The following is but a short and incomplete account of a compound formed on the carbon and binding screws of a makeshift Leclanché battery. The cells employed were ordinary Bunsen elements, of which the carbon was embedded in manganese dioxide; the substance in question grew on the brass binding screws, and as a thin layer on the carbon. The external appearance of the mass was reniform, the colour ranging from a pale blue to a dark purple and lilac tint; the portions from the carbon were of a pale green shade, and of no special shape. The quantity being small, it was impossible to make more than one analysis of each substance and that only with very small quantities.