Hach DR/700 Procedures Manual page 166

SILICA, HR,
4.
Fill a 10-mL cell
to the 10-mL line
with sample.
Note: A 25-mL sample
can be tested by using
25-mL sample cells and
optional reagents.
Note: For proof of
accuracy, use a 50 mg/L
Silica Standard Solution
(listed under Optional
Reagents) in place of
the sample.
Note: Sample
temperature should be
15 to 25°C (59 to 77°F).
10 minutes
7.
Wait 10 minutes.
continued
5.
Add the contents
of one Molybdate
Reagent Powder
Pillow For High
Range Silica. Cap
and invert to mix.
Remove cap.
8.
Add the contents
of one Citric Acid
Powder Pillow to the
sample cell (the
prepared sample).
Cap and invert to
mix.
Note: The yellow color
due to any phosphate
present will be removed.
42-82
6.
Add the contents
of one Acid Reagent
Powder Pillow For
High Range Silica.
Cap and invert to
mix.
Note: Silica or
phosphate will cause a
yellow color to develop.
2 minutes
9.
Wait 2 minutes.