n Oude, carbonates
of soda, used in making _glass_ and _soap_, are taken. 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. This is
formed into small cakes, which are baked to redness in an oven, or
crucible, to expel the moisture and carbonic acid which it contains.
They are then powdered to fine dust, which is placed in another
crucible, and fused to liquid glass, the _reha_ containing in itself
sufficient silica to form the coarse glass used in making bracelets,
&c.

A superabundance of nitrates seem also to impair or destroy fertility
in the soil, and they may arise from the decomposition of animal or
vegetable matter, in a soil containing a superabundance of porous
lime. The atmospheric air and water, contained in the moist and
porous soil, are decomposed. The hydrogen of the water combines with
the nitrogen of the air, and that given off by the decomposing
organic bodies, and forms ammonia. The nitrogen of the ammonia then
takes up the oxygen of the air and water, and becoming nitric acid,
forms nitrates with the lime, potash, soda, &c., contained in the
soil. Without any superabundance of lime in the soil, however, the
same effects may be produced, when there is a deficiency of decaying
vegetable and animal matter, as the oxygen of the decomposed air and
water, having no organic substances to unite with, may combine with
the nitrogen of the ammonia, and form nitric acid; which, uniting
with the lime, potash, soda, &c., may form the superabounding
nitrates destructive of fertility.

This superabundance of reha, or carbonate of soda, which renders so
much of the surface barren, must, I conclude, arise from deposits of
common salt, or chloride of sodium. The water, as it percolates
through these deposits towards the