He made a cartridge about three times the size of those they used in the rock. Jim Bently said it was big enough to blow the bottom out of the river. The inner skin was of stout calico; Andy stuck the end of a six-foot piece of fuse well down in the powder and bound the mouth of the bag firmly to it with whipcord. The idea was to sink the cartridge in the water with the open end of the fuse attached to a float on the surface, ready for lighting. Andy dipped the cartridge in melted bees’-wax to make it water-tight. ‘We’ll have to leave it some time before we light it,’ said Dave, ‘to give the fish time to get over their scare when we put it in, and come nosing round again; so we’ll want it well water-tight.’
Round the cartridge Andy, at Dave’s suggestion, bound a strip of sail canvas—that they used for making water-bags—to increase the force of the explosion, and round that he pasted layers of stiff brown paper—on the plan of the sort of fireworks we called ‘gun-crackers’. He let the paper dry in the sun, then he sewed a covering of two thicknesses of canvas over it, and bound the thing from end to end with stout fishing-line. Dave’s schemes were elaborate, and he often worked his inventions out to nothing. The cartridge was rigid and solid enough now—a formidable bomb; but Andy and Dave wanted to be sure. Andy sewed on another layer of canvas, dipped the cartridge in melted tallow, twisted a length of fencing-wire round it as an afterthought, dipped it in tallow again, and stood it carefully against a tent-peg, where he’d know where to find it, and wound the fuse loosely round it. Then he went to the camp-fire to try some potatoes which were boiling in their jackets in a billy, and to see about frying some chops for dinner. Dave and Jim were at work in the claim that morning.