Science corner

Sophie Duncan keeps her cool

How did we keep things cool before the invention of the freezer?

Initially ice was recovered from canals, ponds and rivers, and stored in ice houses - insulated buildings underground. The ice wasn't very clean, and was used indirectly to cool drinks, etc.

From the 1820s ice was imported from Norway. It was much cleaner, and was stored in specially built ice wells.

An example of one of these now houses the London Canal Museum. The ice was used to make ice-cream and fruit sorbets, as well as being sold to shops and restaurants to keep their food cold.

Ice provides wonderful opportunities in the classroom. It is easily made, and stored, and when you have finished the experiment you can wipe it up.

Put some water into a glass and add a layer of vegetable oil. Place an ice cube in the top and you've made a type of "lava lamp".

As the ice melts the water sinks to the bottom of the glass, taking some oil with it. The oil returns to the top of the glass. This continues until the ice has all melted.

Can you pick up an ice cube with a piece of string? You can if you put some salt on the top of the ice cube before you start.

Leave the string on top of the ice cube for a minute and then lift the ice cube up. This is possible because the ice melts and refreezes, trapping the string.

Sophie Duncan is a physicist and programme manager with Science Year www.scienceyear.com

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