The Collaborative International Dictionary of English v.0.48:

Hartshorn \Harts"horn`\ (-h[^o]rn`), n.
   1. The horn or antler of the hart, or male red deer.
      [1913 Webster]

   2. Spirits of hartshorn (see below); volatile salts.
      [1913 Webster]

   Hartshorn plantain (Bot.), an annual species of plantain
      (Plantago Coronopus); -- called also buck's-horn.
      --Booth.

   Hartshorn shavings, originally taken from the horns of
      harts, are now obtained chiefly by planing down the bones
      of calves. They afford a kind of jelly. --Hebert.

   Salt of hartshorn (Chem.), an impure solid carbonate of
      ammonia, obtained by the destructive distillation of
      hartshorn, or any kind of bone; volatile salts. --Brande &
      C.

   Spirits of hartshorn (Chem.), a solution of ammonia in
      water; -- so called because formerly obtained from
      hartshorn shavings by destructive distillation. Similar
      ammoniacal solutions from other sources have received the
      same name.
      [1913 Webster]