Harper's Round Table, June 9, 1896

by Various

In another mill the saltpetre is refined by boiling. The refined product is dumped into vats, from which it is shovelled into barrels to be taken to the mixing-house. The saltpetre in the vats is so pure and white that one might fancy that the roof had opened and an old-fashioned snow-storm had fallen inside the building, and the men who are shovelling it up resemble snow-shovellers, except that they are not bundled up. The sulphur is prepared in another place, and then the ingredients are taken to the mixing-mill, where they are weighed and mixed, and there the part of the work that is not dangerous ends.

THE ROLLING-MILL.

Near by the mixing-mill are the rolling-mills. Now we are close to danger. In the centre of this mill is a big iron saucer, probably six feet in diameter. The rim of the saucer is about eighteen inches high. Standing up in the saucer are two wheels. They seem to be about six feet in diameter also, and their rims about a foot broad. These wheels and this saucer do the rolling of the powder—that is, they grind the three substances that compose the powder into a new mixture. The wheels are swept around and around in the saucer, and they also turn on their own axes. It is as if they were kept rolling over and over, just as the wheels of a carriage roll, but also as if some power kept them turning about constantly in the small circle of this saucer. This mill is where wooden machinery cannot be used, and of course that makes it a very dangerous place.

The mixture of the ingredients of the powder is brought in and dumped carefully in the saucer. It is spread about smoothly by a workman, who, after this work is done, goes outside the mill, and does not come back until the powder is rolled thoroughly. The workman goes to a wheel a few feet away from the building and turns it very slowly. It starts the machinery that moves the wheels in the saucer. The greatest danger in rolling comes at this time. The rolling must be begun in the slowest possible way. The danger is that there may be a lump in the mixture in the saucer that will raise one of the wheels as it turns around and then drop it suddenly in the saucer, causing a spark. If this comes, away goes your mill and machinery, and possibly the workman's life with them. There are many of these rolling-mills in the Du Pont plant, because the owners act on the principle that it is not a good thing to carry all your eggs in one basket. Rarely is more than 150 pounds of powder rolled at one time, and it takes from three to eight hours to do the rolling, according to the grade of powder that is being made. The workman in charge will go to the door of the mill from time to time to look in, but he never steps inside until he has stopped the machinery and the rolling is done.

After the powder is rolled it is shovelled up and taken to a press-mill. It is put into a long wooden trough about two feet high and two feet broad, and packed between thin plates of aluminum. Pressure is applied by water-power to one end of the trough, and the powder is squeezed into thin slabs of hard dry cakes. After all the moisture is squeezed out, these cakes are removed, and one by one they are slipped down into a slot between some rollers, where each is broken up into bits that resemble the small stones that are used in making macadam roads. This breaking-up process makes a terrific noise, and when one thinks of the dangerous compound that is being handled, this noise is likely to cause a feeling of great fear in one who hears it for the first time. At this stage of the process it is difficult to restrain the impulse to take to one's heels and run out of hearing of the terrifying sound.

THE GRAINING-MILL.

After the cakes have been broken up into these bits of rough, dirty stone, the powder is taken to a graining-mill. This is really the most dangerous part of all the work. One man runs each of these mills. He cannot start the machinery in motion and go away, like the man who has charge of a rolling-mill, but he must stay in the place all the time, and feed the stones to the machinery that crushes them into grains of various sizes. He shovels the powder into a large hopper, big wooden wheels go around and around, and the powder passes between zinc rolls and through sieves of various sizes. It is a grewsome place. The machinery reminds one of the pictures that we have all seen of some of the contrivances they used to have in the days of the Inquisition with which to torture people, and it is hard to keep back a shudder as one looks at this work. Sometimes there is as much as a ton of powder at one time in the big hopper of this machine. In one of these mills at the Du Pont Works you will notice that the stone wall is eight feet thick on one side. This is on the side next to a press-mill. One side of the place is entirely of wood. This is toward the creek. The idea is to save as much property as possible in case of an explosion.

After the powder is broken up into grains it is taken in bags to another mill. This is known as a glazing-mill. It is here that the powder is polished and made shiny. There are several sheet-iron hoppers that resemble enormous barrels in this place. The powder is dumped into them, and they are turned over and over. A certain quantity of lamp-black is put into each barrel, according to the amount of powder each contains, and the barrel is turned until every grain has received a polish. The polish simply gives the powder a nice appearance. It adds no strength to the product, but it helps to keep out moisture, and it prevents the powder from losing some of its strength in damp weather. Every one knows how much better a pair of shoes look when they are polished, and how desirable it is at all times to have one's shoes kept in this condition. It is for that same reason that a polish is put on the grains of powder.