ALLIGA′TION. Syn. Alliga′tio, L. In commercial arithmetic, a rule for ascertaining the price or value of mixtures, and for determining the proportions of the ingredients that must be taken to produce mixtures of any given price, value, or strength. The first is called ALLIGATION ME′DIAL; the second, ALLIGATION ALTERN′ATE. Its principles and applications are explained under Mixtures (Arithmetic of).
ALLOP′ATHY. Syn. Allopa′thia, L. (from ἁλλος, other, different, and παθος, affection or disease, Gr.); Allopathie, Fr. In medicine, the method of curing disease by the use of remedies which tend to produce a condition of the system, either differing from, opposed to, or incompatible with the condition believed to be essential to the disease it is sought to cure. It is commonly employed to distinguish the ordinary system of medical practice from homœopathy (which see). Hence (an) ALLOP′ATHIST, and the corresponding adjective ALLOPATH′IC (allopath′icus, L.).
ALLOT′ROPY. Syn. Allot′ropism; Allotro′pia, Allotropis′mus, L. Literally, a difference in character; another form of the same substance. In chemistry, a term invented, by Berzelius, to express the state or condition, or the change of character, assumed by certain substances at different temperatures, or under different treatment, whilst their nature and composition continue the same. It more particularly relates to colour, hardness, solubility, texture, &c. Boron, carbon, silicon, iron, sulphur, and phosphorus, afford striking examples of the changes here referred to.
ALLOX′ANTIN. C8H4N4O7.3H2O. A crystallisable substance, first obtained by Dr Prout from uric acid.
Prep. 1. Uric acid, 1 part; is boiled in water, 32 parts; dilute nitric acid being added until solution is complete; the resulting liquid is evaporated to 2⁄3rds its volume, and then set aside for 10 or 12 hours; the crystals, which are deposited, are purified by re-solution and crystallisation.
2. Sulphuretted hydrogen gas is passed, in a full stream, through a moderately strong aqueous solution of alloxan, in the cold. The alloxantin, which is deposited as a crystalline mass, is purified by draining, cautious washing with cold water, re-solution in boiling water, and re-crystallisation. The impure mother-liquor from which crystals of alloxan have separated, if diluted with water, may be used for this purpose.
Prop., &c. Crystals, small colourless, transparent, four-sided, oblique rhombic prisms; scarcely soluble in cold water; solution reddens litmus; with baryta water it gives a characteristic violet-coloured precipitate, which disappears on heating; and with nitrate of silver a black precipitate of that metal; the crystals are reddened by ammoniacal vapours.
ALLOY′. Syn. Alliage, Fr.; Legirung, Vermischung durch schmelzen, Ger. In coinage, a compound of the precious metals with another, or others, of less value; also the least valuable metal, or metals, in such compounds. In chemistry and metallurgy, combinations of the metals with each other usually obtained by fusion. When mercury is one of
the component metals, the compound is termed an AMALGAM.
Prep., &c. No General rules can be given for this purpose. Alloys of metals differing greatly in fusibility, are commonly made by adding the more fusible one, either in the melted state, or in small portions at a time, to the other melted, or heated to the lowest possible temperature at which a perfect union will take place between them. The mixture is usually affected under a flux, or some material that will promote liquefaction, and prevent volatilisation and unnecessary exposure to the air. Thus, in melting lead and tin together, for solder, resin, or tallow is thrown upon the surface; in tinning copper, the surface is rubbed with sal ammoniac; and in combining some metals, powdered charcoal is used for the same purpose. Quicksilver combines with many metals in the cold, forming AMALGAMS.