for schools. In 1877 the Sultan appointed him President of the first Turkish Chamber of Deputies. In 1878 he was Premier and signed the Peace of Santo Stefano. He died in June, 1891.

ACHROMATIC. See TELESCOPE.

ACI (ä´chē), or ACI REALE, a seaport town in Sicily, province of Catania, well built with lava, having a castle and many fine edifices. It has manufactories of silks, linens, cutlery, and filigree work. Pop. about 37,000.

ACIDS, in chemistry, a salt of hydrogen in which the hydrogen can be replaced by a metal, or can, with a basic metallic oxide, form a salt of that metal and water. Acid oxides of the same element are distinguished by the termination of -ous and -ic—as sulphurous and sulphuric—the latter containing the most oxygen; they are also called anhydrides. They unite with water and form acids having the same terminations. By replacement of the hydrogen by a metal they form salts distinguished by the terminations -ite and -ate respectively. These acids are called oxygen acids. Many acids are formed by direct union of hydrogen with an element, as hydrochloric acid (HCl), hydrosulphuric acid (H2S), or with an organic radical, as hydrocyanic acid, H(CN). Acids which are soluble in water redden blue litmus, and have a sour taste. Organic acids can be produced by the oxidation of an alcohol or aldehyde. They contain the monad