Even carbon dioxide can dissolve in the groundwater, causing the water to be naturally carbonated. This water is sometimes sold as mineral water. Groundwater can be heated by magma below the Earth's surface. The heated water can create hot springs, springs with water that is naturally hot (Figure 13.23). Some hot springs are used as natural hot tubs and are considered therapeutic and spiritual by some people. However, hot springs can be dangerous, too.
We used a level tablespoon of salt in a cup of water. The batteries we have shown here are more correctly called cells. An actual battery is made up of two or more cells. The zinc-air cell produces about three quarters of a volt.
1 Alkaline battery: This chemistry is also common in AA, C and D dry cell batteries. 2  The cathode is composed of a manganese dioxide mixture, while the anode is a zinc powder. 3  It gets its name from the potassium hydroxide electrolyte, which is an alkaline substance. Zinc-carbon battery: The zinc-carbon chemistry is common in many inexpensive AAA, AA, C and D dry cell batteries. 2  The anode is zinc, the cathode is manganese dioxide, and the electrolyte is ammonium chloride or zinc chloride. 3  Alkaline battery: This chemistry is also common in AA, C and D dry cell batteries.