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Showing posts from June, 2014

How to test Blood: Confirmatory Tests in Forensic Practice

Preliminary examination of blood stains do not confirm the presence of blood. It merely indicates that the positive stain might be due to blood.
In order to confirm the identity of blood, there are certain crystal and spectroscopic tests that are regularly employed in the forensic science laboratories.

1. Takayama Test:

Reagent Preparation:

Standard Glucose Solution (100g/100ml) 3 ml
10% Sodium hydroxide (NaOH) 3 ml
Pyridine 3 ml
Distilled Water 7 ml
Reagents should be made fresh daily.

1. Place material to be tested on a microscopic slide and cover with a cover slip.
2. Add a drop of Takayama Reagentand allow to flow under the cover slip.
3. Warm slide gently at 65oC for 10-20 seconds
4. Allow to cool and observe under microscope at 100X magnification.
The appearance of pink needle shaped crystals of pyridine hemochromogen (Pyridine ferroprotoprophyrin) is positive reaction for heme.

2. Teichmann’s Test:

Reagent Preparation:
Potassium Chloride or 0.1 g
Potassium Bro…

How to test Blood: Preliminary Tests in Forensic Practice

Blood is an important evidence in many criminal cases. A forensic scientist frequently finds blood as an evidence of a crime. In a forensic investigation, blood as an evidence can answer a lot of questions. For example, it can establish that a crime has taken place, it can also establish the identity of a victim and suspect. Besides, blood evidence can also provide clues as to how the act of crime had taken place. There are several tests that can be performed on a suspected sample for the identification of blood. The standard procedure of a forensic science lab is to first apply the preliminary tests on the samples to screen out non-blood samples from the actual blood. Once the preliminary tests give positive results, the more comprehensive confirmatory tests are performed in order to establish that the positive samples are indeed blood. Preliminary Tests for Blood: Here are some of the most common preliminary tests. 1. Kastle-meyer test: Theory: This test is based on the fact that blood c…