398 DIY Science: Illustrated Guide to Home Chemistry Experiments
PRTIII:A LR SI vE NITRATE SpRAy oALIpToN ACTIvITIES
If you have time and the required materials, consider
performing these optional activities:- Use iodine fuming to treat a sample, and allow the
revealed fingerprints to fade. (You can hasten this
process by putting the sample in direct sunlight or by
heating it very gently in the oven.) Retreat that sample
using ninhydrin and/or silver nitrate to verify that the
iodine fuming was fully reversible. - Test one or more of the methods using samples on
porous materials other than paper. For example, you
might try raising fingerprints on samples of fabric,
leather, or unpolished wood. - Treat samples on paper or other porous materials
after allowing different periods to elapse after
creating the samples. For example, produce three
similar samples on paper. Treat one of the samples
immediately, treat one after a day has elapsed, and
treat the third after one week. Do the results differ?
If so, is one of the methods better than another at
achieving results for older samples? - Produce samples after liberally applying petroleum
jelly or cream to your hands and then wiping them off.
Are the latent prints in such samples easier or more
difficult to raise? Is one or another of the methods
better or worse at revealing such latent prints? If so,
propose an explanation.
dISoALp S : dilute all solutions with at least three or
four times their volume of tap water and then flush them
down the drain with plenty of water.1.f you have not already done so, put on your splash I
goggles, gloves, and protective clothing.- Place one of your samples on a flat surface and spray it
with the silver nitrate solution until it is just slightly damp. - Expose the treated sample to direct sunlight or a UV lamp,
and observe it every few minutes to determine progress.
The latent fingerprints should become visible, first as a
pale yellow/purple color. With continued exposure, the
prints gradually darken, eventually becoming black. The
time needed to develop the prints completely may vary
from a couple of minutes to an hour or more, depending
on the particular fingerprint, the type of surface, and the
intensity of the light. Exposing the sample too long will
eventually cause the excess silver nitrate to be reduced to
metallic silver, staining the entire sample. - Once the prints are fully developed, bathe the sample in
water to remove the excess silver nitrate and “fix”
the print.
RQEWEvI UESTIOnS
q 1 : What common household substance is also used to reveal latent fingerprints? (Hint: search the Internet for cyanoacrylate.)
q: 2 Other than primates, very few mammals have fingerprints. There is one mammal, though, that is not a primate but produces
fingerprints that are almost impossible to discriminate from human fingerprints, even using current instrumental methods. What is
this mammal? (Hint: search the Internet for “mammal” and “fingerprints.”)