ed forces
its way through the dough, thus making it porous and light.

~Sodium nitrate~ (_Chili saltpeter_) (NaNO_{3}). This substance is found
in nature in arid regions in a number of places, where it has been
formed apparently by the decay of organic substances in the presence of
air and sodium salts. The largest deposits are in Chili, and most of the
nitrate of commerce comes from that country. Smaller deposits occur in
California and Nevada. The commercial salt is prepared by dissolving the
crude nitrate in water, allowing the insoluble earthy materials to
settle, and evaporating the clear solution so obtained to
crystallization. The soluble impurities remain for the most part in the
mother liquors.

Since this salt is the only nitrate found extensively in nature, it is
the material from which other nitrates as well as nitric acid are
prepared. It is used in enormous quantities in the manufacture of
sulphuric acid and potassium nitrate, and as a fertilizer.

~Sodium phosphate~ (Na_{2}HPO_{4}.12H_{2}O). Since phosphoric acid has
three replaceable hydrogen atoms, three sodium phosphates are
possible,--two acid salts and one normal. All three can be made without
difficulty, but disodium phosphate is the only one which is largely
used, and is the salt which is commonly called sodium phosphate. It is
made by the action of phosphoric acid on sodium carbonate:

Na_{2}CO_{3} + H_{3}PO_{4} = Na_{2}HPO_{4} + CO_{2} + H_{2}O.

It is interesting as being one of the few phosphates which are soluble
in water, and is the salt commonly used when a soluble phosphate is
needed.

~Normal sodium phosphate~ (Na_{3}PO_{4}). Although this is a normal salt
its solution has a strongly alkaline reaction. This is due to the fact
that the salt hydrolyzes in solution into sodium hydroxide and disodium
phosphate, as represented in the equation

Na_{3}PO_{4} + H_{2}O = Na_{2}HPO_{4} + NaOH.

Sodium hydroxide is strongly alkaline, while disodium phosphate is
nearly neutral in reaction. The solution as a whole is therefore
alkaline. The salt is prepared by adding a large excess of sodium
hydroxide to a solution of disodium phosphate and evaporating to
crystallization. The excess of the sodium hydroxide reverses the
reaction of hydrolysis and the normal salt crystallizes out.

~Sodium tetraborate ~(_borax_) (Na_{2}B_{4}O_{7}.10H_{2}O). The properties
of this important compound have been discussed under the head of boron.

POTAS