MXMF.Users.Handbook.V2.20.doc
LIT:MXUHB April 2003
3
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A.
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Basic Measurement & Performance Q&A
1. What is moisture content
?
Moisture content is usually shown as a percentage of water contained in a solid, liquid or vapor material.
Where sample is vapor or liquid, it can be in percentage of weight of water contained in its sample’s
volume and it can be called hygroscopic moisture or humidity. Since moisture content may be classified
into various statuses with names to them, evaluation of and dealing with measured data require a special
care.
Moisture adhered to a material’s surface is called water of adhesion, free water or hygroscopic moisture
and moisture adhered to a material with a certain condition such as pressure, temperature, volume etc. is
called absorbed water or equilibrium moisture content. Water chemically bonded to a material itself or
inside of the material is crystal water or hydrated water while its moisture is bond water or combined water.
REFERENCE
In measurement of moisture content with a moisture analyzer, some materials are measured with a stable
moisture content rate and a typical material with such character is Sodium Tartrate Dihydrate. Known by its
name, it is a well-known material secondarily produced while alcoholic beverages such as wine is made.
The material is a hydrate that has hydrate water in crystal and a combined material
(
molecular formula :
Na
2
C
4
H
4
O
6
?
2H
2
O, rational formula [H
2
O
?
CH(OH)COONa]
2
/ molecular mass 230.0823
)
of Sodium
Tartrate
(
molecular formula : Na
2
C
4
H
4
O
6
?
rational formula [
-
CH(OH)COONa]
2
/ molecular mass
194.0517
)
and two water molecules
(
2H
2
O
?
molecular mass 36.03056
)
. Sodium Tartrate Dihydrate
changes into Sodium Tartrate (anhydrate) by releasing the two water molecules with heat energy. Since
Sodium Tartrate Dihydrate’s melting point is 150
?
, at room temperature it is stable and does not release
crystal water in its molecules but starts releasing the decomposition of other factors than crystal water.
Thus, in order to vaporize crystal water selectively when moisture is measured with a moisture analyzer
using heating and drying method, it is suffice to say that heating temperature should be between 150
?
to
200
?
.
Its moisture content rate is logically deemed by the ratio of 2 water molecules, that is (36.03056/
230.0823)
×
100
?
15.66%.