There was a box of detonators, and a lot of cord for fuses.

Then away at the back of the shelf I found a stout brown cardboard box, and inside it a wooden case.

I managed to wrench it open, and within lay half a dozen little grey bricks, each a couple of inches square.
I took up one, and found that it crumbled easily in my hand.

Then I smelt it and put my tongue to it.

After that I sat down to think.