Electromagnetically separated Mg 24, Mg 25, Mg 26 isotopes were bombarded with Po α-particles. In the case of Mg 25 and Mg 26 the excitation function of γ-radiation from the nuclear processes was measured with a thin target. In the case of the Mg 25 target, resonances were found at α-energies of 3.58, 4.33, 4.47, 4.61, 4.80, 4.99 and 5.09 MeV; in the case of Mg 26 target, at α-energies of 4.56 and 5.01 MeV. From these data seven highly excited states of the Si 29 compound nucleus and two of the Si 30 nucleus were determined. The origin of γ-radiation was cleared up by the observed spectra of γ-rays. A method for a micro-electro-chemical deposition of Mg has been elaborated by the author.