Heusler Alloys, the group of ferromag netic manganese alloys, named after F. Hens ler, who discovered them in 1898. In addition to manganese or manganese-copper, these al loys contain one or more of the elements aluminum, antimony, arsenic, bismuth, boron, and tin. The aluminum-manganese-copper al loys show the largest degree of ferromagnet ism, about one-third that of the purest soft iron. The ternary tin-manganese bronzes also exhibit marked ferromagnetism. Manganese tin is magnetic and remains so when copper is added. Manganese-copper is non-magnetic, but becomes magnetic when tin is added. Re search has determined in the case of the aluminum-manganese bronzes that the chemi cal compound carrying the magnetism is ex pressed by the formula Alx(Mn,Cu)s. This seems to establish the fact that ferromagnet ism is a molecular phenomenon due to a con dition of definite chemical combination. See FERROMAGNETISM.
Pyrophoric Alloys.— The alloys distin guished by the title apyrophoric* have the pe culiarity of emitting hot sparks when rasped off with a coarse file. They consist of the cerium group of rare earth metals in alloy with iron, nickel, manganese or cobalt. They exhibit the same property in a less degree with cadmium, zinc, tin and lead. The common form of pyrophoric alloy used in automatic gas lighters contains 35 per cent of iron and 65 per cent of the cerium metals. These al
loys may, however, range in constitution from 10 per cent iron to 65 per cent iron. The py rophoric property of these alloys is utilized in gunnery, the alloy being set into the shell of the projectile. The friction due to the rapid ity of passage through the air is sufficient to ignite the alloy, thus marking the flight of the projectile by a trail of sparks.
See also ALUMINUM ; AMALGAM ; BaAss; BRONZE; FUSIBLE METALS; STEEL; and para graphs on Alloys under the titles of the dif ferent metals.
Buchanan, J. F., 'Practi cal Alloying' (Cleveland, Ohio, 1910) ; Field, S., 'Principles of Electro-Deposition> (London 1911) ; Gulliver, G. H., Alloys: Their Structure and Constitution> (London 1913) ; Hiorns, A. H., Metals' (New York 1912) ; Johnstone, S. J., 'Rare Earth In dustry> (London 1915) ; Law, E. F., and Their Industrial Applications' (London 1909) ; Roberts-Austen, Sir W. C., (Introduc tion to the Study of Metallurgy' (London 1910); Rosenhain, W., 'Metallurgy' (New York 1914); Ruer, R., 'The Elements of Metallurgy) (New York 1909). A very com plete bibliography of recent investigations as to Alloys up to 1 Jan. 1917 may be consulted in Metallurgical and Chemical Engineering (Vol. XVI, pp. 273-279).