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MAKING A HAIR HYGROMETER - Level 1

Detecting moisture in the air

EXPERIMENT 15

Equipment:

Empty milk carton
Large sewing needle
Broom straw, 2" long
Scotch or masking tape
Penny
9" human hair, wiped clean of oil
4 thumbtacks
Paper clip
Dishpan

Cut the carton so as to make a small horizontal slit near the top; insert the paper clip. (Fig.1) Cut a vertical slit near the bottom. Then cut horizontal slits perpendicular to this cut at its end points - like an H on its side. (Fig.1)
Pry out the flaps thus made and bend them to an upright position. Insert the needle through these flaps. (Fig.2)
Tie the hair to the paper clip, wind it around the needle, tape the penny to the other end of the hair, and let the penny hang over the end of the box, which should be lying on its side.
Put a card with a scale on the side of the carton under the straw which has been pushed through the eye of the needle. (Fig.3)
Place the hygrometer on a wet towel in a dishpan and cover with a damp cloth. After 15 minutes remove it from the cloth and set the straw at numeral 10 on the scale. Watch to see whether the straw moves.
Since humid air causes the hair to stretch and dry air causes it to shrink, the straw should move toward the dry end of the scale as the hair dries.

Funded in part by

From
Raytheon Aviation
Educational Materials

Updated: February 23, 1999