A L L A L L 587 tions, as well as the county court-house, a corn exchange, and schools of various grades. In the immediate vicinity of the town is an ancient tower, 89 feet high, with walls 1 1 feet in thickness, said to have been built about the year 1315, formerly the residence of the powerful family of Erskinc, descendants of the Earls of Mar. Here many of the Scottish princes received their education as wards of the Lords Erskine and the Earls of Mar, the last of these educated here being Henry, the eldest son of James VI. Among the manufactures of Alloa are ale, whisky, iron goods, glass (especially bottles), bricks, yarns, shawls, and blankets. Shipbuilding is also carried on to some extent, and in the neighbourhood there are several collieries. The harbour is safe and commodious, having a depth of 16 feet at neap, and 22 at spring tides; adjoining it is an excellent dry dock, and a capacious wet dock was con structed in 18G3. In 1872, 446 vessels of 49,941 tons entered, and 533 of 70,499 cleared the port of Alloa, in addition to coasting vessels in ballast; and in the same year 453 were derived from customs duties. The chief exports were pig-iron, ale, glass, and coals; the imports, timber, grain, iron, linseed, and flax. There is a ferry here across the Forth. Population in 1871, 9362. ALLODIUM or ALODIUM denotes lands which are the absolute property of their owner, and not subject to any service or acknowledgement to a superior. It is thus the opposite of fe-odum or fief. The proper derivation of the word has been much discussed and is still doubtful, though it is probably compounded of all, whole or entire, and odk, property. Allodial tenure seems to have been common throughout northern Europe. It exists in Orkney and Shetland, where the proprietor of an allodial estate was known until recently as an udaller. (See Sir Walter Scott s Pirate.) In England allodial tenure is unknown, the feudal system having been made universal by William the Conqueror. ALLORI, ALESSANDRO, a painter of the Florentine school, was born at Florence in 1535, and died in 1607. Having lost his father in his fifth year, he was brought up and trained in art by his uncle, Angelo Bronzino, whose name he sometimes assumed in his pictures. Visiting Home in his nineteenth year, he carefully studied the works of Michael Angelo; but having himself little genius and no originality, the influence of that great master can only be traced in the anatomical correctness of his draw ing of nude figures. He was very successful as a portrait- painter. ALLORI, CRISTOFANO, son of the preceding, was born at Florence on the 17th October 1577, and died in 1621. He received his first lessons in painting from his father, but becoming dissatisfied with the hard anatomical drawing and cold colouring of the latter, he entered the studio of Pagani, who was one of the leaders of that later Florentine school which endeavoured to unite the rich colouring of the Venetians with the correct drawing; of Michael Angelo s o o disciples. Allori became one of the foremost of this school. His pictures are distinguished by their close adherence to nature and the delicacy and technical perfection of their execution. His technical skill is proved by the fact that several copies he made after Correggio have been taken to be duplicates by Correggio himself. His extreme fastidiousness limited his power of production, though the number of his works is not su small as is sometimes asserted. Several specimens are to be seen at Florence and elsewhere. The finest of all his works is his " Judith and Holofernes," in the Pitti palace. The model for the Judith was his mistress, the beautiful Mazxafirra, who is also represented in his Magdalene ; and the head of Holo fernes is generally supposed to represent himself, though this is questioned by the best authorities. ALLOTROPY (from aXXos, other, and T/JOTTOS, manner), a name applied to a property, whereby certain substances, chemically simple, assume different forms and conditions without undergoing chemical change. Sulphur and phos phorus, for instance, occur sometimes in crystals and sometimes in an amorphous state, being in the latter case sometimes translucent and sometimes opaque, and present very different properties under these different conditions. Ozone is an allotropic form of oxygen. The name isomerism is given to the similar by no means uncommon property whereby compound bodies, although entirely distinct, are made up of the same chemical elements in precisely the same proportions. ALLOXAN, a product of the action of oxidising agents on uric acid, obtained by adding slowly, in small quantities, uric acid to strong nitric acid of specific gravity 1 4, kept cool, and stirring constantly. Carbonic acid and nitrogen are evolved during the action, and the alloxan crystallises out on standing. It is purified by recrystallisation from water, and then has the composition C 4 H !! N. i O 4 + aq. Tho crystals of this compound are large and colourless, and when heated to a temperature of 150 C., lose the water of crystallisation, and acquire a red colour. Alloxan is readily soluble in water and alcohol, and its aqueous solution reddeus litmus, has an astringent taste, and colours the skin purple after some time. It produces a great number of derivatives, for which see URIC ACID. ALLOY, the name given to a combination obtained by fusing metals with each other. Few metals are employed in the pure state, with the exception of iron, copper, lead, tin, zinc, platinum, aluminium; metals are more frequently used in the forms of alloys for technical purposes. Every indus trial application necessitates special qualities that may not occur in any isolated metal, but which may be produced by the proper mixture of two or more of these substances. Thus gold and silver, which in their pure state are too soft and flexible for the manufacture of plate, coin, trinkets, <tc., are hardened by the addition of a tenth part of copper, while the colour and other valuable qualities are not mate rially impaired. Similarly copper is rendered hard by mixture with zinc, when we obtain brass, an alloy of a beautiful yellow colour, easier to work than the pure metal. If brass has to be used in turning operations it is found to tear under the action of the chisel, unless a small quantity of lead has been added. These examples arc sufficient to show that an alloy is really an industrial metal, often of greater importance than the metals which compose it. Alloys are equally interesting from a purely scientific point of view. They are not only mixtures of metals having certain particular qualities, but in reality arc true chemical compounds, generally dissolved in an excess of one of the constituent metals. In the appearances which accompany the union of the metals, and in the properties of the resulting products, we observe that which charac terises the manifestation of affinity, that is, an evolution of heat and light, resulting in the formation of substances having a definite composition, distinct crystalline form, and a variety of properties different from those of the constituents. If a piece of clean sodium is rubbed in a mortar with a quantity of dry mercury, the metal dissolves, producing a harsh sound resembling the immersion of red hot iron in water. This phenomenon is due to the large evolution of heat which accompanies the combination, as the mercury rises rapidly in temperature on the addition of each succes sive piece of sodium. If the mass is allowed to cool after the action, long needles of a white brilliant alloy of definite composition crystallise from the middle of the liquid, from which the excess of mercury may be separated by decanta- tion. Platinum, iridium, gold, rhodium, ruthenium, and
silver unite with tin, producing an evolution of heat ; if
