RAILROAD CONSTRUCTION 311 
Moist clay is the most satisfactory tamping material, 2 or 3 
inches of dry earth being placed over the powder to prevent the 
upper end of the charge from becoming moist. 
When blasting with black powder the holes may be "sprung" 
with dynamite before the powder is inserted, in order that a 
larger cavity may be made for the powder. Dynamite of 40 
per cent strength is used for "springing," about ^V o^ ^ pound 
per cubic yard being fired in shale, and ^^ of a pound per cubic 
yard in sandstone. "Sprung" holes should not be charged until 
they have become cool. 
The amount of black powder required per cubic yard of material 
to be blasted is governed by the depth of hole, character of 
rock, and spacing of holes. Authorities on the use of black 
powder do not attempt to give any rules for determining the 
amount of charge. Charges of 1 pound per cubic yard have 
proved successful in side cuts and from 1^ to 3 pounds per cubic 
yard in through cuts.^ The amount to use under given condi- 
tions can be determined only after a few trial shots. 
Black powder is put up in 25- and 50-pound cans. 
STUMP BLASTING 
The removal of stumps from the right-of-way of roads, trails, 
logging grades, and from pond and building sites can often be 
accomplished to best advantage by the use of explosives. Dyna- 
mite of the 20, 40 and 60 per cent grades is preferable to black 
powder for this purpose. 
The position of the blast with reference to the stump should 
be governed by the size of stump, character of root system, and 
kind of soil. Charges should be placed under the main body 
of the stump, and as near as possible to its toughest part. 
In sandy soils, stumps with a shallow root system require more 
explosive than those with tap roots. They blast easier in heavy 
and moist soils than in light or dry ones. 
For blasting yellow pine stumps with long tap roots the charge 
should be placed in the tap root and at a distance under ground 
at least equal to the diameter of the stump. Forty per cent 
dynamite is usually preferred. 
Cypress stumps have many lateral roots and since they usually 
1 See "Handbook of Cost Data," by H. B. Gillette, p. 204. 
