Researchers found a way to separate arsenic (V) from arsenic (III) in hot spring waters using a chemical called MgNH4PO4·6H2O. They dissolved the separated arsenic in specific acids and measured it using a special method. Iron (III) and manganese (II) in the water made it harder to determine the amount of arsenic (V). They discovered that the oxidation number of arsenic in some samples was five.