This week, Roy decided it was time to do an experiment. He had been reading Roald Dahl’s book ‘Georges Marvellous Medicine’, and wanted to have a go at making his own version. The question was, how? His Grandma was cooking red cabbage for dinner and decided to give him a surprise by doing some ‘magic’ with the cooking liquid. She put some in a glass and added a little household cleaner and wow – suddenly instead of being purple the liquid was green! Roy thought this was amazing, and decided that not only did he want to see what other things he could add to change the liquids colour, but that he wanted to show his friends how to do it too.
NOTE: This medicine is purely for the appearance. DO NOT drink it!
You Will Need:
- Red cabbage
- Water
- A saucepan
- Clear, disposable plastic cups
- Masking tape and a pen
- A variety of household products. You will need an adult to help with the adding of these, and Roy suggests you don't use dangerous household chemicals like drain cleaner. You can get good reactions with less dangerous things. Roy called these ‘additives’ and used:
- Cloudy ammonia (this smells pretty bad and you shouldn't breath the fumes)
- Dishwashing powder
- Washing up liquid
- Clothes washing powder
- Antacid
- Yogurt
- Citric acid
- Cream of Tartar
- Bicarb soda
- Lemon Juice
- Vinegar
- Denture Cleaner
- Kitchen cleaner (Spray and Wipe or Ajax etc)
- Toothpaste
- Soft drink
Use your imagination! You can test whatever you like - just make sure they are safe!
- First, you need to thoroughly overcook the red cabbage. Roughly chop the cabbage, put in into a pot and then add some water. You will need enough water to boil the cabbage in. Put the cabbage on the stove and cook it, for at least half an hour. Warning – this will smell really bad, a bit like really, really dirty socks!
- Strain the cabbage liquid and throw away the overcooked cabbage. Pour the liquid into a jar and put in the fridge to cool off (and stop it going off).
- Prepare the disposable cups. You want one cup per ‘additive’, and so that you know what you added to each, pull off a strip of masking tape, stick it to the outside of the cup and write what you will add on it. Remember to keep one cup as a ‘control’ with only cabbage water in it!
- Dilute the liquid a little (if it seems very concentrated). After boiling your cabbage for so long, the liquid may be very concentrated (and very smelly). Add some water to it (about a ¼ of the total amount)
- Divide the liquid between your cups. You want about the same amount in each cup.
- Now, start adding things! Gently stir or swirl the liquid around once you have added things like citric acid, so that they dissolve.
- Watch the colours change! Some will be immediate, strong changes, and some will change over time. We left ours to finish changing for about 5 hours. You will see colours ranging from reds, pinks and purples to blues, greens and yellows.
- Line the cups up from most acidic (red) to most basic (yellow).
What Is Happening?
Red cabbage contains something called flavin, a natural ‘ph indicator’. When you boil the red cabbage you will find the water turns a vivid purple colour, having extracted the dye from the cabbage, but you will also have extracted the flavin.
So what is a ph indicator? Ph measures how acidic or basic something is. The Ph scale ranges from 0 to 14, with Ph less than 7 being acidic, greater than 7 being basic and 7 itself being neutral. A ph indicator is something which can be added to something (usually a solution) to tell you where on the ph spectrum it sits. Red cabbage juice does this by changing the colour of the solution. When you add a product to it, it will cause it to change colour depending on how acidic or basic it is.
When you use red cabbage as an indicator, you will discover that the more acidic, the redder the colour will become. Acidic solutions will range in colour from pink right into vivid reds. Purple, as the colour closest to the normal colour of red cabbage juice is the least acidic, and closest to the ‘control’ of normal red cabbage juice. Pink is in the middle while reds indicate very acidic solutions. The most acidic solution Roy tried was citric acid, then lemon juice, then vinegar. Even lemonade is acidic!
Base solutions will range in colour from blue to green to yellow. Blue, being the closest to the natural purple of red cabbage juice is the least ‘basic’, while green is in the middle and yellow indicates the most basic solutions. Roys most basic solution was made using dishwashing powder.
You will find that some products, when added to the red cabbage juice turn a range of purples. Sometimes, these changes are quite difficult to see, as they can be very subtle differences from the original purple solution. The greater the change, the less neutral a solution is. If the solution takes on a red tinge, it is on the acidic side of neutral, while if it takes on a blue tinge, it is on the basic side.