Concentrated Cu (I)-sulfamate solutions may be obtained by chemical or electrochemical methods applied to Cu(NH₂SO₃)₂ baths, in particular by reaction of these baths on metallic copper, or by electrolyzing them in continuous or alternative current. From these solutions, crystalline, quite stable, new cuprous compounds may be separated. These may be utilized in all of the application fields of the cuprous compounds, for instance to prepare Cu₂O, metallic copper powder and so on. The high Cu (I) content attainable in sulfamate baths has allowed a thorough investigation of the cuprous-ions participation in electrode processes (overvoltages, current efficiency, throwing power, anodic slimes and so on).