i8 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 7I 



3^ foot length of 2-inch pipe, P, by set-screws. Within this pipe, 

 above the chamber, was fastened a length of 2-inch steel shafting, to 

 increase the mass of the movable system. This system was supported 

 by a half-inch steel pin, E. 



On firing, the recoil lifted the above system vertically upward 

 against gravity, the extent o'f this lift, or displacement, being re- 

 corded by a thin lead pencil, slidable in a brass sleeve set in the pipe 

 at right angles to the pin E. The point of the pencil was pressed 

 against a vertical cardboard, C, by the action of a small spring. This 

 method of measuring the impulse of the expelled gases will be called 

 the " direct-lift " method ; and the theory is given in Appendix A, 

 page 60. 



P W 



Fig. 3, 



Although rebound of the gases from the ground would probably 

 have been negligible, such rebound was eliminated by a short plank, 

 D, covered with a piece of heavy sheet iron, and supported at an angle 

 of 45° with the horizontal. This served to deflect the gases to 

 one side. 



The results of two experiments, 51 and 52, with this large chamber, 

 are given in table II. In experiment 51, with Du Pont powder, the 

 powder was packed rather loosely. Any increase in internal diameter 

 was inappreciable, certainly under o.oi mm. In experiment 52, 

 the Infallible powder was somewhat compressed. After firing, the 

 chamber was found to be slightly bulged for a short distance around 

 the middle of the powder chamber, the inside diameter being in- 

 creased from 2.6 cm. to 2.7 cm., and the outside diameter from 

 5.08 cm. to 5.14 cm. The efficiency (64.53 P^^ cent) in experiment 

 51, and the velocity (7,987 ft./sec.) in experiment 52 were, respec- 

 tively, the highest obtained in any of the experiments. 



The conclusions to be drawn from these two experiments are: 

 First, that large chambers can be operated, under proper conditions, 



