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18.

An interesting phenomenon connected with firing the chamber in air is the loudness of the sound produced by a comparatively small amount of powder.  This is, however, to be expected, inasmuch as the energy is entirely spent in producing motion of the air, whereas in the ordinary rifle, a large fraction of the energy of the powder becomes kinetic energy of the bullet.

[[underlined]] EXPERIMENTS WITH LARGE CHAMBER. [[/underlined]]

Inasmuch as all the steel chambers employed in the preceding experiments were of the same internal diameter (1.26 cm.), it was considered desirable that at least a few experiments should be performed with a larger chamber; first, in order to be certain that a large chamber is operative; and secondly, to see if such a chamber is not even more efficient than a small chamber.  This latter is to be expected for the reason that heat and frictional losses should increase as the [[underlined]] square [[/underlined]] of the linear dimensions of the chamber; and hence increase in a less proportion that the mass of powder that can be used with safety, which will vary as the [[underlined]] cube [[/underlined]] of the linear dimensions.  Evidence in support of this expectation has already been given.  Thus, for ordinary rockets, the larger rocket has the higher efficiency, as evident from Table I.

The large chamber was of nickel-alloy steel (Samson #3[[underlined]] A [[/underlined]]), of 115,000 lbs. tensil strength; for which the writer takes opportunity of thanking the Carpenter Steel Company.  This chamber had inside diameter, and diameter of throat,both twice as large as those of the chambers previously used; but the thickness of wall of the chamber and the taper of the nozzle were, however, the same.  The inside of the nozzle was well polished.  Fig. 12 shows a section of the chamber;