Abstract: A method for generating hydrogen gas, an apparatus for producing hydrogen gas, and an energy conversion system, which are so designed as to generate hydrogen extremely efficiently without the help of catalyst are provided. The hydrogen gas is generated by decomposing a metal hydride in a mixture composed of said metal hydride, water, and a second solution which has a pH value lower than that of the aqueous solution of said metal hydride wherein the metal hydride is represented by a formula: ?z(1-x)?zx[BHy], where ? and ? are mutually different elements selected from Groups 1A, 2A, and 2B of the periodic table; and x, y, and z are defined respectively by 0?x?1, 3<y<6, and 0<z<3.

Abstract: A magnetic recording medium comprising a substrate made of non-magnetic material, and a magnetic layer formed on the substrate, the magnetic layer being composed primarily of a ferromagnetic powder and a binder, wherein an amount of a sulfuric ion extracted when the magnetic recording medium is immersed in a pure water having a temperature of 30.degree. C. for one hour, is 100 .mu.g or less per one square meter of the magnetic recording medium.