When a bone is soaked in acid, it loses its rigidity. Acids react with the calcium in bone; without calcium, bones become soft and pliable. This process occurs both in nature and in laboratory conditions.
The softening of bones also occurs within living organisms when acids are consumed. The phosphoric acid found in soft drinks is more closely linked to calcium loss than other dietary acids. In a Tufts University study, cola drinkers have an average bone density 4 percent lower than individuals who do not drink soft drinks that contain phosphoric acid.
When the process is carried out intentionally in a laboratory, it is called bone decalcification. Bones are soaked in a chelating agent to remove the calcium. The resulting softer bones are easier to cut into small sections for sampling and analysis. This process takes days or weeks, with larger bones requiring a longer span of time to decalcify fully.
The stronger an acid is, the more quickly it decalcifies bone. Loss of bone density associated with the phosphoric acid in soft drinks occurs over a span of decades. Decalcifying animal bone with weak household acids is a common classroom science experiment that takes several days and requires regular replenishment of the acid.