Allot′ment System, the system of allotting small portions of land (an acre or less) to farm-labourers or other workers, to be cultivated after their regular work by themselves and their families, a system believed by many to be calculated greatly to improve their condition. An Allotment Act for England, passed in 1887, authorizes the sanitary authorities in any locality to determine if there is a sufficient demand for allotments there, and to acquire land to be let to the labouring population resident in their district. Such land may be compulsorily acquired, due compensation being given; but land belonging to a park, pleasure-ground, &c., is not to be so acquired. No person is to hold more than 1 acre as an allotment; and the rents are to be fixed at such amount as may reasonably be deemed sufficient to guarantee the sanitary authority from loss. No building is to be erected on any allotment other than a tool-house, pig-sty, shed, or the like. In the Allotment Acts of 1887 and 1892 (Scotland) the definition is applied to a plot of land not exceeding 1 acre, but the Local Government Act of 1894 authorized the letting of an allotment up to the area of 4 acres to one person, while the Small Holdings and Allotments Act of 1907 definitely extends the limit of an allotment to 5 acres. The distinction between allotments and small holdings has therefore been obliterated, at least as far as England and Wales are concerned. County councils will let plots of 1 to 5 acres as small holdings, and parish councils as allotments. During the European War 183,000 allotments were registered under the Cultivation of Lands Order, and the number of allotments in Great Britain not exceeding 1 acre now amounts to over 1,000,000. In proportion to the total agricultural area or population it is much smaller in Scotland than in England. The rents of allotments vary greatly, and near towns, or even villages, they are very high, often from £4 to £8 per acre. A measure corresponding to the English Small Holdings and Allotments Act of 1907 was passed for Scotland in 1911, and came into operation in 1912. In recent years a large number of co-operative allotment associations have come into existence.
Allot′ropy (Gr. allos, other, tropos, manner), a term used by Berzelius to express the fact that one and the same element may exist in different forms, differing widely in external physical properties. Thus carbon occurs as the diamond, and as charcoal and plumbago, and is therefore regarded as a substance subject to allotropy.
Al′loway, a parish of Scotland, now included in Ayr parish. Here Burns was born in 1759, and the "auld haunted kirk", near his birthplace, was the scene of the dance of witches in Tam o' Shanter.
Alloy′ is the substance produced by melting together two or more metals. Sometimes a chemical compound is formed, but more generally one metal is interspersed throughout the other, much as sugar is through water in which it is dissolved. In this case the alloy is called a 'solid solution' of one metal in another. Many metals mix together in all proportions, others only in certain proportions, while some will not mix in any proportion.
Scientific research has led to great advances in the use of alloys industrially. An alloy differs from its components in most of its physical properties, such as its hardness, ductility, strength, melting-point, and colour. The minutest trace of certain metals frequently produces an extraordinary change in the property of the body with which it is mixed. For instance, if bismuth is present in copper to the extent of more than 0.5 per cent, the copper cannot be used successfully in the construction of electrical machinery. Frequently the addition of a small proportion of a metal produces highly-desirable effects in one direction, but is deleterious in other directions. For instance, the presence of a small amount of manganese in cast-iron gives clean castings, but the magnetic qualities of the material are impaired.
Alloys are classified as ferrous and non-ferrous alloys.
Ferrous Alloys.—These alloys are of great industrial importance, as they include cast irons and steels. Pure iron is very little used in industry. Ordinary cast iron contains iron and about 3 per cent of carbon. The ordinary wrought iron of the blacksmith contains less than 0.25 per cent of carbon. Cast iron is brittle, and unreliable when used to sustain tensile stresses, and it cannot be forged; but wrought iron can be safely used in tension, is not brittle, and can be forged. The raw material from which steel is
made is cast iron or wrought iron. (For manufacture of steel see Steel.) The properties of steel can be varied within very wide limits by adding to it traces of certain metals. For instance, the addition of nickel up to 5 per cent makes the steel much stronger and tougher; the addition of tungsten up to about 19 per cent makes it hard (tool-steel, magnet steel), while molybdenum has a similar effect. Chromium and vanadium have a 'stabilizing' effect, i.e. tend to make large masses of the alloy homogeneous, and to make the alloy retain its hardness over wide ranges of temperature. Cobalt has a similar stabilizing effect. Molybdenum high-speed steel is more expensive than tungsten high-speed steel, but is said to wear better.
Non-ferrous Alloys.—Of the non-ferrous alloys the most important have copper as the basic metal. They do not become rusty on exposure. Copper, when used for electrical purposes, must be nearly pure. It is deposited electrolytically (see Electrolysis) and then made into bars (electrolytic copper).
Brass is an alloy of copper and zinc and varies much in composition. The best-known varieties are:—