But the least use of explosives is in war; not over ten per cent is so used. The Mont Cenis tunnel took enough for 200,000,000 musket cartridges. As much as 2,000 kegs have been fired at once in California to loosen up gravel for mining, and 23 tons were exploded at once under Hell Gate, at New York. How strong is this gas? As strong as you please. Steam is sometimes worked at a pressure of 400 pounds to the inch, but not usually over 100 pounds. It would be no use to turn steam into a hole drilled in rock. The ordinary pressure of exploded gas is 80,000 pounds to the square inch. It can be made many times more forceful. It works as well in water, under the sea, or makes earthquakes in oil wells 2,000 feet deep, as under mountains. The wildest imagination of Scheherezade never dreamed in _Arabian Nights_ of genii that had a tithe of the power of these real forces. Her genii shut up in bottles had to wait centuries for some fisherman to let them out. NATURAL AFFECTION OF METALS "Sacra fames auri." The hunger for gold, which in men is called accursed, in metals is justly called sacred. In all the water of the sea there is gold--about 400 tons in a cubic mile--in very much of the soil, some in all Philadelphia clay, in the Pactolian sands of every river where Midas has bathed, and in many rocks of the earth. But it is so fine and so mixed with other substances that in many cases it cannot be seen. Look at the ore from a mine that is giving its owners millions of dollars. Not a speck of gold can be seen. How can it be secured? Set a trap for it. Put down something that has an affinity--voracious appetite, unslakable thirst, metallic affection--for gold, and they will come together. We have heard of potable gold--"_potabile aurum_." There are metals to which all gold is drinkable. Mercury is one of them. Cut transverse channels, or nail little cleats across a wooden chute for carrying water. Put mercury in the grooves or before the cleats, and shovel auriferous gravel and sand into the rushing water. The mercury will bibulously drink into itself all the fine invisible gold, while the unaffectionate sand goes on, bereaved of its wealth. Put gold-bearing quartz under an upright log shod with iron. Lift and drop the log a few hundred times on the rock, until it is crushed so fine that it flows over the edge of the trough with constantly going water, and an amalgam of mercury spread over the inclined way down which the endusted water flows will drink up all the gold by force of natural affection therefor. Neither can the gold be seen in the mercury. But it is there. Squeeze the mercury through chamois skin. An amalgam, mostly gold, refuses to go through. Or apply heat. The mercury flies away as vapor and the gold remains. If thou seekest for wisdom as for silver, and searchest for her as for hid treasure, thou shalt find. NATURAL AFFECTION BETWEEN METAL AND LIQUID