THE remarkable chemical analogy of the ammonium radicle and the alkali metals may be explained with the help of Bohr's theory of atomic structure. According to Bohr, the atom of nitrogen consists of a nucleus with a positive charge of 7e, surrounded by two rings of electrons, the inner containing 4, the outer 3 electrons. N is, therefore, represented by 7 (4, 3). Ordinary chemical compounds are supposed to be held together by rings of electrons rotating in planes perpendicular to the lines connecting the nuclei of the composing atoms; so that NH3 may be represented by (4, 3—3). This principle leads, however, to difficulties, if applied to NH4; a configuration (4, 3—4) seems impossible. It is better to suppose the nuclei and electrons to rearrange themselves within the atom. I assume, therefore, that the nuclei unite, or at least that they get quite close to each other, in the centre of the system, while the electrons arrange themselves in four rings (4, 4, 2, 1), rotating round the joined nuclei. It may seem difficult to bring the nuclei together against the repelling forces, but it must be remembered that the radicle NH4 can only be formed by indirect methods; in no circumstances will ammonia and hydrogen unite to form NH4. The co-operation of another molecule containing hydrogen, like H2O, HCl, is absolutely necessary, an intermediate compound first being formed, from which the ammoniumion is produced by electrolytic dissociation. Once liberated, the ammonium decomposes immediately; it is extremely unstable, exactly conforming to our expectations. It is also important to remark in this connection, that, according to Coehn, electric charges are given off during the decomposition.