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.