If the sample contains less than 10 parts per million of manganese, use
a colorimetric method in which the manganous salt is oxidized to
permanganate and the color produced thereby is compared with that of a
standard solution similarly treated. The persulfate method and the
bismuthate method are suitable. If the sample contains more than 10
parts per million of manganese it is sometimes preferable to use a
volumetric or gravimetric method.