Answer:
Personification
Step-by-step explanation:
Personification is a literary device in which human characteristics are attributed to something non-human, e.g. an animal, object, or idea.
It is used in the given line from Sara Teasdale's poem Barter. The white hour of peace is described as singing. An hour can't sing in real life. It's something that people do. This is why the hour can be described as personified.