Geoscience Reference
In-Depth Information
Introduction of
carbon dioxide
if necessary
Condensation
Atmospheric
zone
Rain
S
Residue from
weathering
R
Phreatic
zone
E
Drainage
Evaporation
Accumulation
of leachate
Heat source
Fig. 1.9
The Soxhlet apparatus used by Pédro (1964).
The limitations of the apparatus are of two kinds, as reported in
work by students of Pédro: (i) when the experiments are continued over
a long period, there is risk of green algae developing especially if the
work is done at low temperature; it is then advisable to eliminate light
and to sterilize the assembly; (ii) silica being soluble, the glass of the
Soxhlet could contribute some of it to the extract.
1.3 DATING AND TRACING
1.3.1 Generalities
The chemical elements contain definite numbers of protons, electrons
and neutrons. Two atoms that differ in their number of neutrons may
have different atomic masses but retain the same general chemical
properties. They have the same atomic number. They are
isotopes
(e.g.
14
C and
12
C). Two atoms that have the same atomic mass but different
number of neutrons and protons have electrons in different amounts and
therefore have different chemical properties. They are different bodies
(e.g.
40
K and
40
Ar). They have different atomic numbers.
In soil science, isotopes are used in two ways as discussed below.
