"Cold enough to freeze the balls off a brass monkey."

 
      Every sailing ship had  to have cannon for protection. Cannon of the times
used round iron cannonballs.  The master wanted to store the cannon balls
such that they could be of instant  use when needed, yet not roll around
the gun deck.
      The solution was to stack them up in a square-based pyramid next to
the cannon.  The top level of the stack had one ball, the next level down
had four, the next  had nine, the next had sixteen, and so on. Four levels
would provide a stack of  30 cannonballs.
     The only real problem was how to  keep the bottom level from sliding
out from under the weight of the higher  levels. To do this, they devised a
small brass plate ("brass monkey") with one  rounded indentation for each
cannonball in the bottom layer. Brass was used  because the cannonballs
wouldn't rust to the "brass monkey", but would have  rusted to an iron one.
     When temperature falls,  brass contracts in size faster than iron. As
it got cold on the gundecks, the  indentations in the brass monkey would
get smaller than the iron cannonballs  they were holding. If the
temperature got cold enough, the bottom layer would  pop out of the
indentations spilling the entire pyramid over the deck.
     Thus it was, quite literally, "cold enough to  freeze the balls off a
brass monkey."

Just thought you might like to  know.....................


 

from snopes.com 

Origins:   Somebody's fanciful imagination is at work cooking up spurious etymologies again. In short, this origin for the phrase "cold enough to freeze the balls off a brass monkey" is nonsense because: 

Not even the venerable Oxford English Dictionary, records a usage of "brass monkey" like the one presented here. 

When references to "brass monkeys" started appearing in print in the mid-19th century, they did not always mention balls or cold temperatures. It was sometimes cold enough to freeze the ears, tail, nose, or whiskers off a brass monkey. Likewise, it was sometimes hot enough to "scald the throat" or "singe the hair" of a brass monkey. These usages are inconsistent with the putative origins offered here. 

Warships didn't store cannonballs (or "round shot") on deck around the clock, day after day, on the slight chance that they might go into battle. Space was a precious commodity on sailing ships, and decks were kept as clear as possible in order to allow room for hundreds of men to perform all the tasks necessary for ordinary ship's functions. (Stacking round shot on deck would also create the danger of their breaking free and rolling around loose on deck whenever the ship encountered rough seas.) Cannonballs were stored elsewhere and only brought out when the decks had been cleared for action. 

Particularly diligent gunners (not "masters," who were in charge of navigation, sailing and pilotage, not ordnance) would have their crews chip away at imperfections on the surface of cannonballs to make them as smooth as possible, in the hopes that this would cause them fly truer. They did not leave shot on deck, exposed to the elements, where it would rust. 
Nobody really knows where the phrase "cold enough to freeze the balls off a brass monkey" came from, but the explanation offered here certainly isn't the answer. 

 

of Nautical Interest