310 LOGGING 
both from the first a d the last hole. The two leading wires, 250 
feet or more in length, are then connected to the above wires and 
carried to some protected point. When all is in readiness the 
leading wires are attached to the poles of the battery and the 
charge fired by an electric firing machine. 
Tamping. — Tamping should always be done with a wooden 
bar, never with a tool having any metal parts, and the tamping 
material must be free from all forms of grit, and of such a nature 
that it will pack firmly. The most satisfactory is moist clay or 
loam. 
After the charge has been pressed tightly in the bore a paper 
wad may be placed over the primer to keep it dry and from 2 
to 3 inches of tamping material put in and firmly, but gently, 
packed. Two or 3 inches more of tamping material are again 
added and throughly tamped. After 5 or 6 inches of earth 
have been placed in the bore the tamping can be carried on 
without fear of premature explosion. The hole should be filled 
to the surface and the material tightly packed, or it will blow out 
and much of the force of the explosive will be lost. 
Low Explosives. — Low explosives belong to either the soda or 
the saltpeter class and are known as black powder. The average 
contain approximately 75 per cent of nitrate of soda, or India 
saltpeter, 10 per cent of sulphur, and 15 per cent of carbon. 
Dynamite of 75 per cent strength is usually rated as six times 
stronger than average black powder. Soda powders can be made 
cheaper than saltpeter pow^ders but are more absorbent of moisture 
and, therefore, deteriorate quicker. 
Black powder is especially suited for loosening hardpan, shale, 
and other soft or rotten rock where a lifting action is desired. 
It is much slower than high-grade djmamite and does not shatter 
the rock as much. It is also used in redwood operations to 
blast open logs that are too large to be handled by available 
equipment. 
Black powder is fired by a safety fuse, by a safety fuse and a 
cap of low power, or by an electric fuse. In loading holes the 
powder may be placed loose or in cartridges. When the holes 
open downward the latter form is the only method possible. 
In priming holes it is customary to place the safety fuse or 
safety fuse and cap at the top of the charge while electric fuses 
are ordinarily placed in the center of the charge. 
