CLEARING LAISTD IN THE LAKE STATES. 7 



In cultivating a field covered with stumps, it is impossible to use 

 modern farm machinery efficiently. Stumps are removed (1) by 

 explosives alone, (2) by explosives used in connection with stump 

 pullers or block and line, (3) by stump pullers alone, and (4) by 

 power machines. 



EXPLOSIVES. 



Explosives alone are used effectively and economically in all stump- 

 ing operations on the heavier soils and for well-decayed hardwood 

 stumps on the lighter soils. , They have the advantages of thor- 

 oughly breaking up the stumps, of not requiring a large force of men 

 for clearing operations or a large cash outlay at one time, and of 

 enabling the work to be done quickly. The rather high cost of 

 explosives when bought in small quantities and the fact that only 

 experienced men should handle them are their chief drawbacks. 

 Direct cooperative buying in wholesale lots will reduce materially the 

 cost of the explosives. 



Satisfactory instructions 1 regarding the use of explosives are now 

 published by practically all manufacturers. The chief faults of the 

 average man in blasting stumps are his tendency to place the charge 

 too shallow and his failure to put it under the center of resistance of 

 the stump. 



On most of the land-clearing operations in Michigan dynamite 

 containing 40 per cent of nitroglycerin or its equivalent is used. In 

 a few sections dynamite containing 20 to 30 per cent of nitroglycerin 

 or its equivalent has been used with very satisfactory results. On 

 the Pacific coast 20 per cent nitroglycerin dynamite or its equivalent 

 is used almost exclusively. Dynamite containing the smaller per- 

 centages is cheaper, less dangerous to use, and does not pack the soil 

 to such an extent as the stronger preparations. On the heavier soils 

 the lower strength explosives will give just as good results pound for 

 pound as the higher. The lower strengths act more slowly, with 

 much less shattering, and have almost the same lifting force as those 

 containing higher percentages of nitroglycerin. 



It is commonly believed that dynamite with 60 per cent of nitro- 

 glycerin is twice as effective as that with 30 per cent and that that with 

 40 per cent of nitroglycerin has twice the effectiveness of 20 per cent. 

 Tests by the United States Bureau of Mines 2 have demonstrated 



1 Valuable information regarding the proper use of explosives in stumping ma}' be found in the following 

 publications: 



McGuire, A. J. Land clearing. University of Minnesota Agricultural Experiment Station, Bulletin 

 134, 32 p., 21 fig., 1913. 



Kadonsky, J. F. The use of explosives in clearing land. University of Wisconsin Agricultural Experi- 

 ment Station, Bulletin 216, 19 p., 20 fig., 1911. 



Thompson, Harry. Cost and methods of clearing land in western Washington. L T . S. Department of 

 Agriculture, Bureau of Plant Industry, Bulletin 239, 60 p., 25 fig., 1912. 



2 Hall, Clarence, and Howell, Spencer P. The selection of explosives used in engineering and mining 

 operations. U. S. Department of the Interior, Bureau of Mines, Bulletin 4S, 50 p., 3 pi., 7 fig., 1913. 



