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Teil 3 Seite 6-16
Liming is usually done in large concrete pits that can contain the ossein from one batch
of demineralised bone chips. The ossein is submerged in a solution of supersaturated
lime to purify and condition the collagen to promote its hydrolysis. The pH during this
process is approximately 12.5, i.e., the pH of fresh made lime solution. The supersatu-
rated lime solution is refreshed regularly to compensate for consumption during the proc-
ess. Air is blown through regularly, to prevent the pH becoming locally too low.
After the last decanting of the lime the ossein is washed by filling the lime pit with about
the same amount of water as the weight of the original bone chips and leaving it in for
some time before running it off. The ossein is then washed a second time by agitating it
with about the same amount of water, after which it is pumped in a stream of water to the
neutralisation installation. The washings contain lime and can be used to neutralise the
acid used in the early process, otherwise caustic soda would be required.
A typical liming process schedule is shown in Table 6-1, the number of days varies be-
tween installations and can be as high as 90, depending on quality of the bone chips, the
average temperature of the lime and the desired physical properties of the gelatine. The
frequency of refreshing the lime, the frequency and the time of blowing air into the pit and
the number of times the ossein is washed, with or without agitation, also varies between
installations and batches.
Table 6-1 Typical liming process schedule
Day Adding fresh
lime
1 X
Decant-
ing
2 X X
Pump-
ing air
3 X
4 X X
8 X
9 X X
12 X
15 X
17 X X
21 X
25 X
27 X X
31 X
35 X
Wash-
ing