DETERMINATION OP MOLECULAR WEIGHT 35Split Cork- Wire Holder
of the wire holder to a ring stand. A split cork stopper will hold
the wire in the jaws of the clamp. The bottom of the bulb should
be about 1 cm. from the bottom of the beaker. Carry the apparatus
to the hood, and heat the water
with a low flame until it reaches
the boiling point. Maintain the K
bath at this temperature until
the carbon tetrachloride has en-
tirely vaporized, and the excess
vapor has escaped through the
open tip. After a lighted match
is no longer extinguished at the
tip, wait two minutes for the
vapor in the bulb to be heated
to the temperature of the boiling
water, and for the pressure in-
side the bulb to come to equilib-
rium with the atmosphere out-
side. Still keep the water
boiling, and, by means of a
second burner, warm the ex-
posed stem to vaporize any car-
bon tetrachloride which may
have condensed in it. Seal the
bulb by holding the flame at
the tip of the capillary. Re-
move the bulb from the beaker,
dry it, and tip it bottom up.
The condensed carbon tetra-
chloride will run into the stem
of the bulb, and if the tip is not
completely sealed bubbles of air
.Dumas BulbUnglazed
/ Porcelainwill be drawn through the liquid - d
into the bulb. If this happens FIG- 13
turn the bulb right side up and
immediately reheat the tip. If the seal is satisfactory allow the
bulb to cool to room temperature and weigh it accurately.
After the sealed bulb has been weighed it is to be filled with
water and weighed on the platform (not the analytical) balance.
Water from which dissolved air has been expelled must be used