METHODS OF TESTT5TG EXPLOSIVES MUNROE. 301 



detonator, of the grade recommended by the manufacturer of the 

 explosive, being inserted in tlie lower end of the lower cartridge, 

 secured in place, and fired. By proceeding tentatively the distance 

 at which detonation by influence ceases is said to be established 

 within very narrow limits. For comparison between different ex- 

 plosives cartridges of uniform size are used, such as 1^ inches in 

 diameter by 8 inches in length. This may necessitate the repacking 

 of the explosive, and when this is done care should be taken to pre- 

 serve the original density, since this is a factor in this behavior of 

 explosives. 



While the explosive should be sufficiently susceptible to detona- 

 tion to be fired with certainty it should not be so sensitive to per- 

 cussion as to be dangerous in handling, transportation, or use. This 

 sensitiveness of explosives to the effect of direct blows is determined 

 by the impact machine shown in plate 9, which consists of a vertical 

 steel framework carrying two giiide rods between which a j'oke, to 

 which the impact weight or hammer is attached, is guided; an anvil 

 upon which the charge of explosive is placed; and a soft-steel 

 plunger which rests upon the anvil and upon which the hammer 

 impinges in its fall. The yoke is provided with jaws which engage 

 the lugs of an endless chain moving behind it, and by this mechanism 

 the yoke with its attached weight is raised to any desired height. 

 By means of an electric current the yoke may be magnetized and 

 demagnetized at will so that when magnetized it will attract and 

 support the hammer to such an extent that both may be raised 

 together by the endless chain to any predetermined height, at which 

 point the yoke is demagnetized, the hammer or weight is released 

 and the latter then falls through the intervening distance and im- 

 pinges upon the plunger. The stop which arrests the upward travel 

 of the magnetized yoke and automatically causes its demagnetiza- 

 tion is operated by a vertically driven precision screw on the right- 

 hand side of the frame, which is also geared to a recording device 

 which measures the height from which the hammer falls. By the 

 aid of this screw and its accessories one is able to set the stop in 

 advance so as to secure anj'- desired distance of fall for the hammer 

 within the capacity of the machine. 



The hard-steel anvil is set firmly on a liea\y iron base and it is 

 surrounded by a tubulated jacket through which water may be cir- 

 culated, so as to bring the temperature of the anvil and of the charge 

 of explosive placed upon it to any desired temperature and to keep 

 it there. The plunger is held lightly in place by a steel guide which 

 forms a part of the base support for the vertical-guide rods. It is 

 essential that the faces of the plunger and of the anvil which are in 

 contact should be absolutely true and plane. As the impacts and ex- 

 plosions produce deformation of the metal, the plunger is made of 



