The purgative effect of the waters of Epsom, in southern England, was first discovered in the early seventeenth century. Epsom subsequently developed as one of the great English spas where high society flocked to take the medicinal waters. The extraction of the Epsom Salts from the spa waters and their chemical analysis, the essential feature of which was magnesium sulphate, were first successfully carried out by Doctor Nehemiah Grew, distinguished as a physician, botanist and an early Fellow of the Royal Society. His attempt to patent the production and sale of the Epsom Salts precipitated a dispute with two unscrupulous apothecaries, the Moult brothers. This controversy must be set against the backcloth of the long-standing struggle over the monopoly of dispensing of medicines between the Royal College of Physicians and the Worshipful Society of Apothecaries of London.