Is It Blood?
Olivia Carran
7AY Science
January 16, 2011
Class of Mrs. Gateau
St. Mary’s School
Introduction
• Blood evidence from a crime scene is used in court to
convict criminals.
• The Hemastix test is used to identify blood at a crime
scence.
• Hemastix contain chemicals that react with proteins
in blood. If blood is present, the Hemastix test forms
a colored, dark green dye.
• We tested if the Hemastix test accurately identifies
blood.
Hypothesis
• If blood is present at a crime scene, then it will
be correctly identified using a Hemastix.
Materials
These are the materials I used to test with the Hemastix.
Methods
1. Put each of the following substances in a separate bowl: real blood (from the
bottom of a meat tray); bleach; ammonia; Tabasco sauce, horseradish; ground
apple, ketchup; red food coloring.
2. Wet a cotton swab with distilled water and dip the swab in one of the substances.
3. Immediately press the cotton swab against the indicator tab on the Hemastix strip.
4. Wait 10 seconds for the Hemastix chemical reaction to develop. Observe and
record the color intensity change. Use the color strip on the Hemastix bottle to
assign a number (0-6) to each color.
5. Do four separate runs for each substance.
6. Wash hands with soap and water to avoid contaminating next test. Repeat steps 2
– 6 for each of the substances in step 1.
7. Calculate the average color intensity produced by each substance. Graph the
average color intensity of each substance compared to the average color intensity
of real blood.
This shows how I was holding the cotton swab dipped in beef
blood to the end of the Hemastix.
Hemastix Color Intensity Scale
• Color
intensity
scale is numbered
from 0 – 6.
• Zero is the yellow
color at the bottom.
•Six is the dark
green color at the
top.
Results
• My results, shown in Figures 1-3 below,
demonstrate that the Hemastix test did not
specifically identify blood.
• The Hemastix test incorrectly identified many
substances as blood in my experiments.
Figure 1. Hemastix test results with water (negative control) and beef
blood (positive control). Each bar represents the average color
intensity of four runs.
Color Intensity Units
6.0
5.0
4.0
3.0
2.0
1.0
0
Distilled Water
Beef Blood
Substances Tested in Hemastix Reaction
Figure 2. The Hemastix test incorrectly identified some food
substances as blood.
Color Intensity Units
6.0
5.0
4.0
3.0
2.0
1.0
0
Apple
Horseradish
Tabasco
Substances Tested in Hemastix Reaction
Figure 3. The Hemastix test incorrectly identified bleach as blood.
Color Intensity Units
6.0
5.0
4.0
3.0
2.0
1.0
0
Ammonia
Bleach
Substances Tested in Hemastix Reaction
Discussion
• I tested foods that may be present in the state
of a crime scene. Ketchup did not test like
blood.
• Bleach, used by criminals to remove blood
evidence, was also identified as blood by
Hemastix.
• My results suggest that the Hemastix test is
not always accurate.
Results showing a positive reaction with beef
blood
Results showing a negative reaction with
ammonia
Results showing a positive reaction with
horseradish
Conclusion
• My results did not support my hypothesis
because the Hemastix test incorrectly
identified some substances as blood even
though they were not blood.
• Based on my results, I recommend that
forensic scientists be very careful when using
the Hemastix test to identify blood stains at a
crime scene.
Bibliography
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Helmenstine, Anne Marie. Crime Scene Chemistry – Test for Blood. About.com:Chemistry, 1 March 2009. Web. 18
November 2010.
Murfin, Melissa. Crime Scene Identification of Human Blood: Forensic Testing Used to Identify Blood Spatter
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Schiro, George. Collection and Preservation of Blood Evidence from Crime Scenes. Crime Scene Investigator
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