RAILROAD CONSTRUCTION 
309 
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There are two methods of inserting the cap into the primer. 
A common method (Fig. 100a) is to open the paper at the end 
of a cartridge, and, with a sharpened stick about the size of a 
lead pencil, make a hole f-inch deep in the dynamite. The cap, 
with fuse attached, is then inserted in this cavity and should 
project |-inch above the dynamite, otherwise the sputtering of 
the fuse may ignite the dynamite^ before it does the cap. The 
cartridge paper is then tied around the fuse with a string, care 
being taken not to pull the cap out of the primer. If the car- 
tridges are used in wet places soap or tallow is smeared over 
the safety fuse at the point where it enters the cartridge to pre- 
vent the entrance of moisture into the 
blasting cap. 
Some persons prefer to use the 
method of attaching caps shown in Fig. 
1006. A hole is punched in the side of 
the cartridge with a sharp wooden stick 
and the fuse attached as shown. This 
method is satisfactory because the fuse 
comes against the side of the bore and 
is not injured or disturbed by the 
tamping bar, and the cap cannot be 
pulled from the primer and thus cause 
a misfire. 
Primers are placed on top of the 
charge, but in deep holes, manufac- 
turers recommend that additional 
blasting caps without fuse be placed at 
5-foot intervals throughout the charge. 
Electric Fuse. — When it is desired to fire several difTerent 
charges at one time electric fuses are used in connection with a 
battery. They consist of two wires inserted in a cap containing 
a mixture of fulminate of mercury and potassium nitrate or 
chlorate. The open end of the cap is plugged with sulphur. 
The fuses are adjusted as shown in Fig. 100c. When an electirc 
fuse is used the primer is placed in the center of the charge. 
The practice in electric firing is to separate the two wires on the 
fuse and connect one to a wire on a charge on one side and the 
other to one on a charge on the opposite side. The entire set 
is connected up in this manner leaving one free wire extending 
d e 
Fig. 100. — Method of plac- 
ing Caps in the Primer, 
a, and b, are for firing with 
safety fuse, c, for firing 
with an electric battery. 
d, shows the cap ready for 
the insertion of the fuse. 
e, cap with fuse inserted 
and the cap shell crimped. 
