140 Application of Galvanic Ignition in Rock Blasting. 



These remarks have reference tq the principal and highly impor- 

 tant object of Mr. Shaw's project ; which is, to ignite at once a great 

 number of charges in ag many perforations so drilled in a rock as to 

 co-operate simultaneously in the same plane. By these means it is 

 conceived that the stone may be separated into large prismatic or tab- 

 ular masses, instead of being reduced to irregular fragments of an in- 

 ferior size. The object to v»^hich I propose now to call attention 

 more particularly is a modification of the common process of blast- 

 ing by one charge, which renders that process perfectly safe. 



This part of the subject I shall introduce by premising that almost 

 all the accidents, which have taken place in blasting rocks, have oc- 

 curred in one of the three following modes : 



1st. The explosion has taken place prematurely, before the opera- 

 tor has had time to retire. 



2nd. A premature explosion has ensued from a spark produced 

 by the collision arising from ramming into the orifice of the perfora- 

 tion, containing the powder, the brick dust or sand employed to 

 close it. 



3rd. 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, lately published. 



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 firm- 

 ly 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 render- 

 ed the sole mean of metallic connection betvv^een the larger ones. 

 These are tied in a saw kerf, so made in a small piece of dog wood, 

 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 per- 

 foration in the rock to such a height as may be deemed proper. This 

 tube being supplied with gun powder, the orifice is closed with a cork, 

 perforated so that the twisted wire may pass out through it without 



