valuable amino alkane diphosphonic acids in which one or both hydrogen atoms of the amino group are substituted by hydroxy alkane groups , and their alkali metal salts and a process of using them are described . said compounds are highly water - soluble , are stable against hydrolysis even at temperatures exceeding 100 ° c ., and have a high sequestering power so that they can be used advantageously , for instance , in processing aqueous media of considerable hardness , and in suppressing scale and corrosion in aqueous media used for heat treatment of containers .