286 



Professor Bertram Hopkinson 



[Jan. 26, 



rod, distant three-qnarters of an inch from it. With the gun-cotton 

 hard up against the steel the pressures are probably about twice as 

 great, and the curve similar in form. It is, of course, impossible to 

 do this experiment within the walls of this lecture room, the explo- 

 sion, while not very violent, is sufficiently so to necessitate its being 

 carried out in the open. But I can readily show you a very similar 

 experiment, in which the pressure is produced, not by the detonation 

 of gun-cotton, but by the impact of a small rifle bullet. [Experiment 

 shown.] 



O 2 4- 6 8 



/ Ounce of GuncoUon •% from end of /:? bar. 

 Observed- ^ifiLs Ihus : o 



1 Z 3 



TzfTte , irv Hurtdredi Thoibsandths of a- SecotzcL 



Fig. 7. - ^ 



I have on the table some specimens to show the [] effects 3 of deto- 

 nating larger quantities of gun-cotton. Here is a steel plate which 

 has been broken by firing a charge of about 1 lb. in contact with 

 it. It is interesting to note the character the fracture produced. 

 This plate is a good quality of mild steel, such as is used for making 

 boilers. It would be possible by a steadily applied pressure to bend 

 it double without fracture, yet as the effect of the blow delivered by 

 the gun-cotton it is broken with very little bending, almost as though 

 it were cast iron or very hard steel. Time will not permit of my 

 going further into the interesting question, of course a very import- 

 ant one in connection with our subject, of the effect on the character 



