Ammonium persulfate is a white, crystalline salt consisting of technically pure ammonium peroxodisulfate. It is used as an initiator (source of free radicals) for the polymerization of monomers and as a strong oxidizing agent in many applications. It has the particular advantage of having a good storage stability as a result of its extremely high purity and of being easy and safe to handle. Due to its hygroscopic character APS tends to lump, especially in humid atmosphere and can be optionally supplied with an addition of silicic acid.