Sociktk suisse de chimie, Bile -Societk svizzera di chimica, Basilea Nachdruck verboten -Tous droits rkserv6s -Printed by Birlrhauser AG., Basel Summary. The preparation and probable structure of manganese (111)-manganate (IV)Mn,0,,,5H20 (a, = 2,84, co = 7,27 A) and manganous(I1)-manganate(1V) Mn70,,,6H,0 are described. Both consist of platelets. Digesting in diluted HNO, leads to y-MnO, (nsutite). Manganese (111)-manganate (IV) is much less stable than the sodiummanganese (11, 111)-manganate-(IV) described earlier and looses water easily when heated or in vacuo. Water loss results in breaking down of the double layer lattice, and the product is only two-dimensionally ordered, producing only prism reflections on the X ray diagramm. Heating results in a continuous transition to the two-dimensionally ordered phase, then to a finely divided and very disordered y-MnO,, and eventually to a finely divided and disordered B-MnO, (pyrolusite). The transition is topotactical so far, but further heating produces cr-Mn,O, without obvious topotactical relations to the earlier products. The so-called '6-Mn0,' (birnessite) appears to be a family of finely divided and very disordered varieties of such manganates(1V) with part of the Mn3+ substituted by Mn4+. Since such products usually contain remarkable amounts of alkali ions, they are rather varieties of the earlier described sodiummanganese (11, 111)-manganate (IV). A provisional explanation of the streaking in the electron diffractions of these manganates (IV) is given. With respect to these results the socalled ' 8-MnO,' can no longer be attributed t o the true manganese dioxides.
