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12.

P[[underlined]] ART II [[/underlined]].  [[underlined]] EXPERIMENTS [[/underlined]].

[[underlined]] EFFICIENCY OF ORDINARY ROCKET [[/underlined]].

The average velocity of ejection of the gases expelled from two sizes of ordinary rocket were determined by a ballistic pendulum.  The smaller rockets, [[underlined]] C [[/underlined]], Fig. 2, averaged 120 grams, with a powder charge of 23 grams; and the larger, [[underlined]] S [[/underlined]], the well known Coston ship rocket, weighed 640 grams, with a powder charge of 130 grams.  Fig. 3. shows the rockets as compared with a yard-stick, [[underlined]] Y [[/underlined]].

The ballistic pendulum, Figs. 4 and 5, was a massive compound pendulum weighing 70.64 Kg (155 lbs.) with a half period of 4.4 seconds; large compared with the duration of discharge of the rockets.  The efficiencies were obtained from the average velocity of ejection of the gases, found by the usual ballistic pendulum method, together with the heat value of the powder of the rockets, obtained by a bomb calorimeter for the writer by a Worcester chemist.

The results of these experiments are given in the following table: