Roger Sobczak, abed 9, of Milwaukee, Wisconsin for his question:

How is rust formed?

An outdoor bar‑b‑que is good for a lot of fun. The stove and chimney are built of stones and mortar or bricks and mortar. An iron grill rests over the first hole. The bricks and stones can take care of themselves outdoors. But the iron grill must be specially made for outdoor living. Otherwise it will rust in the air and weather.

Naturally you need a poker to stoke the coals when you use the outdoor fireplace. Chances are, you will borrow the iron poker from the living room. If you forget to bring that poker back indoors, it will rust.

Suppose you leave it on the damp ground overnight. By morning it shows traces of orange rust. You can scour off this rusty dust. But tiny fragments of the iron have been lost with it.

Now suppose you left this indoor poker outdoors all winter, By spring you would hardly recognize it. Its hard surface would be chewed into flakes. The rust has broken up larger fragments of the iron. The metal is being eaten away bit by bit. In time it would all crumble away. The name for this rust decay is corrosion. Corrosion means gnawed away.

Is this chewing up done by minute creatures? Is the rust that devours an iron poker the same rust that devours a tree? The answer ig no to both questions. Tree rust is a tiny living plant and feeds on other plants. It is named because it looks like iron rust. Also, like iron rust, it destroys.

Iron rust is a chemical action. No living creatures take part in it. Certain atoms act in a certain way when they meet certain other atoms. That is, they set if conditions are dust right, The busiest atoms are atoms of oxygen. Atoms of oxygen rush into action whenever they get the chance.

Each atom of oxygen has two free arms with which to grab and pull. These arms are particles called electrons. When conditions are just right they grab iron atoms of iron to form particles of rust. The rust is a new substance which falls away from the solid iron in dust and flakes.

The right conditions for turning iron to rust need oxygen plus moisture. Oxygen is always present in the air. But it cannot react on the iron poker in the living room because there is not enough moisture present. If it is kept dry, such a poker will last a lifetime ‑ even in the air which contains oxygen.

But tons of iron must lead an outdoor life. Iron is used to build bridges, locomotives, railroad tracks. It is even used to make water pipes. Such outdoor iron and steel is sealed from the weather. Some times it is safe with a simple coat of paint or lacquer. Sometimes it is coated with a metal that does not rust so easily. Zinc, tin and lead are the metals most often used to coat outdoor iron. Chances are your outdoor barbeque is coated with chromium. Otherwise it would flake away in rust like the poker made of plain iron.