a process for preparing concentrated solutions of hydroxylammonium nitrate or hydroxylammonium perchlorate which comprise reacting hydroxylammonium sulfate with either barium nitrate or barium perchlorate , in such a way that the dissolved barium salt is reacted with the dissolving hydroxylammonium sulfate while agitating the system so as to keep the slurried barium salt from directly contacting the hydroxylammonium sulfate . the rate of addition of the hydroxylammonium sulfate is slower than the rate of solution of the barium salt . an excess of barium nitrate or barium perchlorate ions is needed in the solution to which the hydroxylammonium sulfate is added until the reaction is terminated . the concentration of the han or hap in the final solution can be increased still further if a solution of han or hap is respectively used in forming the barium salt slurry .