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. [Illustration: A TAPER OR CANDLE BURNING IN OXYGEN.] A little ingenuity will supply all apparatus needed for these and other experiments with H and O. For example, a common pail with a wooden shelf in it two or three inches from the top makes an excellent pneumatic trough for transferring or gathering gases, and if the shelf can not be procured, two or three bricks in the pail will serve the purpose. Before dismissing our glass of water we must remark that no matter where it may be found, in the depths of the sea or on the mountain; as a dew drop, or sparkling as spray; in lake Nyanza, or lake Chautauqua, the chemical constituents of water are just the same. Almighty care and wisdom weighs the atoms, even as “he weighs the mountains in scales and the hills in a balance.” The _apparent_ character of water, as to color, form, hardness, saltness, and so on, is often varied by _mixing_ with it other substances, but the changes produced are not chemical, and belong more properly to the domain of physics. NOTE.—The illustrations in this article are from “The Young Chemist” of Prof. John Howard Appleton. We can heartily recommend to the members of the C. L. S. C., all of Prof. Appleton’s admirable works on Chemistry. STUDIES IN KITCHEN SCIENCE AND ART. I. THE POTATO. BY BYRON D. HALSTED.