Thus sulphuric and carbonic acids yield
NaHSO_{4}, acid sulphate or bisulphate of soda, and NaHCO_{3},
bicarbonate of soda, respectively. An example of a tribasic acid is
phosphoric acid, H_{3}PO_{4}, and here we may have three different
classes of salts of three various degrees of basicity or
base-saturation. We may have the first step of basicity due to
combination with soda, NaH_{2}PO_{4}, or monosodium phosphate, the
second step, Na_{3}HPO_{4}, or disodium phosphate, and the third, and
final step, Na_{3}PO_{4}, or trisodium phosphate. Now let us turn to the
varying degrees of acidity, or rather the proportions of acid radicals
in salts, due to the varying appetites or combining powers of bases.
Sodium only forms simple monoacid salts, as sodium chloride (NaCl),
sodium sulphate (Na_{2}SO_{4}); calcium forms diacid salts, _e.g._
calcium chloride (CaCl_{2}); and aluminium and iron, triacid salts, for
example, aluminium sulphate [Al_{2}(SO_{4})_{3}] and iron (ferric)
sulphate [Fe_{2}(SO_{4})_{3}]. Now in these triacid salts we can remove
some of the acid groups and substitute the elements of water, OH, or
hydroxyl, as it is called, for them.
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