The fire is communicated to the mines by a pipe or hose, made of coarse cloth, whose diameter is about one and a half inch, called a saucisson, (for the filling of which near half a pound of powder is allowed to every foot) extending from the chamber to the entrance of the gallery, to the end of which is fixed a match, that the miner who sets fire to it may have time to retire, before it reaches the chamber.
To prevent the powder from contracting any dampness, the saucisson is laid in a small trough, called an auget made of boards, three and a half inch broad, joined together, lengthwise, with straw in it, and round the saucisson, with a wooden cover nailed upon it.
Foyer, Fr. Focus or centre of the chamber, some authors call the end of the saucisson that comes within the work, and which is to be set fire to, the foyer, or focus: but by most people, this is generally understood to be the centre of the chamber.
Galleries and chambers of Mines. Galleries made within the fortification, before the place is attacked, and from which several branches are carried to different places, are generally 4 or 4¹⁄₂ feet wide, and 5 or 5¹⁄₂ feet high. The earth is supported from falling in by arches and walls, as they are to remain for a considerable time; but when mines are made to be used in a short time, then the galleries are but 3 or 3¹⁄₂ feet wide, and 5 feet high, and the earth is supported by wooden frames or props.
The gallery being carried on to the place where the powder is to be lodged, the miners make the chamber. This is generally of a cubical form, large enough to hold the wooden box, which contains the powder necessary for the charge: the box is lined with straw and sand-bags, to prevent the powder from contracting dampness.
The chamber is sunk something lower than the gallery, if the soil permits; but where water is to be apprehended, it must be made higher than the gallery; otherwise the besieged will let in the water, and spoil the mine.
Quantities of powder to charge, Mines. Before any calculation can be made of the proper charge for a mine, the density and tenacity of the soil in which it is to be made, must be ascertained, either by experiment, or otherwise; for, in soils of the same density, that which has the greatest tenacity, will require the greatest force to separate its parts. The density is determined by weighing a cubic foot (or any certain quantity) of the soil; but the tenacity can only be determined by making a mine. The following table contains experiments in 6 different soils, which may be of some assistance to form a judgment of the nature of the soil, when an actual experiment cannot be had.
| Nature of the soil. | Density. | Tenacity. | ||||
|---|---|---|---|---|---|---|
| Weight of 1 cubic foot. | Quantity of power to raise 1 cubic fathom. | |||||
| 1. | Loose earth or sand | 95 | pds. | 8 | pds. | |
| 2. | Common light soil | 124 | 10 | |||
| 3. | Loam, or strong soil | 127 | 12 | ¹⁄₄ | ||
| 4. | Potter’s clay, or stiff soil | 135 | 13 | ¹⁄₂ | ||
| 5. | Clay, mixed with stones | 160 | 16 | |||
| 6. | Masonry | 205 | 21 | ¹⁄₂ | ||
All the requisites in mining may be determined by the following problems, which admit of 4 cases; for any 3 of the articles below being given, the 4th may thence be found.
1. The nature of the soil,