Page:The New International Encyclopædia 1st ed. v. 01.djvu/445

ALLOTROPY. ALLOT'ROPY (Eccl. Gk. nnrTimTrla, alio- trofiiu, variety, from aA?.of, a/Zos, other -)- rpoTrof, triijios. turn, way, guise), or Allotropism. A term used in chemistry to denote the exist- <'nce of an element in several forms difi'er- injf from eacli other in their pliysical proper- ties. By the silent discharge of electricity in an atmosphere containing ordinary oxygen, the latter is transformed into ozone. Ozone can be readily shown to be made up of nothing but the element oxygen : yet oxygen gas and ozone exhibit imjiortant differences in their properties; thus ozone (Gk. bCuv, smelling) has a peculiar and characteristic odor, while oxj'gen gas is odorless; ozone reacts much more readily with various substances; it has bleaching and disinfectant properties not pos- sessed by oxygen gas, and it is much denser than oxygen. Phosphorus affords another example of allotropism. In ordinary circumstances, and when freshlj' prepared, phosphorus is a pale yellow solid of the consistence and aspect of wax, and to some extent flexible and translucent. It requires to be placed in a vessel with water to keep it from taking fire spontaneously, and it is ver}' poisonous. The same element, when dried and kept for some time at a moderately high temperature, passes, weight for weight — without addition or subtraction of matter — into a substance known to chemists as amorphous phosphorus. The color of this new variety is brownish red; and it exists as a powder, which has no odor, does not take fire, and is not known to be poisonous at all. Three allotropic modifica- tions of the element carbon are known: diamond, graphite, and amorphous carbon (pure lamp- black). The different varieties of sulphur, boron, silicon, etc., furnish other examples of allotropism. Though comparatively few ele- ments have been obtained in more than one form, there seems to be no reason why, in general, any other chemical element should be incapable of existing in two or more allotropic modifications. The existence of allotropic varieties brings to the mind the polymorphism of crystalline substances and the isomerism of organic compounds. From the point of view of the atomic theory, the differ- ent allotropic modifications of an element are, probably, made up of molecules containing differ- ent numbers of atoms, or else of atoms differently combined: thus a molecule of ordinary oxygen contains two oxygen atoms, and its chemical symbol is 0,; a molecule of ozone contains three oxygen atoms, and its chemical symbol is 0.,. A similar explanation of the nature of allotropy in solid elements is, however, purely hj'pothetical ; for nothing at all is known of the ultimate structure of solids. Consult: D. Berthelot, De l'allotropie des corps simples (Paris, 1894); and Ouvrard, Etats allotropiques des corps simples (Paris, 1894). ALLOTTAVA. iil'lot-tU'va (It., at the oc- tave I. A mark (ill. Sro., or Sra., placed over the notes in pianoforte music, signifies that they are to be played an octave higher than written, or, if placed below the notes, an octave hjwer. Its duration is indicated by a dotted line. In orchestral scores, ull. Sva. signifies that one in- strument plays in octaves with another ; in figured bass, that no harmonies are to be em- ployed, the upper parts simply doubling the bass in octaves.

ALLOUEZ. a'looa', (1620-90). One of the early French Jesuits who visited the Great Lakes. He founded the Mission of the Holy Ghost on Lake Superior in 1665, explored Green Bay, and established missions among the Illinois Indians, settling at Kaskaskia (q.v.), and continuing there the mission begun by Marquette. He retired in 1679 on the approach of La Salle, an enemy of the Jesuits, and died among the Miamis on St. Joseph's River. An autobiographic account of his work can be found in the Jesuit Relations, published at Cleveland, O., in 1900.

ALLOWANCE. In military usage, money allowed in lieu of forage, food, horses, clothing, or quarters; or for any extra work or duties that may have been performed. Such allowance con- stitutes extra pay. See Pay and Allowances, Military.

ALLOWANCE OF QUAR'TERS. See Pay and Allowances, Military.

AL'LOWAY KIRK. An old ruined church in the parish of Ayr, Scotland, near the mouth of the Doon, celebrated in Burns's Tam o' Shanter. At very short distances from it are the cottage in which the poet was born, the monument erected to his memory in 1823, and the Auld Brig o' Doon, over which Tam o' Shanter made his escape.

ALLOY' (Fr. aloi, from Lat. alligare, to bind to, from ad, to + ligare, to tie). A mixture of two or more metals, usually produced artificially by fusion, although sometimes found native. Alloys are characterized by certain definite properties, which, according to Sir William C. Roberts-Austen, include: Liquation, which is shown by the separation of that constituent which has the lowest melting point when the alloy is heated; density, which seldom corresponds to the mean of those of the constituents of the alloy, being usually either more or less than that shown by the percentage composition; tenacity, which is usually greater than that of the constituents of the alloy, although it is sometimes diminished; hardness, which is almost always increased; extensibility, which is almost always diminished; and fusibility, the melting point being generally lower than the mean of the melting points of the constituent metals. Matthiessen, who studied the subject of alloys very thoroughly, divided the constituents of alloys into two classes: Those metals which impart to their alloys their physical properties in the proportion in which they themselves exist in the alloy, and those which do not impart to their alloys their physical properties in the proportion in which they themselves exist in the alloy. In the first class he places lead, tin, zinc, and cadmium, and in the second class, in all probability, the rest of the metals. He divided the physical properties of alloys into three classes: (1) Those which in all cases are imparted to the alloy approximately in the ratio in which they are possessed by the component metals; (2) those which in all cases are not imparted to the alloy in the ratio in which they are possessed by the component metals; (3) those which in some cases are, and in others are not, imparted to the alloy in the ratio in which they are possessed by the component metals. As types of the first class, specific gravity, specific heat, and expansion due to heat, may be taken; as types of the second class, the fusing points and crystalline form; and as types of the third class, the con-