Portfires are of four different natures—viz., Common portfires, Percussion portfires, Miners’ portfires, and Slow portfires.
A common portfire is 16 inches long, and will burn 15 minutes.
| Composition. | |
| lb. | |
| Brimstone, sublimed | 2 |
| Powder, cylinder mealed | 1 |
| Saltpetre, pulverized | 6 |
PORTFIRES, PERCUSSION.
| Composition. | |
| Brimstone, sublimed | 4 |
| Powder, cylinder mealed | 1 |
| Saltpetre, pulverized | 8 |
The percussion priming is added to these portfires at the stations where they are used (principally for the Coast Guard), and is simply a small glass globule, containing sulphuric acid. This is embedded in loose composition, which ignites on the globule being broken. A percussion portfire will burn 5 minutes.
PORTFIRES, MINERS.
| Composition. | ||
| lb. | oz. | |
| Saltpetre, pulverized | 0 | 8 |
| Sulphur, sublimed | 0 | 8 |
| Powder, cylinder mealed | 1 | 0 |
PORTFIRES, SLOW.
The paper, which is called blue sugar-loaf paper, is wetted by dissolving 12 ounces of saltpetre in one gallon of water, wetting each sheet separately on both sides with a brush, one side being dried before the other is made wet.