He now felt certain that, with patience, he should be able to cut off the projecting edges of the rivets, and so be able to free his hands.  He, therefore, now examined the fastenings at the ankles.  These were more heavy, and on trying them, the iron of the rivet appeared to be much harder than that which kept the manacles together.  It was, however, now too dark to see what he was doing, and concealing the dagger again, he lay down with a lighter heart than he had from the moment of his capture.

Even if he found that the lower fastenings of the chain defied all his efforts, he could cut the rivets at the wrists, and so free one end of each chain.  He could then tie the chains round his legs, and their weight would not be sufficient to prevent his walking.

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.  It was therefore constructed of blocks of hard stone.

It seemed to Francis that this was sandstone, and to test its quality, he sat down in the corner where the guard had, the night before, placed his supply of food and water.  First he moistened a portion of the wall, then he took up a link of his chain, and rubbed for some time against it.  At last, to his satisfaction, a bright patch showed that the stone was capable of wearing away iron.  But in vain did he try to twist his legs so as to rub the rivet against the wall, and he gave up the attempt as impossible.

It was clear, then, that he must have a bit of the stone to rub with.  He at once began to dig with the dagger in the earth at the foot of the wall, to see if he could find any such pieces.  For a long time he came across no chips, even of the smallest size.  As he worked, he was most careful to stamp down the earth which he had moved, scattering over it the sand, of which there was an abundance in the corners of the room, to obliterate all traces of his work.