[Illustration: FIG. 22.--Preparing oxygen from potassium chlorate and
manganese dioxide.]
36. How to Prepare Oxygen. Mix a small quantity of potassium
chlorate with an equal amount of manganese dioxide and place the
mixture in a strong test tube. Close the mouth of the tube with a
one-hole rubber stopper in which is fitted a long, narrow tube, and
clamp the test tube to an iron support, as shown in Figure 22. Fill
the trough with water until the shelf is just covered and allow the
end of the delivery tube to rest just beneath the hole in the shelf.
Fill a medium-sized bottle with water, cover it with a glass plate,
invert the bottle in the trough, and then remove the glass plate. Heat
the test tube very gently, and when gas bubbles out of the tube, slip
the bottle over the opening in the shelf, so that the tube runs into
the bottle. The gas will force out the water and will finally fill the
bottle. When all the water has been forced out, slip the glass plate
under the mouth of the bottle and remove the bottle from the trough.
The gas in the bottle is oxygen.
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