If water were like most liquids, the bottoms of all the oceans and even the entire body of water in most cases would be permanently frozen. Again, as a solvent there is literally nothing to compare with water. As Henderson[6] puts it: "Nearly the whole science of chemistry has been built up around water and aqueous solution." One of the most significant evidences of this is the variety of elements whose presence can be detected in sea water. According to Henderson they include hydrogen, oxygen, nitrogen, carbon, chlorine, sodium, magnesium, sulphur, phosphorus, which are easily detected; and also arsenic, caesium, gold, lithium, rubidium, barium, lead, boron, fluorine, iron, iodine, bromine, potassium, cobalt, copper, manganese, nickel, silver, silicon, zinc, aluminium, calcium, and strontium. Yet in spite of its marvelous power of solution, water is chemically rather inert and relatively stable. It dissolves all these elements and thousands of their compounds, but still remains water and can easily be separated and purified. Another unique property of water is its power of ionizing dissolved substances, a property which makes it possible to produce electric currents in batteries. This leads to an almost infinite array of electro-chemical reactions which play an almost dominant role in the processes of life. Finally, no common liquid except mercury equals water in its power of capillarity. This fact is of enormous moment in biology, most obviously in respect to the soil. Although carbon dioxide is far less familiar than water, it is almost as important. "These two simple substances," says Henderson, "are the common source of every one of the complicated substances which are produced by living beings, and they are the common end products of the wearing away of all the constituents of protoplasm, and of the destruction of those materials which yield energy to the body." One of the remarkable physical properties of carbon dioxide is its degree of solubility in water. This quality varies enormously in different substances. For example, at ordinary pressures and temperatures, water can absorb only about 5 per cent of its own volume of oxygen, while it can take up about 1300 times its own volume of ammonia. Now for carbon dioxide, unlike most gases, the volume that can be absorbed by water is nearly the same as the volume of the water. The volumes vary, however, according to temperature, being absolutely the same at a temperature of about 15 deg.C. or 59 deg.F., which is close to the ideal temperature for man's physical health and practically the same as the mean temperature of the earth's surface when all seasons are averaged together. "Hence, when water is in contact with air, and equilibrium has been established, the amount of free carbonic acid in a given volume of water is almost exactly equal to the amount in the adjacent air. Unlike oxygen, hydrogen, and nitrogen, carbonic acid enters water freely; unlike