METHODS OP TESTING EXPLOSIVES MUNROE. 295 



The pendulum consists of a 12.2-inch Army mortar, weigliing 

 31,000 pounds, which rests in a stirrup made of two 1^-inch machine- 

 steel rods bent in a U shape. The ends of these rods pass through a 

 solid-steel supporting beam and are held fast to it by cast-steel 

 saddles fitting over the beam. This beam is provided with two 

 nickel-steel knife-edges countersunk in its loAver face, which rests on 

 bearing plates provided with small groves that permit of the knife- 

 edges being kept in oil, so as to be protected from the weather. The 

 bearing plates rest on base plates which are anchored to the concrete 

 piers between which the pendulum mortar swings. 



The concrete piers are each 51 by 120 inches in dimension at their 

 bases and 139 inches high. The outside walls taper, while the inside 

 walls are vertical, and there is a clearance of 60 inches between these 

 piers. A firing line, with a coupling box, is attached to the left- 

 hand pier, and by its aid the firing may be done from a safe distance. 



The extent to which the pendulum mortar is deflected is measured 

 by a detachable device consisting of a graduated scale, with its 

 vernier, which is set on a steel base fastened to a concrete footing 

 below and to the rear of the mortar, the movable parts being actuated 

 by a contact rod, set in guides, which bears at one end against a stud 

 bolt in the bottom of the mortar directly below the point at which its 

 center of gravity is located, and, at the other, on the scale. The 

 radius of the swing of the pendulum mortar, measured from the 

 knife-edge bearings to the center of the contact rod, or to the base of 

 the stud bolt, is 114/^ inches. The radius of the swing, measured 

 from the knife-edge bearings to the center of the trunnions of the 

 mortar, is 89f inches. The recording device measures the deflection of 

 the pendulum to within the one-hundredth part of an inch. 



The standard used for this test is 227 grams (one-half pound) of 

 40 per cent straight dynamite, stemmed with 1 pound of dry clay, 

 tamped with tamping sticks of standard pattern under a uniform 

 rate of pressure, and fired with a No. 6 electric detonator. The unit- 

 disruptive charge of another explosive is that weight of this explosive 

 that will, when fired under the prescribed conditions, give the same 

 deflection of the pendulum mortar as the standard dynamite charge 

 does. 



In making the test after the recording device is set, the '' cannon " 

 is loaded in the prescribed mamier and rolled up to within one- 

 sixteenth of an inch of the muzzle of the pendulum mortar, and stops 

 are so placed that this distance is maintained when the flanges of the 

 wheels of the truck are against them. The legs of the detonator are 

 then connected to the firing line, and the party loading, who has also 

 been carrying the safety plug with him, retires to the firing machine, 

 inserts the safety plug, and fires. 



