What motivation does Sydney Carton have for purchasing the contents of the bottles from the chemist in Chapter 9 Book the Third?A Tale of Two Cities by Charles Dickens
After Miss Pross recognizes her brother Solomon in Book the Third, ChapterVIII of A Tale of Two Cities in a wineshop in Paris, she calls to him; discomfitted, he cautions her to not call her Solomon. For, Basard is the man that she recognizes as her lost brother. Telling her to step outside, the reluctant brother talks to her, but only after Sydney Carton appears and recognizes Solomon as John Basard.
Carton takes Basard aside and talks with him, informing him that he knows of Basard's being a double spy, "a Sheep of the Prisons," and a spy for the English. In fact, Carton connects Basard with Roger Cly, the English spy that is supposed dead. He discusses present matters with Basard and makes future arrangements. The discussion, however, is yet shrouded in mystery; further, Carton's actions are mysterious, as well, as he walks to a chemist's shop where he purchases two very volatile substances that the chemist cautions him not to mix. Here, of course, is a suggestion of poison. For, shortly thereafter Carton recalls the funeral of his father and the words of Jesus the Savior read by the minister, "I am the Resurrection and the Life."
Clearly, in this there is the introduction of spiritual redemption along with the motif of doppelgangers as Basard is discovered to be a double spy and there appears to be some duplicity planned on Sydney's part as he talks with Mr. Lorry about his long life and how endeared Lucie is to him. He later walks on a bridge and sees the end of the night as
... the moon and the stars turned pale and died, and for a little while it seemed as if Creation were delivered over to Death’s dominion.
After this, Darnay is retried and a letter of prisoner Manette denouncing the Evremondes is read by M. Defarge.