I suggest you do a close reading of chapter 4, going through this line by line. Write down the devices Dickens uses - for example - does he use metaphors? Does he use alliteration? Write down the quotes that back this up. What else does he do to convey fear? Does he repeat certain phrases, or use words which would evoke fear? Is darkness used? What of Scrooge himself? What are his thought processes? What does he say?