Each of these holes is then charged with a half cartridge of 

 20 per cent Red Cross Dynamite, which has previously been primed 

 with a No. 6 Du Pont cap crimped on to about three feet of fuse, the 

 length of the fuse required being enough to reach to the top of the 

 ground. Each hole must then be tamped with a wooden tamping stick, 

 using moist earth or clay for this purpose. The tamping must be done 

 thoroughly, as the object of the blast is to crack and shake up the subsoil 

 sideways and downwards rather than to blow the subsoil up into the 

 air. For this reason, subsoiling should be done only when the ground 

 is dry, because when it is wet the blast is almost certain to blow up- 

 wards and make a hole in the ground instead of breaking it up side- 

 ivays. 



After a considerable number of holes have been charged the blaster 

 passes from one hole to another, lighting the fuses; the explosions 

 follow about one minute after the fuse is lit. As the charge is usually 

 effective principally underground it is not necessary for the blaster to 

 keep any great distance away from the explosions. 



Firing the charges electrically has advantages, the chief of which 

 is that all the blasts over a large area covered by twenty or thirty 

 holes may be fired at one time and the shaking and cracking effect of 

 the various charges is greater because of this united action. This method 

 is, however, more expensive. 



Another advantage is that there is much less liability of a misfire, 

 which may occur when the cap and fuse method is used, because the 

 cap may pull out of the cartridge after it is lowered into the hole. 

 This seldom happens when an electric fuze is used. 



Detailed instructions for preparing and loading subsoil charges for 

 both methods of blasting will be found on pages 119 to 126. 



Method of Breaking Up Hardpan: 



A large part of the farms of this country are underlaid with a 

 natural hardpan of clay which is completely impervious to water 

 and which lies from ten to forty inches beneath the surface. Such 

 a hardpan is a constant menace to crops. It prevents the storage of 

 moisture and causes the topsoil to wash away in wet weather and 

 dry out quickly in dry weather. Where the ground is level such a 

 hardpan will cause pools of water to form in fields in wet weather 

 which drowns out the vegetation. This hardpan must be broken be- 

 fore good crops can be raised on such land. 



When subsoiling under such conditions the exact location of the 

 charge must be determined by the depth of the hardpan. The holes 

 should be placed so that the cartridge is imbedded in the hardpan. 

 When the hardpan is very near the surface the holes should be about 

 thirty inches in depth, but if the hardpan is very tough the holes 

 should not be as far apart as fifteen feet. It is rarely necessary to put 

 them closer than ten feet. 



Where the top of the hardpan is from thirty to forty inches below 

 the surface it is necessary to bore the holes deeper so as to locate the 

 cartridge in the hardpan. With the hardpan reaching to within thirty 

 inches of the surface, for instance, and a charge placed in a thirty-six 



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