Carnegie Mellon University

Who Wrote the Note: Procedure

  1. Use a pencil to trace a circle in the center of a piece of filter paper.  With the pencil, write the numbers 1, 2, and 3 inside the circle as shown below.
  2. Just above the circle, beside the number 1, make a pin-head size dot with pen 1 by lightly touching the paper with the pen tip. Use pen 2 to make a dot by the number 2, and pen 3 to make a dot by the number 3, as shown in Figure 1.
  3. wrote-note1

    Figure 1

  4. Roll up a small triangle of filter paper to be used as a wick.  Poke a small hole in the center of the circle on the filter paper with a pencil and insert the wick through the hole as shown in Figure 2.
  5. wrote-note2

    Figure 2

  6. Fill the dish 1/3 full with water and carefully lay the filter paper on top of the dish so that the wick is in the water as shown in Figure 2. The flat end of the wick should be resting on the bottom of the dish.
  7. Wait 10 minutes for the chromatogram to develop or until the water is about 1 inch from the paper's edge.  While waiting, prepare the ransom note for analysis.
  8. wrote-note3

    Figure 3

  9. Cut a portion of the signature section from the note, leaving as much blank paper as possible.  Suggested ways to cut are shown below.
  10. wrote-note4wrote-note5

    Figures 4 and 5

  11. Use a strip of plastic as a brace to support the portion of the note and use a triangle of filter paper for a wick as before. Stand the wick up against the brace and then position the ransom note portion so that it is touching the wick. See Figure 6.  Lean the wick against the edge of the ransom note portion and do not allow the ransom note portion to come into direct contact with the water.


    Figure 6

  12. Wait 10 minutes (or until the water is 1/2 inch from the edge of the ransom note paper.
  13. Compare the colors and their positions on the chromatogram of the ransom note with those of the three pens.  Which pen matches the one that signed the note?
See the "Who Wrote the Note" data sheet [.pdf].


Empty and dry the plastic dish.  Return the dish, pens and other equipment to the teacher.  You may keep the chromatograms. Allow them to dry completely.