This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Ammonia exists in the air in minute quantity (probably as carbonate), in sea-water and many mineral waters, and rain-water; in the soil and in animal excretions, especially the urine. It is a usual product of decomposing nitrogenous matter, and is said to occur free in certain plants, as in the leaves of aconite and the root of hellebore. The chloride is found native near volcanoes, and in many coal mines.
Its salts are commonly obtained from "gas-liquor," a product of the distillation of coal in gas-manufacture: when this is neutralized by hydrochloric acid, it yields a chloride, NH1C1 (sal-ammoniac), and from this salt, when purified are derived all the other ammonium compounds used in medicine.
Ammonia itself is a colorless gas, which may be liquefied. It has a pungent odor and alkaline reaction; it forms salts with acids, and, as these are very analogous in chemical relations to salts of potash and soda, it is believed that they have a metallic base, which is named ammonium, and is the fundamental radical of the series. But while potassium and sodium are simple, ammonia is a compound body or radical (NH1), acting like a simple one, and until its recent isolation as a blue liquid, its existence was inferred rather than demonstrated (Smith's Commentary).