isomorphous

[Pref. iso-, and Gr. morphe =a form, and Eng. suff. -ous.] Chem. A term applied to certain substances, which have the same crystalline form, and are also analogous in their chemical constitution. The alums, for instance, no matter what their compos i tion, all crystallize in octahedra, and if we place a the other hand, the po e ion of an equal number of atoms is not e ential to isomorphism, for two atoms of one element are not unfrequently isomorphous with one atom of another element; and sometimes a molecular group is isomorphous in its combinations with an elementary atom-NH, with K, for example. There are also numerous examples of bodies crystallizing in the same form, but with out exhibiting any similarity of chemical constitution." Isomorphous bodies are generally arranged according to the crystallographic systems. The elements belong to the monometric system, with the exception of arsenic, antimony, and bismuth, which belong to the hexagonal. The protoxides, the proto-chlorides, bromides, and iodides, and the proto-sulphides are also monometric. The carbonates belong partly to the trimetric, and partly to the hexagonal, the nitrates to the hexagonal and the monometric, and the alums to the monoclinic systems. When the same body is found to crystallize in two different forms, it is said to be dim or. pho us. [CRYSTALLOGRAPHY, CRYSTALS.]