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Home Experiments

EXCRETORY SYSTEM

Plants in the Dark make CO2

Safety rules:
Parent supervision
Take care with fire or heat
Materials you need are:
a clear container with an airtight lid
water plants from a fish tank or lake
water
a dark cupboard
matches
a friend

Put the water and water plants in the clear jar and put the lid on tightly. Place it in a dark cupboard for a day. Timing is important here - Light a match and have your friend take of the lid at the same time. Quickly put the lit match in the opening of the jar. It should go out.

Plants respire, that is, take in oxygen and give out carbon dioxide as animals do. If they are in the dark, they cannot photosynthesise to make oxygen. The air in the jar after a day in the dark will be mostly carbon dioxide and extinguish the lit match.

Taking Fingerprints

Materials you need are:
printer’s ink (preferably fast-drying and paste-like)
a sheet of glass
a soft rubber roller
a sheet of paper
a magnifying glass

Place a few drops of ink onto the glass inking plate and roll it to an even thin film on the surface.

Ink the fingers individually by "rolling" the first joint of each finger over the inked surface.

Now lightly press the inked part of the finger onto the paper, again by a slight rolling action.

Continue until you have produced ridge patterns of all 10 fingers.

Examine them with a magnifying glass.

Developing or ‘Fixing’ Latent Fingerprints

Fingerprints at the crime scene are likely to have been deposited in one of 3 ways:

  • As an impression in a soft substance such as soap or wet paint
  • A print made by a substance such as dirt deposited on the finger
  • The sweat and oil deposit from the skin

In the first 2 cases, the print is obvious and can be photographed by angling against the light, or by "lifting" it with sticky tape. Lasers or UV light are now used also.

If the fingerprint is difficult to see, it may need to be "fixed" to make it visible before photographing.

Materials you need are:
fine dusting powder such as carbon
a camel hair brush

After dipping the brush into the powder, dust the print until visible.