1

Blood?

Is it blood?

2

Presumptive Tests for Blood

No longer used

Benzidine test

Toxic

1

3

Presumptive Tests for Blood

Kastle-Meyer test

2

Phenolphthalein

Benzidine test

1

4

Presumptive Tests for Blood

Luminol test

3

Kastle-Meyer test

2

Benzidine test

1

5

Presumptive Tests for Blood

Based on peroxidase properties of blood

H

2

O

2



H

2

O + O

6

Kastle-Meyer Test

Acid form

Colourless

7

Kastle-Meyer Test

Alkali form

Pink

8

Kastle-Meyer Test

Zinc

(reduce)

Colourless

Reduced form

H

2

O

2

, blood

(oxidise)

Alkali form

Pink

9

Kastle-Meyer Test

Zinc

(reduce)

H

2

O

2

, blood

(oxidise)

10

Kastle-Meyer Test

Suspected bloodstain

Add reduced phenolphthalein

Add H

2

O

2

2

1

Turn pink

Most likely blood

11

Kastle-Meyer Test

Powerful enzymes in potatoes

Catalyst for reaction

Turn pink

“False positive”