7. Die sechs Stoffe aus Versuch
1 trocknen (Gravimetrisch)
(Seite im Aufbau)
Washed fabrics will dry at temperatures
below zero. The direct transformation of ice (solid water) into water vapour
is industrially used to produce instant coffee: In a first step brewed
coffee is deep frozen, then in a vacuum chamber at a temperature of micus
70° the ice directly changes into water vapour.
You will do a freeze drying at normal air pressure.
This will take time. Nevertheless you will achieve the direct transformation
of frozen water from the fabric to vapour by repeating Experiment 5 in a deep-freeze.
To find out how fast this low-cost freeze
drying works, balance the frozen fabric on the scale, return it
into the deep-freeze and reweigh every six or twelve hours until the fabric
is dry again.
.
.
Materials
like in experiment 3, deep-freeze.
Experiment
like in experiment 3. Between two
weighings keep everything (including the scale) in the deep-freeze.
Observations
1. After 6 hours in the deep-freeze
(Fig. 1) the fabric has clearly lost weight (Fig. 2).
2. After one week the frozen water
in the fabric has been reduced from 2 g (mL) 0.4 g.
Explanation
Der Vorgang, durch den Eis (festes
Wasser) direkt gasförmig wird, heißt Sublimation.
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Veränderung: 22.02.2006