This is a fun experiment, it does involve heat so you do have to be careful and have a responsible adult when carrying out this investigation.
As you can see in this photo the glue we made was strong enough to stick two boxes of eggs together and hold the weight of the six eggs in the bottom box! Pretty impressive!
For this scientific investigation I will take you through step by Step explaining the science behind it as we go. First you will need:
Bicarbonate of soda
A disposable plastic cup
Put 150ml of milk in a pan and add 5ml of white vinegar.
By adding the acid, the vinegar, to the milk you create a chemical reaction that separates the milk; you will notice that the milk will curdle, stir it on a gentle heat and the curds, the white clump, will separate from the whey, the liquid.
STEP TWO Drain off the whey and add a little, 10ml or so, of water to the curds in the pan, and 5ml of bicarbonate of soda.
The curds are milk protein, called casein. Liquid casein is a natural glue. When we add the bicarbonate of soda it neutralises the acids left over from STEP ONE. The bubbles that are produced are filled with Carbon dioxide a gas that is produced during the reaction between the acid and the base.
Gently simmer the mixture until the curds breakdown into a liquid again, then keep heating it until the mixture thickens, it should be the consistency of PVA glue. The curds, the casein, become liquid again. N.B: you will notice that it will foam and froth like egg whites whisked at first but this will reduce as the carbon dioxide leaves the mixture.
STEP FOUR Glue something together like two egg boxes! How strong is the glue? How much weight can it hold?