_First procedure._—Prepare standards containing amounts of standard iron
solution ranging from 0.05 to 4 cc. according to the quantity of iron in
the sample. Dilute these amounts with water to about 40 cc. Add 5 cc. of
dilute hydrochloric acid and 3 drops of potassium permanganate to each
tube and dilute to 50 cc. Add 5 cc. of the potassium sulfocyanide to
each of the standard solutions at the same time that it is added to the
samples of water under examination, and compare immediately after
mixing. If 100 cc. of the sample is used the iron in parts per million
is equal to the number of cubic centimeters of the standard iron
solution in the standard that the sample matches.
_Second procedure._—For a small number of determinations it is more
convenient to run the standard iron solution into a Nessler tube
containing the acid, distilled water, and potassium sulfocyanide until
the color matches that of the sample tested. When determining iron in
three or four samples the colors may be matched in the order of their
intensity and the volumes of standard iron solution required for each
tube may be read from the burette.