I hadn't been a mining engineer for nothing, and I knew lentonite when I saw it.
With one of these bricks I could blow the house to smithereens.

I had used the stuff in Rhodesia and knew its power.

But the trouble was that my knowledge wasn't exact.

I had forgotten the proper charge and the right way of preparing it, and I wasn't sure about the timing.

I had only a vague notion, too, as to its power, for though I had used it I had not handled it with my own fingers.
But it was a chance, the only possible chance.