I'm reading Dickens' Hard Times, and I'm curious about the use of "thou" in Stephen Blackpool's dialogue. I'm aware that "thou" was the second-person singular pronoun (corresponding to "tu/vous or tu/voi in French and Italian), but I was under the impression that it had died out in the vernacular by the nineteenth century, and used only in particular circumstances – say, in poetry for the purposes of establishing a sense of intimacy with either the reader or the person the speaker is addressing (for example Keat's "When I Have Fears": "And when I feel, fair creature of an hour, / That I shall never look upon thee more"). In this particular instance, I had the thought that it might be an affected use – say, the organic beauty of the speeches of the lower class is used to highlight the monotony of Bounderby's diction – but I have no idea if its use was creative artifice or simply mimicry.

Basically, when did the use of "thou" die out in the vernacular? Was it dropped first by those in the upper class, before it was eventually dropped by the lower? What's the story here?