The _needle_ is a smooth copper wire, longer than the depth of the hole. It has a ring handle, by which it may be turned around and withdrawn. It is inserted in the charge, the tamping is well rammed around it, and it is withdrawn, leaving a pipe in the tamping, through which fire may be communicated, as described for the firing-tube. =98. Tamping.=--The best and safest tamping is perfectly dry silicious sand, poured in the hole so as to fill it completely, but not rammed. It cannot be used in holes which incline upward nor when the needle is used. In such cases moist clay, brick-dust, etc., are used. The first layers are pressed in upon the charge, and the subsequent ones thoroughly rammed down with a copper tamping-bar. A hammer is used with the bar, when necessary, in deep holes and hard rock. _With high explosives no tamping should be used except dry sand or water. Holes which incline upwards should receive an extra charge and be untamped._ =99. Determining the Charge.=--The charge of gunpowder or high explosive required for any particular hole in ordinary blasting can be best estimated by an experienced blaster. If one is not to be obtained, an approximate estimate for the first experiment may be made from the formulas (counting the high explosives about four or five times as strong as gunpowder for ordinary use), and the charges for subsequent blasts may be estimated from the effects of those first fired. =100. Precautions.=--If a _tamped_ hole misses fire _it should never be cleared out for recharging_. A new hole should be drilled near, but not breaking into it. Electric fuses or Bickford fuses (with blasting-caps for high explosives) should always be used when they can be obtained. DEMOLITIONS. =101. Deliberate Demolitions=, such as the destruction of walls, casemates, etc., in time of peace, or at a distance from the enemy in time of war, should be so made as to economize powder and work. To accomplish this, the mines and blasts should be located where they will produce the best effects attainable, and the charges should be proportioned to the work required from them. The table previously given (p. 124) will serve as a guide for computing the first charges used, and from the results of these the charges of subsequent ones may be determined. Judgment must be used in placing the charges, so that, when possible, they will destroy the supports and allow the superstructure to break up by falling. The charges will usually be placed in chambers under or hollowed out in the masonry. Sometimes they are more advantageously placed in a trench outside and close to the foot of the walls. They should always be well tamped: when in mine-chambers, by methods previously described; when in trenches, or laid along the exterior of walls, by loading them with earth, etc., until the line of least resistance passes through the wall to be destroyed. =102. Hasty Demolitions= are made when the time available for the work is limited.