Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

60 THE ABSOKPTION APPAEATUS
chromate dust. Then introduce successively a layer of silver wool
1-5 to 2 cm. long, a small loose asbestos pad, and finally a loose pad
of platinised asbestos 2-5 cm. long or a small roll of platinum-wire
gauze 3 cm. long. After five successive combustions of compounds
containing halogen or sulphur renew the last silver layer.
Test the permeability of the filling as described above and carry
out a final calibration of the bubble-counter. Burn out the whole
length of the tube whilst a current of dry air or oxygen is passing.
The tube is now ready for the combustion of nitrogen-free substances.
Such substances are preferably burned in a current of oxygen
instead of air.
For the combustion of substances containing nitrogen reduce the
5 cm. layer of copper oxide in a current of hydrogen in the manner
described under nitrogen determination. After the reduction burn
out the filling for half an hour in a gentle current of dry nitrogen,
allow to cool in nitrogen and then expel the nitrogen with air.
Repeat the reduction of the copper layer when necessary—at
the earliest after four determinations. If carefully handled the combustion
tube has a life of 100 analyses and more.
The Absorption Apparatus. Filling this Apparatus.—Small thinwalled
glass on tubes with two ground glass stoppers
(Blumer-Berger tubes, Fig. 38) are
used for absorbing the water and
carbon dioxide produced during the
combustion. The external diameters
of the small side tubes and the external
diameter of the constricted
part of the combustion tube must
all correspond exactly. One of the
ground stoppers of calcium chloride
tube serves as a "water trap"
having a fine hole in its inner end.
A capillary tube is sealed over this
hole.
Clean and dry the calcium chloride
tube and fill it as follows : First
slightly grease with vaseline the
FIG. 38
stopper with the capillary, keeping
clear of the upper two millimetres, or alternatively removing the
vaseline from this part with a cloth—in this way the expression of