14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. "J V 



part of the wadding, in contact with the powder. To the other end 

 of this platinum wire, a short length of the copper wire passed to the 

 side of the wadding, and made electrical contact with the wall of the 

 chamber. A fine steel wire, W, 0.24 mm. in diameter, served to pull 

 the copper wire, w, tightly enough to prevent contact of the latter 

 with the nozzle. The wire, W, was so held that, although it exerted 

 a pull on the wire w, it nevertheless offered no resistance in the direc- 

 tion of motion of the ejected gases. 



Two dense smokeless powders were used : Du Pont pistol powder 

 No. 3, a very rapid dense nitrocellulose powder, and " Infallible " 

 shotgun powder, of the Hercules Powder Company. The heat values 

 in all cases were found by bomb calorimeter.^ All determinations 

 were made in an atmosphere of carbon dioxide, in order to avoid 

 any heat due to the oxygen of the air. The average heat values were 

 the following: 



Powder, in ordinary rocket 545-0 calories/gm. 



Powder, in Coston ship rocket 528.3 



Du Pont Pistol No. 3 972.5 



" Infallible " 1238.5 



The ballistic pendulum used in determining the average velocity of 

 ejection, for the small chambers, consisted essentially of a plank, B, 

 plate 3, figure i, carrying weights, and suppo'rting the chamber, 

 or gun, C, in a horizontal position. This plank was supported by fine 

 steel wires in such a manner that it remained horizontal during 

 motion. In order to make certain that the plank actually was hori- 

 zontal in all positions, a test was frequently made by mounting a 

 small vertical mirror on the plank, with its plane perpendicular to the 

 axis of the gun, and observing the image of a horizontal object — as 

 a lead pencil — held several feet away while the pendulum was swing- 

 ing. Current for firing the charge was lead through two drops of 

 mercury to wires on the plank. A record of the displacements was 

 made by a stilus consisting of a steel rod, S, pointed and hardened at 

 the lower end. This rod slid freely in a vertical brass sleeve, attached 

 to the under side of the plank, and made a mark upon a smoked glass 

 strip, G. In this way the first backward and forward displacements 

 of the pendulum were recorded, and the elimination of friction was 

 thereby made possible. 



The data and results of these experiments are given in table II, 

 in which d is the displacement corrected for friction. 



* It was found necessary to use a sample exceeding a certain mass, as other- 

 wise the heat value depended upon the mass of the sample. 



