This is an improvement on the author's method of two years ago. The
method is now applicable to compounds with which previously low
results were obtained.
The substance is weighed into a small tube 24 mm. long and 11 mm.
wide, and is then introduced into the decomposition flask, which
contains 6 to 8 grms. of chromic acid, care being taken that the
chromic acid does not come into contact with the substance under
analysis. The decomposition flask is fitted with a thistle funnel, and
is connected to the reversed condenser and apparatus shown in the
figure. Fifty c.c. of concentrated sulphuric acid are run into the
flask. During the whole of the operation a gentle current of air (free
from carbon dioxide) is passed through the apparatus. The asbestos
plate underneath the flask is then warmed, and thus the flask and
contents are warmed by radiant heat from the plate alone until the
sulphuric acid darkens. At this point, where decomposition of the
organic substance begins, the flame is entirely removed. The carbon
dioxide (with some carbon monoxide) passes through the condenser and
then over a heated mixture of copper oxide and lead chromate contained
in a tube 15 cm. long. The gas (CO2) then passes through a U-tube,
in one limb of which is sulphuric acid, in the other glacial
phosphoric acid.
[Illustration: APPARATUS FOR THE ESTIMATION OF CARBON IN ORGANIC
SUBSTANCES.]
Thus dried it passes through weighed potash bulbs, after which is
placed for safety a small tube containing soda lime and phosphoric
acid. After the lapse of about twenty minutes, warming may be once
more proceeded with in the same manner as before, and after about two
and one-half hours the asbestos plate may be placed directly below the
flask, and more strongly heated. The whole operation is very easily
carried out, and needs no watching.
With substances containing halogens, it is advisable to place, after
the copper oxide tube, a small washing flask containing potassium
iodide solution.
* * * * *