Manual VISOCOLOR
2.5 Preparation of soil extract A
Soil extract A, which is prepared with extraction solution A (cal-
cium chloride solution, 0.0125 mol/dm
value, ammonium, nitrite and nitrate.
Preparation of the extraction solution:
Using the plastic syringe (12), transfer 10 mL of the CaCl
solution (28) into the bottle for extraction solution A (4) add 1 L of
distilled water (6) and mix.
2
4
6
CaCl
2
8
10
ml
12
28
Preparation of the soil extract:
Soil extract A is produced from the non-dried soil sample. The
soil sample should not be too wet and – if possible – it should
be screened. Remove all coarse and untypical constituents. In
a plastic beaker (17), weigh out 100 g of the soil sample, which
was prepared as described above. Add 100 mL of extraction so-
lution A (4). Stir vigorously with the metal spatula (5) for 2 min,
leave to stand for 15 min, while stirring again several times during
this period.
17
Place a funnel (7) on a 100 mL measuring cylinder (8), insert a
folded filter MN 616 ¼ (21). Pour the suspension into the folded
filter. If the filtrate is too cloudy at the beginning of filtration, pour it
back into the filter. With certain soils, slight coloration or clouding
is unavoidable. This will not affect the determinations described
below. Should it prove impossible to filter particularly problematic
soils due to high silt or clay content, we recommend the follow-
ing procedure: Pour the suspension into the measuring cylinder,
leave to stand for a prolonged period (e.g. overnight) and use
the clear or slightly turbid supernatant for analysis (remove with
syringe 10 mL, fitting the enclosed tube section (39) on the sy-
ringe (12) beforehand. Rinse syringe several times with water
afterwards).
24
®
reagent case for soil analysis
3
), is used to analyze pH
Destilliertes
A
Wasser
Distilled water
CaCl
Eau déstillée
2
Agua destilada
4
6
A
CaCl
2
4
5
7
ml 100
stock
2
90
80
8
70
60
50
40
30
20
9
10
2.6 Determination of the pH value
The pH value is determined in soil extract A using colorimetry or
pH indicator strips.
Procedure:
Insert the color disc pH 4.0–10.0 into the VISOCOLOR
comparator block (20). Fill both measuring glasses (19) up to the
6
ring mark with soil extract A and place them in the comparator
block (if the soil extract is colorless, the glass on the left can be
filled with clear water). Add 4 drops of pH 4–10 (36) to the right
glass, close and mix. Look through the glasses from above, com-
pare the colors of the two glasses and turn the color disc until the
colors match. Read off the result from the marking on the front
side of the comparator block. Intermediate values can be esti-
mated. After use, rinse both round glasses thoroughly and close.
pH 4–10
36
When pH values of less than 4.5 are measured, an additional
measurement is carried out with pH-Fix 2.0–9.0 test strips (26).
Manual VISOCOLOR
ml
17
12
MN 616 ¼
pH 4–10
19
®
reagent case for soil analysis 02.19
2
4
6
8
10
39
21
®
HE
20