Robert Jackson, age 12, of Rochester, New York, for his question:

What are the exact ingredients in water?

This precise type of question is likely to spring from the mind of a budding scientist. A gifted young researcher has to probe to the very root of a problem. Others may be content to accept water as a compound of hydrogen and oxygen, but he needs the precise recipe.

Water is the world's greatest solvent. More substances dissolve in it than in any ofhet'"oonraon liquid and for this reason, strictly pure water is hard to find. We cant however, take today's precise question to mean the ingredients in pure water with absolutely no other dissolved ingredients. This survey must take us to the laboratory, for no perfectly pure water exists in nature. There are several ways to break it apart into its separate ingredients. These fascinating chores will yield the answer we need and also a lot of other related data.

Water, of course, is a mineral compound of the elements hydrogen and oxygen. Its chemical formula is H20, which tells us that its basic particle is a molecule of two atoms of hydrogen and one of oxygen. But if you suspect that the hydrogen in the compound is twice the weight of the oxygen, you would be wrong. It does, however, occupy twice the volume of the oxygen.

We could create a basic sample by distillins? impure water. The molecules in a flask of boiling water use heat energy to break their bonds andv speed off as separate particles of pas. The dissolved impurities are left behind arid the steamy vapor is led through a cooled condensing tube. The condensed droplets are caught in the flask and the whole apparatus is sterile to keep the sample pure. The purified colorless liquid has no smell or taste.

We also could form a supply of water from a mixture o£ gaseous hydrogen and oxygen ingredients. The energy for this chemical reaction may be an electric spark, or radioactive bombardment. More than 68,000 calories of energy are needed to start it. But the chemical reaction then yields lots of energy of its own. Once started, the energy released by the combination of hydrogen and oxygen helps to keep the process going. Delicate weight measuring reveals that the formation of water requires one

part of the hydrogen ingredient to exactly 7.94 parts of oxypen. Rounhly, eight weight units of oxygen combine with one unit of hydrogen to form nine units of water.

We can separate a sample of water into its gaseous ingredients and measure them by volume. This can be done by electrolysis. Water is a poor conductor, so we add a trace of sulphuric acid to make a faster acting solution. Two electrodes are placed in the bath and a current sent through the liquid. This makes the water molecules split into atoms of pas. Oxygen collects in an up ended flask above the positive anode. Hydrogen rises into a flask above the negative cathode. The experiment produces two flasks of hydrogen for one of oxygen. The volume of hydrogen is double the volume of oxygen.