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Cold enough to freeze the balls off a brass monkey

I know, most of you are thinking. What is he doing writing a blog about such a topic.
Well just to prove that most of you assume you know what this about when in reality you need to read the rest of this blog.

The phrase “Cold enough to freeze the balls off a brass monkey” came from the early 1700′s when sailors would stack iron cannon balls on a brass platform called a “Monkey”

When the weather would turn really cold and the temperature would drop drastically the brass monkey metal would contract more than the iron cannon balls and the cannon balls would roll off the brass monkey platform.

Thus the phrase ‘Cold enough to freeze the balls off a brass monkey” was originated.

Now aren’t you glad you read the entire blog and didn’t just assume I need professional help.
Enjoy winter, bundle up and make a snowman if you get a chance.

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  1. Posted October 1, 2012 at 7:58 pm | Permalink

    Freeze the balls of a brass monkey.
    I had heard the derivation of the term before, however I don’t believe thermal contraction of brass to be the cause of the cannon-balls being dislodged. Iron also has a thermal expansion coefficient, so the cannon-balls would also shrink in cold weather.
    Brass has a thermal expansion coefficient of 0.000019 per degree Celsius i.e. a 1 meter bar of brass will grow 1.9 mm if its temperature increases 100 degrees C.
    Iron has a thermal expansion coefficient of 0.0000118 per degree Celsius i.e. a 1 meter bar of iron will grow 1.18 mm if its temperature increases 100 degrees C.
    We are considering contraction not expansion but the principle is the same. Here is a rough explanation of the mathematics. If we consider that both the brass and the iron are contracting then the difference in contraction is actually 1.9-1.18 = 0.72mm per metre per 100 degree change in temperature. Say a cannon-ball diameter is 100mm and there is a row of 4 cannon-balls sitting in line on the bottom row of the 16 hole brass monkey, that is 400mm length or 0.4 of a metre. The cannon-balls would have to be touching to push the balls out of the brass monkey if the theory were correct. A 100 degree change in temperature would result in a 0.288mm change in differential length. The end balls would only be displaced by half of this measurement (0.144 mm) as the displacement of the balls would be evenly dispersed from the centre. Actually less than this as the length of the outer ball beyond the indentation it sits in does not count in the equation but I’ll ignore it for the purpose of simplification.
    Let’s say the brass monkey was made on a pleasant spring afternoon when the temperature was 20 degrees. It was loaded onto a warship ship and loaded with its 30 cannon-balls. Said ship then sails to the Artic where it experiences temperatures of -40 degrees. The temperature difference is 60 degrees – the contraction difference of the brass monkey and the cannon-balls is 60% of the 100 degrees mentioned above i.e. 0.0864 mm.
    A cannon-ball being pushed off centre by 0.0864 mm would not be enough to dislodge the load of cannon-balls. To be functional brass monkeys would have to withstand the rolling of a ship. Cannonballs and brass monkeys would not have been manufactured to such fine tolerances that a change in temperature would cause this problem. Sailors spent time chipping rust scale off cannonballs to prevent them becoming too large and so they would fit down the muzzle. They were not a precise diameter or evenly round.
    A more likely explanation is ice heave. The cannon-balls got covered in water which froze. The ice expanded and pushed the balls apart. More water gets between the balls, freezes and expands until the balls are pushed off the brass monkey. Ice heave is a powerful force, just think of the effect it has on nature such as splitting huge rocks.
    Actually any old Australian swagman would know this from the days when they were forced to seek shelter from the freezing rain in an old bark hut. Overnight the rain would seep through the bark walls and the wind chill would freeze the wet walls and cause them to fall from the sides of the hut. Hence the term “freeze the walls off a bark humpy”.
    Just joking.
    Tom Hanson

  2. Andrea Hana
    Posted June 26, 2013 at 10:00 am | Permalink

    Tom Hanson,
    Thanks for the comment, very enlightening!

    I did not think that metal contraction would occur so significantly that it would cause cannon balls to fall from the monkey, but your suggestion of water or ice expansion makes sense. Thus, the phrase still holds true.


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