302 ANNUAL REPOKT SMITHSONIAN INSTTTtTTlON, 1910. 



soft steel, so that the deformation may accumulate on it, and there- 

 fore it is very frequently turned up on a lathe and reground to true 

 up its face. 



The hammer used weighs 2,000 grams. The soft-steel plunger 

 weighs 900 grams, and the maximum height from which the ham- 

 mer can be dropped is 100 centimeters. The weight of charge of 

 explosive used is 0.02 gi'am. The temperature of the anvil and the 

 explosive at the time of testing is 25° C. 



In making the test the explosive is weighed out on a chemical 

 balance and the charge so wrapped in tin foil as to make a pellet 

 in the form of a flat disk 1 centimeter in diameter. The hammer is 

 raised, the stamp is lifted, the pellet is placed on the anvil, the stamp 

 is pressed gently down upon it, so as to insure a good contact, and the 

 whole is left to attain the standard temperature. The stop is then 

 set by judgment and the hammer raised until it is disengaged at the 

 chosen height and falls upon the plunger. If no explosion ensues, 

 the stop is set at a greater height and the hammer released, and this 

 method of procedure is repeated until either explosion occurs on im- 

 pact or the maximum range of the machine is reached. When ex- 

 plosion does occur the test is repeated with a fresh charge of ex- 

 plosive and slightW diminished distance of fall, and one thus 

 proceeds tentatively until such a height of fall for the hammer is 

 reached that there is no explosion, and yet if that height be exceeded 

 by but 1 centimeter an exi)losion occurs. This point is then fixed 

 by four additional tests, giving the. same results. 



Provided all other conditions remain the same the brisant or 

 shattering effect of an explosive varies with the velocity with which 

 the chemical reaction, or explosion wave travels through the column 

 or charge of the explosive. Where explosives are fired by detonation 

 this movement, as measured in definite terms of time and length, is 

 styled the rate of detonation of the explosive. The making of such 

 determinations is not new, for Abel measured the rate of detonation 

 in guncotton, nitroglycerine, and dynamite nearly 40 years ago,^ and 

 Berthelot did so some 10 years later.^ What has been done in recent 

 years has been rather in the standardizing of the method, the im- 

 provement in the details and operation of the chronograph, and the 

 introduction of the method into general practice. 



To assure a definite and uniform area of exposiire, the cartridges 

 of explosives in their original wrappers, but with the ends cut off so 

 as to avoid the damping effect of the layers of paper, are packed 

 in tubes of thin sheet iron 42 inches in length and varying in 

 diameter from 1^ to 2 inches, according to the character of the ex- 

 plosive to be tested. When the tube has been charged two copper 



iphil. Trans. 164, 377; 1874. 2 j^nn. chim. phys. (6) 6, 556. 



