MLB50-3-BA-defsi-0310
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7 Moisture determination
7.1 Use
The rapid determination of moisture content is of enormous significance wherever
moisture has to be added to or removed from a product during manufacture. For in-
numerable products, the moisture content is both a measure of quality and also an
important cost factor. When trading in industrial or agricultural products, as well as in
products in the chemical or foodstuffs field, firm limits for moisture content, defined by
sales agreements and standards, often apply.
7.2 Sample material
Samples with the following properties can usually be determined satisfactorily:
♦ Granular or powdery, floatable solids.
♦ thermally stable materials, which readily give off the moisture to be determined
without volatilising other constituents.
♦ Liquids, which evaporate to dryness without forming a skin.
The determination can be difficult in samples which:
♦ are viscous/sticky liquids.
♦ tend to form a crust or skin readily on drying.
♦ tend to decompose easily or liberate different constituents on heating.
7.3 Sample preparation
Special preparation of the samples is, in many cases, not required. Large solid bod-
ies, e.g. kernels and grains, should, however, be ground. Both the drying time and
the accuracy which can be achieved will be greatly influenced by the sample distribu-
tion. The result is that there are two contradictory requirements:
The lighter the load being weighed, the shorter the drying times which can be
achieved and the heavier the load, the more accurate will be the result.
Sample distribution:
Solid material
Distribute powdered and granular samples evenly over
the balance pan. Reduce the size of coarse samples
(grind, mortar)
Liquids
Apply tough and sticky products thinly. the use of circular
glass-fibre filters or quartz-sand is recommended.
Weight loss through spattering can be prevented by
covering the sample with a circular glass fibre filter. If
circular glass-fibre filters or quartz-sand are used the
weight must be subtract by tarring.
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