CHAPTER 13: The Pirates' Raid.
As soon as it was daylight next morning, Francis was up and at work.
His experiments of the evening before were at once confirmed.

Three or four hours' work would enable him to free his wrists, but he could make no impression on the rivets at his ankles.

After a few trials he gave this up as hopeless, for he was afraid, if he continued, he would blunt the edge of the dagger.
For an hour he sat still, thinking, and at last an idea occurred to him.

Iron could be ground by rubbing it upon stone, and if he could not cut off the burr of the rivet with the dagger, he might perhaps be able to wear it down, by rubbing it with a stone.
He at once turned to the walls of his cell.

These were not built of the unbaked clay so largely used for houses of the poorer class in Northern Egypt, but had evidently been constructed either as a prison, or more probably as a strong room where some merchant kept valuable goods.