354 Apparatus for Rock Blasting. 
the powder, the brickdust, or sand, or other matter, employed to 
close it. | 
Sd. 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 J have resorted, 
are as follows :— my 
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. 
