THE CHEMICAL GAZETTE, No. CCCXC1V.—March 15, 1859. SCIENTIFIC AND MEDICINAL CHEMISTRY. On Solutions of Sesquisalts of Manganese. By H. Rose. Sesquioxide of manganese is a very weak base, which is separated from many of its saline compounds in the form of hydrate, even by water. As Carius has shown, sesquioxide of manganese only dis solves in an excess of sulphuric acid when it contains protoxide; it then furnishes a purple-red solution. From the solution of this double salt the sesquioxide of manganese is only thrown down by a large quantity of water, in consequence of the great amount of free acid. The precipitation is complete, and the filtered solution contains only protoxide of manganese. The solutions of sesquioxide of manganese in oxyacids have so close a resemblance to a solution of permanganate of potash, that this oxide in them has frequently been regarded as a modification of permanganic acid. The solution of the sesquiphosphate of man ganese exhibits the most remarkable behaviour. If sesquioxide, proto-peroxide, or peroxide of manganese, manga- nates, or permanganates be heated with syrupous phosphoric acid, they dissolve in it. When the heat is continued until the acid begins to be volatilized a little, the mass, while hot, has a fine deep blue colour, like that communicated to fluxes by oxide of cobalt. On cooling, the mass becomes of a beautiful purple colour; with water it furnishes a solution of the same colour, exactly similar to a solu tion of permanganate of potash. It, however, contains sesquioxide of manganese, which is protected from precipitation by water by the phosphoric acid, by which it acquires a great stability, is not decom posed even by long boiling, and exhibits a different behaviour towards reagents in general, as indeed phosphoric acid usually acts in this respect upon many metallic oxides in the same way as tar taric acid and other organic acids. Hydrate of potash produces a brown precipitate in the solution ; the supernatant fluid is colourless. Chem. Gaz, 1859. G