What chapter shows that Calvin is patient?

Calvin shows he is patient in the chapter called "The Transparent Column." This is a climactic part of the story: Charles Wallace has been taken over by IT and is leading Meg and Calvin through Central Central Intelligence to the place where IT is keeping Meg's father.
Charles Wallace is lost to them right now, so they can't rely on his wisdom and intuitive skills. Meg is exhibiting impatience. It falls to Calvin to have a level head. While Meg hurtles herself against the transparent column—and hurts herself—to try to get to her father, who is imprisoned inside, Calvin tries to connect with Charles Wallace. He tries to pull Charles Wallace's mind away from IT. One way he does this is to quote from Shakespeare's The Tempest, likening the imprisoned father to the spirit Ariel imprisons magically in the cloven pine.
Calvin's patient concentration on Charles Wallace almost pulls him back:

Calvin's intense voice hit at him. "Come back, Charles. Come back to us."
Again Charles shuddered. And then it was as though an invisible hand had smacked against his chest and knocked him to the ground, and the stare with which Calvin had held him was broken. Charles sat there on the floor of the corridor whimpering, not a small boy's sound, but a fearful, animal noise.

It is Meg's impatience to get to her father that breaks Calvin's attention away from Charles Wallace.