Spirit of Hartshorn

Spirit of Hartshorn was traditionally made by heating shavings or filings of deer antler, hart's horn, in a closed retort without air, a process called dry distillation that drove off a pungent, alkaline smelling vapor which was condensed and collected as a liquid or absorbed into water. Antler and bone are rich in nitrogenous organic matter, and destructive distillation of any such material, not only deer horn specifically, yields a broadly similar volatile alkaline product, so later manufacturers increasingly used bones, hooves and other animal waste as cheaper substitutes while keeping the traditional name. The resulting spirit was strongly alkaline, sharply pungent, and effective at neutralizing acids, properties that made it useful both in the chemical workshop and, diluted and perfumed, as smelling salts, sal volatile, kept on hand to revive someone who had fainted by stimulating the nasal passages.

In pharmacy it was prescribed for a range of complaints understood in the period as related to weak or sluggish vital spirits, and its ability to snap a fainting person back to alertness gave it a lasting reputation independent of any deeper theoretical justification. As an alkali, it was also useful in the laboratory for neutralizing acid preparations and for precipitating certain metal salts from solution.

Spirit of Hartshorn is identified as an aqueous solution of ammonia, NH3 dissolved in water, an identification supported both by its preparation, the dry distillation of nitrogen rich animal matter being a genuine and still recognized route to ammonia, and by its characteristic properties, alkalinity, a sharp irritating smell, and effectiveness as a smelling salt, all of which match ammonia's known chemistry closely.

Ammonia's status as the shared chemical basis of both spirit of hartshorn and sal ammoniac, despite their very different preparations, one from animal horn and one from soot and dung, was itself an important early clue that helped eighteenth century chemists recognize ammonia as a single definite substance obtainable by several different routes rather than a family of vaguely related volatile alkalis, a conceptual step that mirrors, on the alkaline side of chemistry, the parallel recognition of oil of vitriol as a single acid obtainable from several vitriols. Spirit of hartshorn's continued sale as smelling salts well into the twentieth century, long after its animal-horn origin had been replaced by cheaper industrial ammonia sources, shows how thoroughly a traditional name can outlive the specific process that first gave rise to it.