The Collaborative International Dictionary of English v.0.48:

Nitratine \Ni"tra*tine\, n. (Min.)
   A mineral occurring in transparent crystals, usually of a
   white, sometimes of a reddish gray, or lemon-yellow, color;
   native sodium nitrate. It is used in making nitric acid and
   for manure. Called also soda niter.
   [1913 Webster]