The earth is collected from the surface of the most barren spots and formed into small, shallow, round tanks, a yard in diameter.

Water is then poured in, and the tank filled to the surface, with an additional supply of the earth, and smoothed over.

This tank is then left exposed to the sun for two days, during the hottest and driest months of the year.
March, April, and May, and part of June, when the crust, formed on the surface, is taken off.

The process is repeated once; but in the second operation the tank is formed around and below by the debris of the first tank, which is filled to the surface, after the water has been poured in, with the first _crust_ obtained.

The second crust is called the _reha_, which is carbonate or bicarbonate of soda.