0.2 Forensics lab  (Page 4/4)

3. When you can see the fingerprint clearly, remove the filter paper using tweezers and keep it until the end of the lab.

Part 1b: Latent Fingerprint Development using fuming cyanoacrylate.

Materials

Large hotplate

Large glass dish for fuming chamber

Metal Cans (2)

Superglue Water

Glass slide

Experimental Procedures

***This experiment should be conducted in the hood***

• Place finger prints on glass slide. Alternately, small objects that contain fingerprints can be placed in the chamber.
• Make sure one pan has water in it.
• Place a drop of superglue the size of a nickel onto the other can top.
• Place glass slide inside the fuming chamber.
• Turn the hotplate on low and allow the fingerprints to develop for approximately ten minutes.
• Turn the hotplate off and remove the fingerprint specimen. Allow it to cure for approximately 5 minutes.

Caution! Overheating cyanoacrylate can produce highly toxic hydrogen cyanide gas. The reaction should take place in a well ventilated area with the hot plate on low.

Caution! Superglue can bond instantly to fingers and other body parts. Take caution in using it. In the event of an inadvertent bonding, use acetone to soften the glue.

Part 2: Ink Identification

1. Obtain a precut TLC plate. Do not touch the white surface and handle carefully only by the edges.

2. Using a pencil, draw a light line across the shorter dimension 1 cm from the bottom. Using a ruler as a guide on the line, mark off five equally spaced intervals on the line as shown in Figure 1.

Figure 2. TLC plate

3. Scribble on a small piece of paper with each of the pens and dissolve the ink with a drop of ethanol. The dissolved ink can now be spotted onto a pencil line drawn in step 2. Repeat step 3 for each pen. Do exactly the same procedure for the unknown writing sample that you can obtain from your TA.

4. Use a 400 mL beaker for the development chamber. Add the solvent mixture (ethyl acetate/ethanol/water) to the beaker to a depth of about 0.5 cm. Remember: the level of the solvent must be below the spots on the plate. Using tweezers or forceps, place the spotted plate in the development chamber so that it rests in the solvent and against the beaker wall. Cover the beaker (with a paper towel) and allow the plate to develop. It might take more than 10 min, so you can proceed with Part 3 and Part 4.

5. When the solvent has risen on the plate to within 1 cm from the top, remove the plate from the beaker with tweezers or forceps. Using a pencil, mark the position of the solvent front.

6. Allow the plate to air dry and observe the colored separation. Note how many dye components make up the individual pens.

Part 3: Invisible Ink

8. Using a millimeter ruler, measure the distance that each spot (use the center of each spot for consistency) has traveled relative to the solvent front. Calculate the $R_f$ values for each spot. Part 3: Invisible Ink

Method 1

1. Pour a little milk in a beaker. Soften the point of a toothpick in the milk and write a letter or a message with it. Do not use too much milk otherwise the paper will wrinkle. Let the paper dry completely.

2. Place the piece of paper on a warm hot plate and wait until the message appears.

Method 2

1. Cornstarch has been prepared for you by mixing 1 g of cornstarch with 10 mL of water in a beaker and stir until smooth.

2. Heat the prepared mixture for several minutes. Soften the point of a toothpick in the mixture and write a letter or a message with it. Let the paper dry.

3. To observe the message, place it in a jar with iodine vapor in the hood. Recap the jar and let it stand for more than 1 minute.

Method 3

1. Pour about 5 mL of phenolphthalein solution in a beaker. Soften the point of a toothpick in the solution and write a letter or a message with it. Allow the paper to dry.

2. To read the invisible writing, dip a small piece of cotton wool into the 1 M NaOH solution and carefully wipe the paper (do not rub!).

Part 4: Breathalyzer

Caution! Sodium dichromate is a strong oxidizing agent. Avoid contact with the skin.

1. Pour 2 mL of ethyl alcohol into a test tube and add 2 mL of acidic sodium dichromate solution. Mix gently and record your observations.

Part 5:Luminol Analysis

1. The luminol solution (solution 1) has been prepared for you by dissolving 0.1g of Luminol in 20 ml of 10% NaOH in a 50 ml beaker and diluting this solution to 200ml in your spray bottle and set aside.

2. The fake“blood”solution (solution 2) has been prepared for you by dissolving 0.5g of $K_3[\text{Fe}(\text{CN}{)}_6]$ in 20 ml of 5% hydrogen peroxide solution.

3. In the hood blacked out by construction paper smear some“blood”(K3[Fe(CN)6] in 5% hydrogen peroxide) onto a piece of paper towel with a cotton swab. (make sure you are wearing gloves)

4. Quickly spray the wet“blood”stain with the luminol solution (solution 1) and close the hood to the point that you can barely see at the bottom and record your observation.