386 DIY Science: Illustrated Guide to Home Chemistry Experiments
SBSTITUTIU oNS ANd modIfICATIoNS- This test reacts to human or animal blood, so you may
use fresh meat as a source of blood. - You may substitute small pieces of filter paper for the
cotton swabs.
LABORATORY 22.1:
USE THE SHERLoCk HoLmES TEST To dETECT BLood
Until the early twentieth century, forensic
scientists had no reliable test for blood. The best
method available was to examine the suspected
blood stain with a microscope to detect the
presence of red blood cells. Unfortunately, this
microscopic test was considered unreliable
unless the blood stains were very fresh. Many
probable murderers escaped justice because
their attorneys claimed that apparent blood
stains could be rust or even red paint, claims
that forensic scientists at that time were unable
to refute definitively.
RIREEqU d EqUIpmENT ANd SUppLIES£ goggles, gloves, and protective clothing£ dropper or Beral pipette (3)£ sample of dried blood£ sample(s) of rust and/or other materials that look
like blood stains£ cotton swabs to collect samples£ distilled or deionized water£ ethanol, 70% (a few drops per test)£ kastle-meyer solution (a few drops per test)£ hydrogen peroxide solution, 3%
(a few drops per test)In 1901, Dr. Joseph H. Kastle of Kentucky University introduced
a simple, cheap, reliable presumptive test for blood. This test,
with modifications suggested by another forensic scientist,
became known as the Kastle-Meyer test, and is still used today.
But I think this test may actually have been devised in 1888 by a
forensic scientist whose name is known to everyone:
He seized me by the coat-sleeve in his eagerness, and drew
me over to the table at which he had been working. “Let us
have some fresh blood,” he said, digging a long bodkin into
his finger, and drawing off the resulting drop of blood in a
chemical pipette. “Now, I add this small quantity of blood to aBy the late nineteenth century, forensic toxicology was well
developed. Hundreds of specific forensic tests had been
devised. A forensic chemist still had to know what he was
looking for, but if that substance was present, the tests would
identify it. Reliable chemical tests had been devised for most
common poisons, and would-be poisoners could no longer
assume that poisonings would go undetected. In the early
twentieth century, the world-renowned forensic scientist
Bernard Spilsbury was testifying for the prosecution at the trial
of an accused murderer, when he was asked by the prosecutor if
common poisons could be detected reliably in the lab. Spilsbury
testified that all common vegetable and mineral poisons could
easily be detected, with only one exception. At that point, the
judge ordered Spilsbury to stop speaking, concerned that he
might reveal the name of this “undetectable” poison. (That
poison was aconite, derived from the plant monkshood, which
is lethal in doses too small to be detected by any means at that
time, and remains difficult to detect today.)
Although early forensic chemists devoted most of their efforts
to detecting and identifying poisons, forensic chemistry soon
expanded into other areas, notably the unambiguous detection of
blood and revealing latent (hidden) fingerprints. Modern forensics
laboratories now substitute instrumental analysis for much of
the “wet chemistry” that was used formerly, but wet chemistry
remains important, particularly for field work. In fact, the majority
of forensics tests done today are wet chemistry field tests. When
police officers or drug enforcement agents confiscate a substance
they believe may be an illegal drug, they use presumptive tests
on a sample of the suspect material. Presumptive tests are not
perfect—they can produce false positives and false negatives—but
they’re a fast, inexpensive, and reasonably reliable way to confirm
or deny the presence of a particular compound (such as cocaine)
or class of compound (such as opioids).The laboratory sessions in this chapter explore various aspects
of forensic chemistry.