MAKING A FIRE EXTINGUISHER:

ITEMS REQUIRED:

Iodine crystals: 3 gm-Methylated spirit: 30cc-Washing soda: 20gm-Water: 30cc-A beaker of 250ml-One glass rod-A spirit lamp

PROCEDURE:

Take about 20gm of washing soda (sodium carbonate) and dissolve it in 30cc of water in a beaker. Mix 30cc of water in a beaker. Add 3gm powder of iodine to this mixture and warm the beaker on the flame of a spirit lamp. Do not heat it. Go on stirring. A yellow shining solid will separate. Let the mixture cool. Dry the yellow solid on a blotting paper. This is used as iodoform. To make tincture iodine, take 5gms of iodine crystals and dissolve them in 5gm of potassium iodide solution prepared in 10cc of water. To this mixture add 250cc of rectified spirit. Your tincture iodine is ready. It can be used in healing wounds.

DETERMINING THE SURFACE TENSION OF A LIQUID:

ITEMS REQUIRED:

One thin plastic sheet 5cmX5cmX3mm-Thread-One wooden block 10cmX10cmX2cm-Two wooden strips, 0.25cmX1.5cmX1cm each-Iron nails, one iron ring of about 5cm diameter, one pin-One bowl of water (or the liquid whose surface tension is to be measured)

PROCEDURE:

To measure surface tension, you have to make a balance device. For making the balance, take a wooden block and glue a wooden strip at its centre. Make the beam of the balance by using another wooden strip and using a pin as a pivot. Take the iron ring and a make a small bag of cloth. Tie three threads to make a pan of the balance. Take the plastic sheet and put a tiny hole in the centre with a needle. Tie a knot in a thread and use it to suspend the plastic sheet from one end of the balance. Use small nails on the other end to balance the plastic sheet. Now, bring the bowl full of water and put it under the plastic sheet in such a way that it just touches the surface of water. You will see that the balance is disturbed. Now, add small nails in the pan until the plastic sheet suddenly breaks away from the surface of water. This extra weight is nothing but a measure of the surface tension the water. You can repeat the experiment by using kerosene, alcohol, mustard oil, etc. instead of water.