PRINCIPLE OF SEPARATION
In a liquid with density d particles with density >d will sink and particles with density ???
A mixture of the particles to be separated as well as diiodomethane are put into a turning conical cup. Particles heavier than the liquid (here marked with dark spots) will be flung to the outer part and thus will stay in the cup. Particles lighter than the liquid will be flung, with the overmeasure of diiomethane, out and collected via the overflow (1 and 2) in a beaker (7).
- Heavy liquid: diiodomethane d=3.12 en d=3.30
- Cleaning liquid: acetone
- Various stainless steel containers
- Small brush
- Stainless steel beakers
Different funnels which, dependent on grain size, can be used. See the schedule on the back wall. Determine the number of revolutions. Turn on the centrifuge (under the work top) and set the number of revolutions. Place a paper filter in both filter units with a beaker under them. Check exhaust by laying a hand on the unit and pressing the switch for the filter unit (at the front under the work top) on "open". Repeat this for both filter units. The left one is only for the heavy liquid and the right one is for washing with acetone. Check the liquid density with a density gauge. A small sample (not more than about 10cc) can be placed in the beaker directly. Then heavy liquid is added (see figure) and well stirred, after which the beaker is placed in the centrifuge. Larger samples are mixed in a different beaker with heavy liquid (proportion 40/60) and fed into the funnel in the rotating centrifuge. After the entire sample has been fed into the centrifuge, thorough rinsing with heavy liquid must follow. Take care that the beaker does not overflow at the outlet. As soon as no grains appear from the outlet the centrifuge can be switched off. Both float and sink are to be filtered first through the left filter unit to regain the heavy liquid. Then they have to be cleaned with cleaning liquid on the right filter unit (no acetone must be used on the left filter unit!), and dried, after which the fractions must be collected in a stainless steel bowl. Write on it 'sink 3.12' or 'float 3 …' etc.
After each separation all parts of the centrifuge must be rinsed thoroughly with aceton, so as to avoid contamination with following samples. Collect the cleaning liquid in one cup and use this to clean the float.
All parts of the centrifuge, as well as the work top have to be cleaned very well. Switch off the vacuum pump and turn air exhaust on 'LAAG' (low).