Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

THE ABSOKPTION APPAEATUS 61
grease when the stopper is introduced is avoided. The ground
joint should be just transparent and the stopper should turn only
with considerable stiffness. Carefully remove excess of vaseline
from the opening in the stopper and from the side tube with a roll of
cotton wool. Now lay a small pad of cotton wool on the lower
stopper, pour in first a 1 cm. layer of coarsely granulated calcium
chloride, fix this layer in position with small pad of cotton wool and
then, with gentle sidewards tapping, pour in granulated calcium
chloride (granules the size of millet grains) previously dried at
180°-200° until the layer reaches to just below the upper stopper.
After this layer has been fixed in position with a dried pad of cotton
wool, insert the upper stopper first greasing it with vaseline as above
and carefully wiping away excess vaseline. Loosely fill the hollow
of the stopper with dry cotton wool.
Since the calcium chloride contains basic constituents the filling
must be saturated with carbon dioxide before the absorption tube is
used. For this purpose connect the side tube which leads to the water
trap to the Kipp apparatus, interposing a drying tube, pass a strong
current of carbon dioxide for 10 minutes, close the outlet, and allow to
stand for half an hour, maintaining the pressure of the Kipp. After
200 c.c. of dry air have been drawn through the tube by means of the
aspirator, the tube is ready for use.
One filling suffices for at least fifteen analyses. It is preferable
to renew the filling when that of the sodium hydroxide-asbestos tube
is being renewed.
Clean and dry the sodium hydroxide-asbestos tube and fill it as
follows. Push a loose pad of cotton wool into the hollow of the
lower stopper, suitably grease this and insert it. Lay another small
pad on the lower stopper and then pour in, with gentle sidewards
tapping, Merck's sodium hydroxide-asbestos until the tube is twothirds
full. Now fix this layer in position with a small pad of cotton
wool and introduce a layer 0-5 cm. deep, of ordinary not specially
dried calcium chloride. Again fix in position with a loose pad of
cotton wool and fill to just below the stopper with dried calcium
chloride (granules the size of millet grains) dried at 180°-200°.
Grease the upper stopper with vaseline and insert it after pushing in
another dried pad of cotton wool. The tube is now ready for immediate
use. The filling suffices for at least fifteen determinations.
As the sodium hydroxide-asbestos absorbs carbon dioxide the dirty
grey colour of the absorbent becomes noticeably lighter and observa-