In 1925, he observed weak radioactivity in a sample of potassium, another alkali metal, and incorrectly concluded that eka-caesium was contaminating the sample (the radioactivity from the sample was from the naturally occurring potassium radioisotope, potassium-40).
În 1925, el a observat semne de radioactivitate slabe într-o monstră de potasiu, alt metal alcalin, concluzând incorect că eka-cesiul era cel ce contamina proba (de fapt, radioactivitatea provenea de la izotopul potasiu-40, ocurent natural).