To a suspension of 2 kg. dibenzylethylenediamine-tetracycline complex (activity 680 .gamma./mg.) in 2 l. H2O, HCl was added to pH 2.9, a soln. of 300 g. Na hexametaphosphate (I) in 3 l. H2O was added with stirring and the pH adjusted to 2.2, the supernatant layer, removed and treated with a soln. of 250 g. I in 2500 ml. H2O, the title compd., RC22H24N2O8.NaPO3.5HPO3 (II), was pptd. at pH 1.7, the mixt. stirred 1 hr., and II filtered, washed with H2O followed by MeOH, and dried. The K salt of II was also prepd. Activity of II was 808.gamma./mg.