Definition of "veronal"

He was by now so worn out that he could not resist my firmness. I gave him a sufficient dose of veronal to insure his unconsciousness for several hours. I thought that was the best service I could render him.

1919, W. Somerset Maugham, chapter 29, in The Moon and Sixpence

She died of an overdose of veronal. She's been taking it lately for sleeplessness. Must have taken too much.

1926, Agatha Christie, chapter 1, in The Murder of Roger Ackroyd