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260 ALCAMO ALCHEMY ALCAMO, a city of Sicily, in the province of Trapani, 23 m. S. W. of Palermo ; pop. in 1872, 20,890. It was originally a Saracenic town, built on the summit of a neighboring hill. The Saracens were expelled in 1223, and the town was rebuilt at the foot of the hill. It is sur- rounded by a battlemented wall of the 14th century, but the place is very poor and decayed. In the vicinity are the ruins of ancient Segesta and quarries of yellow marble. AIA AVTAKA (Arab., the bridge ; anc. Norba Casarea). I. A small town in Spanish Estre- madura, near the Portuguese frontier, on the left bank of the Tagus, in the province and 34 m. W. N. W. of Caceres; pop. about 4,500. A magnificent six-arch bridge, built across the Tagus hi the reign of Trajan, was blown up by the British during the Peninsular war. II. Knights of, a Spanish order deriving their origin from the knights of San Julian de Peyrero, a small body of valiant Christians in the 12th century who vowed continual war against the Moors. In 1215 Alcantara, which had been in possession of the Moors, was recovered by Al- fonso IX., and the grand master of Calatrava being unable to undertake its defence, the duty was assigned to the brothers of San Julian, who changed their name to that of knights of Alcantara. In 1495, the grand master dying, Ferdinand the Catholic became administrator of the order, and united the office of grand master with the crown. The order as an or- ganized body has since been abolished, and exists now only as a military order of merit. In addition to the usual vows of the monk- soldier, the knight of Alcantara was bound to maintain the immaculate conception of the Vir- gin. After 1540 a change was made in the statutes of the order, which permitted the knights to marry. ALCAYALA, or Alrabala, a duty imposed in Spain and its colonies on all transfers of prop- erty. It was originally laid in 1341 as an ad valorem tax of 10 per cent., and was afterward increased to 14 per cent. It was even levied on such movable chattels as manufactured com- modities, and was attached to all wholesale transactions. This oppressive impediment to the operations of trade continued over the greater part of the Spanish realm until swept away by Napoleon in 1808. Catalonia and Aragon purchased from Philip V. an exemp- tion from the alcavala by the substitution of a tax on rents and on incomes. ALCAZAR (Arab., the royal castle). I. In Spanish, the general name for a castle or citadel applied to the castles at Seville and Segovia, and to many others. II. Alcazar de San Juan, a town of Spain, in New Castile, in the province and 48 in. N. E. of Ciudad Real ; pop. about 8,000. It has manufactures of salt- petre, soap, chocolate, &c., and is also a rail- way centre, where the line from Valencia joins that from Madrid to C6rdova. Near it are rich iron pits. ALCESTIS. See ADMETUS. ALCHEMY (Arab, al-kimia, from al, the, and Gr. xw i a i chemistry), the ancient name for the science of chemistry. It is sometimes called the hermetic art, from Hermes Trismegistus, anciently reputed its discoverer. The word alchemy is first found in the works of the Greek author Zosimus of Pannopolis, Avho wrote in the early part of the 5th century. During the middle ages it was a mysterious art, aiming to change inferior metals into sil- ver and gold, and to find the so-called elixir of life, which was to be the universal remedy for all possible diseases, rejuvenating the old, and even preventing death. From the 10th to the 17th century there was no .distinction made between the words chymia or chemistry and alchemy ; but since the latter period, this class of researches becoming more positive and scien- tific, it has been agreed to confine the use of the word chemistry to the positive modern knowledge, and to designate by the term al- chemy that imaginary science which sought impossible results from misunderstood or mis- applied principles. For this reason the name alchemist has become an expression of contempt. Still the ancient alchemists, who called the sub- ject of their investigation the divine art, were the precursors of our modern science, and en- riched posterity with the knowledge of many valuable facts, which laid the foundation of chemistry. The first authentic account of alchemy is found in Suidas, a Byzantine author of the 10th or llth century, who mentions that the emperor Diocletian, after the conquest of the rebellious Egyptians in the year 296, ordered that all the writings on the chemistry of gold and silver should be burned, in order that the people should not grow too rich by making gold and again commence a rebellion. It appears further that the Greeks living in Egypt in the 5th century were industrious laborers in this field, as a great number of gen- uine manuscripts on alchemy, dating from the 5th and 6th centuries, are now found in many of the large libraries in Europe, nearly all coming from Alexandria. The Arabs learned this art, after their great invasion of northern Africa and southern Europe, from some of the peoples they conquered. The greatest Arabian author on alchemy, Jaffar or Geber, who lived toward the end of the 8th century in Seville, was enlightened enough not to suppose that any alchemist had ever succeeded in making gold. However, it appears that he did not doubt the possibility of the transmutation of metals, as he believed that all metals were compounds of three elements. With all their errors, however, some of the ancient Arabian authors give very striking definitions of alchemy, such as the science of the balance, the science of weight, the science of combustion. Jaffar, or Geber, marked an epoch in chemical science equal to that of Lavoisier exactly 1,000 years later. In his tune no stronger acid was known than concentrated vinegar, and he discovered and described nitric acid and aqua regia, and also