Note 126 — Chapter XIII · ALKALI.

Black alkali is so called because the caustic solution containing sodium carbonate, in rising to the surface of the soil, dissolves and carries with it organic matter which is subsequently left on the surface in more or less blackish deposits, often ring-like in appearance. It is by no means uncommon, however, to find deposits of “black alkali” which are not black at all, and it is quite common to find “white alkali” so dark in color as to suggest the presence of sodium carbonate, although the latter be absent.