Hour One: what will burn
Nudge. You need four hours of fire. Add up everything on the tally that is allowed to burn.
Harder
Chairs, settle and shutter bars together come to three and a half hours, and the Bible is not to be burnt. One thing lasts four hours by itself, and the girl has just told you why it should go.
The hour, in words
Tobias's tally lists five things that would burn. Below it are five buttons in two rows: The chairs, The settle and The shutter bars across the top; The great Bible and The London chest below. Tap one and then Put it on the fire.
The answer
The answer is chest.
Four chairs at a quarter of an hour, the settle at two hours and two shutter bars at a quarter each make three and a half hours, which runs out before first light. Only the London chest lasts four hours on its own, and it is the chest the maid unpacked: burning it keeps the fire and gets rid of what made her sick.