354 Apparatus for Rock Blasting. 



, the powder, the brickdust, or sand, or other matter, employed to 

 close it. 



3d. The fire not reaching the charge after the expiration of a pe- 

 riod unusually long, and the operator returning to ascertain the cause 

 of the supposed failure, an explosion ensues when he is so near as to 

 suffer by it, as in the instance near Norristown, published some years 



ago. 



The means of communicating ignition, to which I have resorted^ 

 are as follows : 



Three iron wires, of which one is of the smallest size used for wire 

 gauze, the others of the size (No. 24,) used by bottlers, are firmly 

 twisted together. This is best accomplished by attaching them to 

 the centre of the mandril of a lathe, which is made to revolve while 

 the other ends of the wires are held by a vice, so as to keep them in 

 a proper state of tension. After being thus twisted, a small portion 

 is untwisted, so as to get at and divide the larger wires by means of 

 a pair of nippers. In this way the smaller wire is rendered the sole 

 mean of metallic connexion between the larger ones. These are tied 

 in a saw kerf, so made in a small piece of dogwood as to secure them 

 from working, which, if permitted, would cause the smaller wire to 

 break apart. At one end, the twist formed of the wires is soldered 

 to the bottom of a tin tube of a size to fill the perforation in the rock 

 to such a height as may be deemed proper. This tube being supplied 

 with gunpowder, the orifice is closed with a cork, perforated so that 

 the twisted wire may pass out through it without touching the tube at 

 any point above that where the finer portion alone intervenes. To the 

 outside of the tube, a copper wire, about No. 16, is soldered, long 

 enough to extend to a stout copper wire proceeding from one of the 

 poles of a galvanic deflagrator or calorimotor. The wire passing 

 through the cork from the inside of the tube, is in like manner made 

 to communicate with the other pole. The connexions between the 

 wires and the poles, should be made by means of soft solder, previ- 

 ously to which we must imagine that the tube has been introduced 

 into a perforation made for its reception in a rock to be blasted. The 

 tin tube may be secured within the rock by the usual method of ram- 

 ming in brickdust or sand, by means of a plug, having holes for the 

 protection of the wires of communication already described.'* 



* It has occurred to me that plaster of Paris might be used advantageously, as it 

 would require no ramming, and might set with sufficient firmness. 



