develop (v)

Definition: make visible by means of chemical solutions
Example: Please develop this roll of film for me.

ferment (v)
sour (v)
turn (v)
work (v)

Definition: go sour or spoil
Example: The milk has soured. The wine worked. The cream has turned--we have to throw it out.

acidify (v)
acetify (v)

Definition: turn acidic
Example: the solution acetified.

acid (n)

Definition: any of various water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt