Before I did anything more in the way of manufacture, I paid another visit to the isthmus, and selected the site for the mine which was to tear an opening in it. I found a deep crevice in the rocks, and spent many weeks in clearing and enlarging it, until I had ready a chamber deep in the heart of the barrier, below the level of the lake. During all that time I lived upon the little fruits and upon the flesh of the sloths I killed. I carefully saved the fat from the latter, saponified it with alkalies leached from wood ashes, and removed the soap by "salting down" with evaporated brine from a salt spring. I collected and stored the glycerine until I had many gallons. At last, judging that my "nitrate plantation" had had time to serve its purpose, I dug it up, leached the product, and crystallized the saltpeter by evaporation in earthen pots. The yield was satisfactory in quantity and fair in quality, but it had cost fearful effort. Then I set about the manufacture of sulphuric acid by roasting the iron pyrites with nitrate in my crude apparatus, collecting the acid in wet pottery condensers. That took many days, and the next step was making nitric acid by boiling saltpeter in sulphuric acid and condensing the fumes. At last, when I had the three necessary chemicals--glycerine, and nitric and sulphuric acids--I set out to transport them separately to my mine, to avoid the hazard of the transportation of the finished product. That, again, was a heart-breaking task, for I had materials enough to make several hundred quarts of nitroglycerine, and the distance was half a dozen miles. But ragged, ill-kept savage that I was, I had collected on the cliffs above my shaft the materials for the manufacture of a good quantity of high explosive. For one in my position, it had been a considerable achievement. CHAPTER XXXI The Mine on the Brink At last, in haste and fear and trembling, I began the task of mixing my chemicals, dumping them into vats of water cooled by evaporation, under a rude shed to cut off the fierce heat of the red sky. Even with all my precautions to prevent a premature explosion, the hazard was fearful. I washed the nitroglycerine, and carried it in earthen jars down into the heart of the cliffs. I meant to die in the final explosion, but I was afraid the stuff would go off before it was in place. But finally I got the last of the rough jars into position. Then I closed the mouth of the chamber with rocks and rubbish, to be sure that the full force of the explosion would be exerted upon the cliff. I lit the fuse I had prepared--a tall candle of the sloth's fat, which, burning low, would ignite a powder train; and that would set off a charge of gunpowder I had placed by the jars of nitroglycerine.