Another simple experiment to check how much carbonic acid was present was described in advice books and school textbooks. The Science of Home Life, a book designed for schoolgirls, instructed that ‘if we pour some clear lime water into a shallow dish or saucer, and leave it exposed to the air for an hour or so, we shall find a whitish crust or scum on the surface of the liquid. This proves that carbonic acid is present in the air.’
