In a paper already communicated to the Society by one of us attention was drawn to the fact that, in presence of a soluble silver salt, ammonium persulphate is decomposed with formation of nitric acid as well as sulphuric acid. The action had at that time been studied only in a roughly quantitative way, and it was therefore thought that a more exact study of the velocity of the reaction, and of the influence exerted by other salts present in solution, might prove of interest, and also throw light on the course which the reaction follows.