_Reagents._—1. Platinum solution. Dissolve 2 grams of potassium platinic
chloride (PtCl_{4}.2KCl) in distilled water, add 100 cc. of concentrated
hydrochloric acid, and dilute to 1 liter with distilled water.
2. Cobalt solution. Dissolve 24 grams of dry cobaltous chloride crystals
(CoCl_{2}.6H_{2}O) in a small amount of distilled water, add 100 cc. of
strong hydrochloric acid, and dilute to 1 liter with distilled water.
_Procedure._—Prepare a series of permanent standards by diluting to 50
cc. with distilled water the amounts of platinum and cobalt solutions,
in 50 cc. Nessler tubes, indicated in Table 9. Compare the sample with
these standards, and calculate the parts per million of iron.
Table 9.—PREPARATION OF PERMANENT STANDARDS FOR THE DETERMINATION OF
IRON.
───────────────────────┬───────────────────────┬───────────────────────
Value in standard iron │ Platinum solution. │ Cobalt solution.
solution. │ │
───────────────────────┼───────────────────────┼───────────────────────
_cc._ │ _cc._ │ _cc._
0.0│ 0│ 0.0
.1│ 2│ 1.0
.3│ 6│ 3.0
.5│ 10│ 5.0
.7│ 14│ 7.5
1.0│ 20│ 11.0
1.5│ 28│ 17.0
2.0│ 35│ 24.0
2.5│ 39│ 32.0
3.0│ 39│ 43.0
3.5│ 40│ 55.0
───────────────────────┴───────────────────────┴───────────────────────