1) The PH ranges which regulate three types of the Goethite to be produced when the ferrous sulfate solution is mixed with sodium hydroxide soluton, are determined as fottows ;
at PH = 5.4～1.0 ; pale yellow and needle-like crystalline.
at PH = 13.2～5.4, orange yellow and bar-or needle-like crystalline.
at PH = 13.6～13.2, pale yellow and needle-like crystalline.
where, in each PH, the first terms indicate those PH value that two solutions are mixed, and the second terms are PH values gained when the oxydizing reactions of those mixed solutions by air-blowing are ended.
2) The optimum conditions to gain the needle-like and 0.5×0.1μ size crystalline for tape-racording are given.
3) The cobalt-ferrite crystalline obtained by wett method and treated at 600°～700℃ gives much higher Br and Hc values.

前報により山陰砂鉄還元鉄粉より純度高き硫酸第一 鉄を製造したがこの報告は，その硫酸第一鉄より録音用磁性酸化鉄及び複合酸化物の製造法及び諸性質を研究した。