Paul Zane, age 12, of Longview, Wash., for his question:

WHAT MAKES A VACUUM BOTTLE?

A vacuum bottle is actually two bottles in one. The bottle, also sometimes called a Thermos bottle, can keep liquids cold or hot for as long as a day.

The vacuum bottle has an inner container which is made of glass. This inner container is the bottle within a bottle. It is sealed at the lips by melting the glass edges. Air is removed from the space between the two bottles to produce a near vacuum.

Glass is a poor conductor of heat but a vacuum conducts heat even less. The vacuum between the bottles slows down the transfer of heat by convection. To reduce the transfer of heat by radiation, the facing surface of the glass bottles are coated with a silvery solution of aluminum which reflects heat.

Cork is used for the stopper and for the pads which hold the bottles within their outer container because cork is a poor conductor of heat. The outer container is made of metal or of molded plastic. The bottles are held in place within the container by a rubber collar at the top of the container. A spring at the bottom of the bottle acts as a shock absorber.

The first vacuum bottle was the Dewar flask invented in 1885 by Sir James Dewar as a way of keeping heat away from liquid gases with which he was experimenting.