Both saltpetre and common salt are made by lixiviation from some of the poor oosur soils; but, from the most barren in 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 surface, becomes saturated with their alkaline salts; and, as it reaches the surface and becomes evaporated in the pure state, it leaves them behind at or near the surface.  On its way to the surface, or at the surface, the chloride of sodium becomes decomposed by contact with carbonates of ammonia and potassa—­sulphuric and nitric acids.  In a soil well supplied with decaying