How to prove that the flexibility of the bone is given by organic substances?

You can do an experiment. You need to take a chicken bone and dip it in vinegar. It is advisable to take 70% vinegar, as with 9% it will take a very long time. The acid is able to remove minerals from the bone. Accordingly, only organic matter will remain there. After a few days, the bone will become flexible, since there are practically no minerals left. It also confirms the fact that with age, bones become harder due to the fact that organic matter is removed and replaced by mineral.