NITRO-GLYCERINE EXPLOSIONS.
The nine charges are fired simultaneously by means of electricity. The double wire, insulated with gutta-percha, extends into a small cartridge of powder, which is placed in the top of each charge of nitro-glycerine. The ends of the wire are brought quite near each other, and between them a small slip of platinum is soldered. The current of electricity, passing through the wires, heats this platinum to redness, and sets fire to the powder around it. The powder explodes, and its explosion sets fire to the nitro-glycerine. As the battery which furnishes the electricity is on board the boat, the current is thrown into each pair of wires simultaneously and thus the explosions occur at exactly the same moment.
A column of water shoots up into the air, the rock is torn and broken, and there is a general disturbance of the water all round it: ships and boats are warned, by means of a red flag, to keep at a safe distance. It generally happens that a good many fishes that have been swimming around the rock at the time of the explosion are killed, and rise to the surface; those that are not killed are very much astonished, and swim away with great rapidity.
The experience of a diver going down to arrange the charges is not highly agreeable. If he remains longer than the period of slack water, he finds the current so strong that it almost carries him off his feet; and it frequently becomes necessary for him to be drawn to the surface and abandon his work until the next turn of the tide. Should an explosion occur while he is below, it would be pretty certain to cause his death.
The substance which he handles is not the safest in the world, but the engineers seem to be agreed that it is much better in every way than gunpowder. They say that accidents which have occurred from the use of nitro-glycerine have been caused by careless or ignorant handling, and that many accidents to which powder is liable will not occur with nitro-glycerine.
General Newton explained to us that a few days before our visit a slight accident occurred, which would have proved fatal had they been using powder. At that time they were using fulminating caps instead of electricity; one of the fulminating caps was ignited, and set fire to the charge of powder: the case was broken and the nitro-glycerine was spilled about, but nothing serious happened. Had they been using gunpowder instead, the consequences would have been fatal.
EFFECTS OF NITRO-GLYCERINE.
In nearly all the modern blasting operations in the United States, in Europe, and in many other places, nitro-glycerine takes the place of powder; it is much more powerful in its effect, a single charge of it breaking and shattering a rock much more than gunpowder. It has the advantage, too, of extending its force completely to the bottom of the hole, whereas gunpowder very frequently acts only part way down the hole.
My individual experience of nitro-glycerine has not been of the most pleasing character. In 1866 I sailed from New York for San Francisco by way of Panama; when we reached Aspinwall we crossed the Isthmus to take the Pacific steamer at Panama. It was nearly sunset when we climbed up the gangway, and stood upon her deck; an hour later, the tug with our baggage, and with the express freight and mails, came out. I was standing near the gangway when the baggage and express matter came on board, and I think, though I will not be positive about it,—and some of my acquaintances say it is very unlikely,—that I assisted in taking a few of the boxes over the rail. Everything was stowed away, and about ten o’clock at night we steamed down the Bay of Panama, and were on our way to San Francisco. We reached the latter city in safety on a Saturday morning, and I was introduced to a very large number of gentlemen, and most hospitably entertained.