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15.

contact of the latter with the nozzle. The wire [[underlined]] W [[/underlined]] was so held that, although it exerted a pull on the wire [[underlined]] w [[/underlined]], it nevertheless offered no resistance in the direction of motion of the ejected gases.

Two dense smokeless powders were used; Du Pont pistol powder #3, a very rapid dense nitrocellulose powder, and "Infallible" shot-gun powder, of the Hercules Powder Company. The heat values in all cases were found by bomb calorimeter. [[superscript]] (2) [[/superscript]]  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 #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, Fig. 10, containing weights, and supporting 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 made certain that the plank actually was horizontal 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 swinging. Current for firing the charge was lead through two drops of

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(2) It was found necessary to use a sample exceeding a certain mass, as otherwise the heat value depended upon the mass of the sample.