Chem. [a. mod.L. ammōnium, formed by Berzelius, 1808, on AMMONIA, after analogy of soda, sodium, magnesia, magnesium, and the names of the recent metals generally.] The radical supposed to exist in the salts of ammonia, a compound of 4 equivalents of hydrogen with 1 of nitrogen, NH4, which behaves in composition as a monatomic alkaline metal, replacing, and presenting close analogies to, sodium and potassium.
1808. Sir H. Davy, in Phil. Trans., XCVIII. 364. From platina to potassium there is a regular order of gradation as to physical and chemical properties, and this would probably extend to ammonium, could it be obtained in the fixed form.
1850. Daubeny, Atom. The., ix. 295. The atomic volume which these lighter metals, viz. ammonium, barium, calcium … have.
1875. Ure, Dict. Arts, I. 142. Although it may be objected … that the metal ammonium is not known, yet a curious metallic compound of this metal with mercury has been obtained.
b. attrib. In names of compounds in which ammonia was formerly, and is still often, used, as ammonium salts, carbonate, chloride, phosphate. Also ammonium alum (see ALUM 2); ammonium amalgam, a soft solid metallic substance, an amalgam of ammonium and mercury, analogous to the sodium and potassium amalgams.
1863. Watts, Dict. Chem. (1872), I. 188. Ammonium-salts are isomorphous with potassium salts. Ibid., 195. Spoken of as ammonium-bases in contradistinction to the amine- or ammonia-bases.
1869. Roscoe, Elem. Chem., 214. Ammonium Chloride, or sal-ammoniac.
1873. Williamson, Chem., viii. § 52. The ammonium amalgam very rapidly decomposes when removed from the liquid.
