O is held by many substances so tenaciously that we can not liberate it; this gives us “terra firma.” Sand, and many rocks consist of O and silicon, but the greatest heat and heaviest blows can not separate them. There are materials, however, which readily yield their O. Dr. Priestly first found it by heating with a burning glass a compound known now as red oxide of mercury. The O went off, leaving the shining quicksilver.
You may repeat this historic experiment by placing the material in a test tube and heating it over an alcohol lamp.
Another substance used for this purpose is black oxide of manganese (MnO₂), but that which is now generally employed is a white salt, kept by every druggist, and usually called chlorate of potash (HClO₃).
PREPARATION OF OXYGEN FROM A MIXTURE OF POTASSIC CHLORATE (CHLORATE OF POTASH) AND MANGANESE DI-OXIDE.
Place a small amount of this, mixed with an equal quantity of the manganese, in a test tube, or flask, and heat over a flame. The O will be liberated, and may be bottled for use. A strange thing about this operation is that the MnO₂ yields none of the O, but comes out of the flask just as it went in. Such action, by mere presence, is called catalysis. We can not explain it, but have some such phenomena in social life, perhaps, when two people with an affinity for each other are having a delightful, confidential chat, and a third person joins the group, immediately producing silence—a plain case of catalysis! Having secured several jars of O we are now ready to test some of its interesting properties. Extinguish a candle and suddenly plunge it into a jar of O. It is relighted. A better way is to make a taper of waxed thread. This will keep the live coal better, and may be relighted many times. Attach to a wire a piece of charcoal bark. Ignite and place in another jar. Beautiful scintillations fill the jar, star like in form. Take a watch spring, heat one end and bend. Split a match and attach to the spring, light and place in the jar. It burns with great brilliancy.
Whittle out a little cup of chalk, or crayon, and place phosphorus in it. Touch the P with a hot wire and lower the cup, with a wire, into a jar of O. A beautiful combustion follows. In like manner sulphur may be burned, and produces a bright blue light.
A TAPER OR CANDLE BURNING IN OXYGEN.