IN connexion with the letters from F. J. Garrick and from Dr. J. S. Anderson, N. L. Spoor and Prof. H. V. A. Briscoe published in NATURE of March 20, 1937 (p. 507), Prof. A. A. Grünberg, Kovensky pereulok 22, log. 12, Leningrad, has been good enough to give references to several papers by himself and his collaborators which are for the most part inaccessible to English readers. In these, during the last seven years, it has been shown experimentally that the ammines of platinum and rhodium may undergo acid-dissociation by a mechanism similar to that inferred from the exchange experiments on cobalt ammines. Prof. Briscoe and his collaborators state that they are glad to learn that their entirely independent experiments afford, both qualitatively and quantitatively, so satisfactory a confirmation of the findings and predictions Prof. Griinberg has already published. Of the more recent references he gives, one (A. A. Grünberg and D. T. Rjabtschikoff, Acta Physico-Chimica, 3, No. 5, 555 ; 1935), which is in German, and may be seen in a few British libraries, should certainly be consulted by chemists interested in this subject.