s 



BULLETIN 91, U. S. DEPARTMENT OF AGRICULTURE. 



that the propulsive or lifting force of 60 per cent "straight" nitro- 

 glycerin dynamite is only 18.7 per cent more than that with 30 per 

 cent. On the other hand, its disruptive or shattering force is 42.5 

 per cent more. Carefully conducted field tests in stump blasting 

 have shown that the propulsive or lifting effect of 40 per cent nitro- 

 glycerin dynamite is but little more than that of 20 per cent, while 

 the disruptive or shattering effect of the 40 per cent is considerably 

 more than that of the 20 per cent preparation. In stump blasting a 

 high propulsive force and a comparatively low disruptive effect are 

 desirable. For this reason ammonia dynamite (powders containing 

 some ammonia and branded "extra") and powders containing no 

 nitroglycerin, because of their slower action and consequent low 



Fig. 5. — Capstan stump puller. This type requires an anchor stump from which all stumps within 

 a radius equal to the length of the pulling cable can be pulled. 



disruptive effect, are generally to be preferred to the straight nitro- 

 glycerin powders. In case the lower nitroglycerin powders or their 

 equivalent are employed, No. 6 or stronger caps should be used. 



STUMP PULLERS. 



Two types of stump pullers are used — those that pull from the side, 

 as the capstan (fig. 5), and the tripod type, which lifts the stump 

 vertically (figs. 6 and 7). 



THE CAPSTAN TYPE OF MACHINE. 



The capstan type has the advantage that an acre or more of stumps 

 can be pulled at a single setting. In pulling small stumps like scrub 

 oak, j;iek pine, and certain kinds of hardwood, the saving in time is 



