iSjg.j Measurement of Powder Pressures in Cannon. 363 
gun. The receiver was immersed in a water-bath kept at 
the proper temperature. The pressures, temperatures, and 
lengths of stroke are given below ; — - 
Compression of Oil in Steel Piezometer. 
Pressure. Length of stroke at — 
Per square inch. 
6o° 
50 ° 
Lbs. 
In. 
In. 
10,000 
0*2148 
0*2 4-01 
15,000 
0*2780 
0*3266 
20,000 
0*3656 
0*4108 
25,000 
— 
0*5670 
We now arrive at the experiments in which the piezometer 
was used to record the compressions produced by the pres- 
sure of fired gunpowder under various conditions, and from 
which the pressures were to be derived. They were made 
at Washington Arsenal, D.C., commanded by Major Alfred 
Mordecai, who heartily co-operated in their conduct. 
Two six-pounder guns, one of iron the, other of bronze, 
were used in these experiments. The diameter of the bore 
of each, at the seat of the shot, was 3*69 ins., very nearly. 
The iron gun was used in the first three experiments, in 
which the piezometer was attached to the bottom of the 
bore. It was afterwards pierced through its side to receive 
the piezometer inclosed, as described in the Report, in a hol- 
low steel plug, the centre of the opening being 1 *5 ins. forward 
of the bottom of the bore. It was used in this form in 
several experiments. The bronze gun was, however, used 
in the greater number. It was pierced with nine holes at 
different distances from the bottom, beginning at 1 inch 
and ending with 47*8. They were arranged alternately to 
the right and left of the central vertical plane, in the upper 
half of the gun, and inclined 45 0 to that plane. 
A solid plug was fitted to each hole, and was withdrawn 
only to permit the insertion of the piezometer. 
Small holes to receive a thermometer with an elongated 
bulb were drilled near the openings, mentioned above, 
extending to within a short distance from the bore. 
Several experiments were made to ascertain pressures in 
a musket barrel. A portion of the bore at the breech-end 
was enlarged enough to receive the piezometer, and was 
separated from the forward portion by a ring screwed to 
place and a leather disc closing its opening, as described in 
connection with the hollow plug. The piezometer was 
introduced from the rear, the surrounding space filled with 
