R_{2}O_{2} or RO; salts RX_{2}, hydroxides R(OH)_{2}. The most simple basic salts R_{2}OX_{2} or R(OH)X; for instance, the chloride Zn_{2}OCl_{2}; also an almost exclusively basic type; but the basic properties are more feebly developed than in the preceding type. For example, CaO, MgO, BaO, PbO, FeO, MnO, &c. R_{2}O_{3}; salts RX_{3}, hydroxides R(OH)_{3}, RO(OH), the most simple basic salts ROX, R(OH)X_{3}. The bases are feeble, like Al_{2}O_{3}, Fe_{2}O_{3}, Tl_{2}O_{3}, Sb_{2}O_{3}. The acid properties are also feebly developed; for instance, in B_{2}O_{3}; but with the non-metals the properties of acids are already clear; for instance, P_{2}O_{3}, P(OH)_{3}. R_{2}O_{4} or RO_{2}; salts RX_{4} or ROX_{2}, hydroxides R(OH)_{4}, RO(OH)_{2}. Rarely bases (feeble), like ZrO_{2}, PtO_{2}; more often acid oxides; but the acid properties are in general feeble, as in CO_{2}, SO_{2}, SnO_{2}. Many intermediate oxides appear in this and the preceding and following types. R_{2}O_{5}; salts principally of the types ROX_{3}, RO_{2}X, RO(OH)_{3}, RO_{2}(OH), rarely RX_{5}. The basic character (X, a halogen, simple or complex; for instance, NO_{3}, Cl, &c.) is feeble; the acid character predominates, as is seen in N_{2}O_{5}, P_{2}O_{5}, Cl_{2}O_{5}; then X = OH, OK, &c., for example NO_{2}(OK). R_{2}O_{6} or RO_{3}; salts and hydroxides generally of the type RO_{2}X_{2}, RO_{2}(OH)_{2}. Oxides of an acid character, as SO_{3}, CrO_{3}, MnO_{3}. Basic properties rare and feebly developed as in UO_{3}. R_{2}O_{7}; salts of the form RO_{3}X, RO_{3}(OH), acid oxides; for instance, Cl_{2}O_{7}, Mn_{2}O_{7}. Basic properties as feebly developed as the acid properties in the oxides R_{2}O. R_{2}O_{8} or RO_{4}. A very rare type, and only known in OsO_{4} and RuO_{4}.