276 LOGGING 



larger cavity may be made for the powder. Dynamite of 40 

 per cent strength is used for "springing," about 2V of a pound 

 per cubic yard being fired in shale, and tV 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 i pound per cubic yard have 

 proved successful in side cuts and from i| 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- or 50-pound cans and costs from 

 6 to 9 cents per pound. 



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 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 always be placed immediately 

 under the stump but not in it, and as near as possible to its 

 toughest part. 



In sandy soil 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 near 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. 



1 See "Handbook of Cost Data," by H. B. Gillette. Myron C. Clark Publish- 

 ing Company, Chicago, 111., 1910. P. 204. 



