Page:Collier's New Encyclopedia v. 01.djvu/164

ALLOPATHY a superior. In most European countries where feudal tenure arose, it grew up by individual surrender of allodial tenure; consequently allodial tenure continued in some measure to exist along with the other. In the United States and in the British colonies the land tenure is allodial.

ALLOPATHY, a system of medicine—that ordinarily practiced—the object of which is to produce in the bodily frame another condition of things than that in or from which the disease has originated. If this can be done the disease, it is inferred, will cease. Allopathy is opposed to homœopathy, which aims at curing diseases by producing in antagonism to them symptoms similar to those which they produce; the homœopathic doctrine being that "like is cured by like."

ALLOPHYLIAN, in ethnology, a term introduced by Pritchard to characterize the nations or races of Europe and Asia not belonging to the Indo-European, the Syro-Arabian, or the Egyptian races. It has been generally superseded by Turanian.

ALLOWAY, Burns' birthplace, and the scene of his "Tam o' Shanter," lies on the right bank of the "bonny Doon" 2 miles S. of the town of Ayr. The "auld clay biggin," in which the poet was born on Jan. 25. 1759, was in 1880 converted into a Burns Museum. The "haunted kirk" still stands, a roofless ruin, near the "auld brig"; and close by is the Burns monument (1820).

ALLOY, a compound or mixture of two or more metals. When mercury is mixed with another metal, the compound is termed an amalgam. Alloys are divided into three groups: (1) Those formed by the metals lead, tin, zinc, and cadmium, which impart to their alloys their own physical properties in the proportions in which they themselves are contained in the alloy. (2) Those formed by almost all other metals. (3) Those which contain metals found in both these groups of alloys.

In every alloy the specific heat and the coefficient of expansion are always the means of those of its component metals. But in other physical properties a variation takes place. This is the case with specific gravity, which, in alloys of the first group, is the mean of their constituent metals; but in those of the second group it is always greater or less than the mean specific gravity of their constituents.

In some instances, when two melted metals are mixed together to form an alloy, an evolution of heat occurs which is believed to indicate that a chemical compound has been formed. This is the case with copper and zinc, copper and aluminum, platinum and tin. etc. The strength or cohesion of an alloy is generally greater than that of the mean cohesion of the metals contained therein or even of that of the most cohesive of its constituents.

The most useful alloy in the arts is brass. This compound metal is next to iron in importance.

There are some important alloys of copper and tin, among them bronze, gun metal, bell metal and speculum metal. In these the proportions vary from equal parts of copper and tin to 10 parts of copper with 1 of tin. The most cohesive, that is, the strongest of them, is a bronze consisting of 6 parts of copper to 1 of tin. Phosphor bronze is an invention of recent years. The addition of from 0.25 to 2.5 per cent. of phosphorus to a bronze containing from 7 to 8 per cent. of tin gives it greater hardness, elasticity, and toughness. This alloy is now much used for parts of machinery.

Pewter is a tin alloy which was more used formerly than now. Type metal is a compound of 50 parts of lead, 25 of antimony, and 25 of tin, but it varies slightly. Fusible metal melts at low temperatures; one kind is composed of 3 parts of tin, 5 of lead, and 8 of bismuth, and melts in hot water. This alloy is now a good deal employed in stereotyping, and in obtaining copies of woodcuts.

Aluminum bronze, very closely resembling gold in appearance, is much used for pencil-cases, chains, and some larger objects. A compound of silver and aluminum is sometimes used for watch-springs, and for spoons and forks. Dentists use a very ductile alloy composed of 2 parts by weight of silver and 1 of platinum.

When gold is to be used for coins, jewelry, or plate, it requires to be alloyed with copper or silver or with both, in order to harden it. Like silver, it is too soft when pure. There are five legal standards for articles made of gold—i. e., alloyed gold apart from coin. These are called 22, 18, 15, 12, and 9 carat gold. That is to say, these figures represent the number of parts of pure gold in every 24 parts of the alloy used by the goldsmith or jeweler. English sovereigns are made of a mixture of 22 parts of gold to 2 of copper, and this is called 22-carat or standard gold. In Germany, Italy, and the United States, standard gold for the coinage is 21.6 carats.