_Reagents._—Platinum solution. Dissolve 2.00 grams of potassium platinic
chloride (PtCl_{4}.2KCl) in a small amount of distilled water, add 100
cc. of strong hydrochloric acid, and dilute to 1 liter.
Cobalt solution. Dissolve 12 grams of cobaltous chloride
(CoCl_{2}.6H_{2}O) in distilled water, add 100 cc. of strong
hydrochloric acid, and dilute to 1 liter.
Prepare standards by putting various amounts of these two solutions into
Nessler tubes and diluting to the 50 cc. mark with distilled water as
indicated in Table 5. These standards may be kept for several months if
protected from dust.
Table 5.—PREPARATION OF PERMANENT STANDARDS FOR THE DETERMINATION OF
AMMONIA.
───────────────────────┬───────────────────────┬───────────────────────
Value in standard │ Solution of platinum. │ Solution of cobalt.
ammonium chloride. │ │
───────────────────────┼───────────────────────┼───────────────────────
_cc._│ _cc._│ _cc._
0.0│ 1.2│ 0.0
.1│ 1.8│ .0
.2│ 2.8│ .0
.4│ 4.7│ .1
.7│ 5.9│ .2
│ │
1.0│ 7.7│ .5
1.4│ 9.9│ 1.1
1.7│ 11.4│ 1.7
2.0│ 12.7│ 2.2
2.5│ 15.0│ 3.3
│ │
3.0│ 17.3│ 4.5
3.5│ 19.0│ 5.7
4.0│ 19.7│ 7.1
4.5│ 19.9│ 8.7
5.0│ 20.0│ 10.4
│ │
6.0│ 20.0│ 15.0
7.0│ 20.0│ 22.0
───────────────────────┴───────────────────────┴───────────────────────
The amounts in Table 5 are approximate, and the actual amount necessary
will differ with the character of the Nessler solution, the color
sensitiveness of the analyst’s eye, and other conditions. The final test
of the standard is best obtained by comparing it with Nesslerized
standards and modifying the tint accordingly. Such comparison should be
made for each new batch of Nessler solution and should be checked by
each analyst.
_Procedure._—In comparison with permanent standards, Nesslerize the
distillates in the manner above described and compare the resulting
colors at the end of about 10 minutes with the permanent standards. The
method of calculating results is precisely the same as with the ammonia
standards.