What is "baker's salt"

Baker \Bak"er\, n. [AS. b[ae]cere. See Bake, v. t.]

1. One whose business it is to bake bread, biscuit, etc.

2. A portable oven in which baking is done. [U.S.]

   A baker's dozen, thirteen.

   Baker foot, a distorted foot. [Obs.]
   --Jer. Taylor.

   Baker's itch, a rash on the back of the hand, caused by the irritating properties of yeast.

   Baker's salt, the subcarbonate of ammonia, sometimes used instead of soda, in making bread.