(^32) QUANTITATIVE ASPECTS OF CHEMISTRY
should be prepared with especial care and be weighed accurately-
just before starting the operation. Prolong its open arm with an
elbow tube whose one end, drawn out to a capillary, is turned
upward. Test the tightness of the apparatus: This may be done
by adding enough water to the generating bottle to seal the end
/Ring
•Comirasflbn Tube
Porcelain Boat and CuO
- Ring Stand^
Cotton
[am Chloride
Side Arm U-TobeFIG. 12of the thistle tube, then holding a finger on the exit tube of the
apparatus and pouring more water into the thistle tube. If the
top of the column of water in the thistle tube maintains its level
the apparatus is tight. Pour a few cubic centimeters of 6iV
hydrochloric acid through the thistle tube, let hydrogen generate
slowly, and fill the apparatus while preparing the rest of the
material.
After it has cooled, accurately weigh the porcelain boat filled
with the copper oxide. Place the boat carefully, without spilling
any of the copper oxide, in the middle of the combustion tube.
Add a little more acid to the generator, and wait until the ap-
paratus is completely rilled with hydrogen before proceeding fur-
ther. Never bring a flame near the apparatus until the purity of
the hydrogen escaping has been proved. Test the hydrogen by
holding a short test tube over the jet and carrying the tube, mouth
downward, to a distant flame. If the gas does not explode, but
burns quietly, quickly convey the tube, still with mouth down-
ward, to the jet. If the hydrogen still burning in the tube ignites
the jet, it is then safe to proceed with the experiment. The gas
at the jet should be left burning. Increase the evolution of hydro-