Chromatography

  This is a classic crime scene mystery solved in classrooms. You could have teachers with different black pens and the students have to find out who wrote the note. A particular pen could be found in the pocket of a suspect.

     I use white school fan fold paper towels instead of the coffee filters. They absorb the water quickly and also dry quickly. You can also use coffee filters or filter paper. The better quality paper towels take longer to absorb the water.

MATERIALS:

     washable black felt tip markers
     paper towels (school white fan fold)
     water
     plastic cup
     paper towel with message or phone number in black
     washable felt tip marker

ADVANCED PREPARATION:

     Write a message or phone number on a piece of paper towel. Cut the pieces of paper towel into strips. Label the washable black felt tip markers with the names of the suspects.

PROCEDURE:

1. Cut a piece of the paper towel left at the crime scene. In front of the class dip
   the tip of the paper towel (Do not get the part with the marker in the water.) in
   the water. Let the water run up the paper towel. You will see the colors separate.

2. Draw a line on the coffee filter with one of the pens. Identify the pen on the
    strip.

3. Dip the tip of the coffee filter strip in the water. Make sure that the marker line
    does not touch the water in the cup.

4. Let the strip dry.

5. Repeat with each of the other pens.

6. Match your strips to the chromatography of the note written by the criminal.