black alkali

1 definition found

black alkali - Collaborative International Dictionary of English v.0.48 :

  Alkali soil \Alkali soil\
     Any one of various soils found in arid and semiarid regions,
     containing an unusual amount of soluble mineral salts which
     effloresce in the form of a powder or crust (usually white)
     in dry weather following rains or irrigation. The basis of
     these salts is mainly soda with a smaller amount of potash,
     and usually a little lime and magnesia. Two main classes of
     alkali are commonly distinguished: black alkali, which may
     be any alkaline carbonate, but which practically consists of
     sodium carbonate (sal soda), which is highly corrosive and
     destructive to vegetation; and white alkali, characterized
     by the presence of sodium sulphate (Glauber's salt), which is
     less injurious to vegetation. Black alkali is so called
     because water containing it dissolves humus, forming a
     dark-colored solution which, when it collects in puddles and
     evaporates, produces characteristic black spots.
     [Webster 1913 Suppl.]