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Let's make a spectroscope. Cut a circle of black paper to fit the end of a cardboard tube. Cut the circle in half. Tape one half onto one end of the tube and the other half beside the first, leaving a narrow slit between the two halves of black paper.

Your teacher will need to go the scientific supply house and purchase some diffraction grating. This stuff has parallel lines on it (15,000 to 30,000 per inch) that cause the light passing between them to spread out into a band of colors (the spectrum).

Hold a piece of diffraction grating up to the open end of your tube, and look through it at the opposite end of the tube and toward an electric light. Slowly rotate the grating until a bright color band is seen on one side of the slit; then tape the grating in place.

Now look through the instrument at a lighted fluorescent tube. You will see a spectrum on either side of the slit and can notice narrow bright lines in the yellow, green, or blue portions of the spectrum. The lines are caused by the glowing gases in the fluorescent tube.

Every element produces its own characteristic spectrum lines when it is heated to a point where it glows.

The instrument they have made is called a spectroscope.
Astronomers can look through a spectroscope at any glowing
body in space. By comparing the color patterns of known
elements with the spectrum of a star, they can determine what elements are present in the star.

Now hold a looped paperclip in a flame to clean it, wet the
loop slightly, dip it into chalk dust, and hold it in the flame again while examining the glow through the spectro- scope. You will see the spectrum that is characteristic of calcium.

Similarly, test baking soda (you will see the spectrum that
is characteristic of sodium) and other materials.


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