CHECKING CONDUCTIVITY IN MULTI-ELECTROLYTE
SOLUTIONS
A conductimetry control often allows the chemical-physical variation of a
solution to be detected. In oceanography the total saline content may be
determined by means of conductivity measurements. In lake or river water
a variation in conductivity is often the sign of pollution due to industrial
waste water. The hardness of the feeding water for boilers, cooling towers,
steam generators, etc. may be determined approximately by means of
conductivity measurements. (In Italy it is sufficient to multiply the conducti-
vity at 20°C by 0.7 to obtain the quantity of equivalent salinity expressed in
ppm of CaCO
3
). In the food industry the concentration of various saline
solutions for preserving foodstuffs may be determined by measuring con-
ductivity.
SALINITY OF THE SOIL
It is a known fact that for different types of plants, flowers and cereals there
are optimum soil salinity values. Conductivity measuring allows indirect
determination of the salinity of the soil.
The method adopted by the Italian Society of Science of the Soil is the fol-
lowing:
Take a sample of soil, dry it in the air and riddle it at 2 mm. Dissolve it in 5
times its volume of demineralized water. Stir for about 30 minutes. Let the
liquid rest for a few minutes and take the measurement with an electrode
immersed in the liquid just over the soil sediment. The conductivity found
must be expressed in µS/cm at the temperature of 20°C. The salinity of the
soil is calculated with the formula:
where: S
= salinity of the soil in gr/100 of soil
20 = conductivity expressed in µS at 20°C
The measured values allow the regulation of the dose of fertilizer in the irri-
gation water.
ENGLISH
– 44 –
0.32 •
20
S =
1000
