Presentation on theme: "Is It Blood? Olivia Carran 7AY Science January 16, 2011 Class of Mrs. Gateau St. Mary’s School."— Presentation transcript:
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.
0 1.0 2.0 3.0 4.0 5.0 6.0 Color Intensity Units Substances Tested in Hemastix Reaction Distilled WaterBeef Blood Figure 1. Hemastix test results with water (negative control) and beef blood (positive control). Each bar represents the average color intensity of four runs.
0 1.0 2.0 3.0 4.0 5.0 6.0 Color Intensity Units Substances Tested in Hemastix Reaction AppleHorseradish Figure 2. The Hemastix test incorrectly identified some food substances as blood. Tabasco
0 1.0 2.0 3.0 4.0 5.0 6.0 Color Intensity UnitsSubstances Tested in Hemastix Reaction AmmoniaBleach Figure 3. The Hemastix test incorrectly identified bleach as blood.
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.
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