[Letter] 1906 Apr 13, Faculte des Sciences de Paris, rue Cuvier [to an unnamed correspondent]/Pierre Curie. 5p. on 2 leaves. [In French, with ts. English translation. Probably to G. D. Liveing. Discusses technical and economic probelms of extracting radium (principally), actinium, polonium and radioactive lead in the factory, mentioning suppliers. Compares factory methods with small-scale laboratory techniques; states that he and Mme. Curie have perfected a laboratory assay method for radium using radium emanation from dissolved salts]