Phosphates Phosphates may be created by substituting some or all of the hydrogen of a phosphoric acid by metals. Depending on the number of hydrogen atoms that are replaced, the resulting compound is described as a primary, secondary or tertiary phosphate. Primary and secondary phosphates contain hydrogen and are acid salts. Secondary and tertiary phosphates, with the exception of those of sodium, potassium and ammonium are insoluble in water. Tertiary sodium phosphate is valuable as a detergent and water softener. The primary phosphates tend to be more soluble. Phosphates, which are an important component