424 
MINUTES OF PROCEEDINGS OF 
It will be noticed that even in the most favourable case for comparison, 
viz., that in which the cylinder was just burst, the pressure obtained by 
gunpowder was about double the hydrostatic pressure. This is a very serious 
discrepancy, and is sufficient to cast a doubt on the accuracy of his method 
of measuring the pressure, which was by fixing a “ pressure gauge 3 * in the 
gun at various distances along the bore. The pressure was inferred from 
the distance an indenting tool was pressed into a wrought-iron or copper 
specimen, the force necessary for any particular indentation having first 
been obtained by statical pressure. 
Tig. 4 shows this gauge. 
Bodman tried the effect of varying the charge and shot in a gun. He 
fired a 43 lb. round shot with charges varying from 3 to 12 lbs., and found 
that the pressure varied very accurately as the charge; he also fired from 
the same gun, with a fixed charge of 5 lbs., shot varying from 35 to 85 lbs., 
and again found that the pressure varied with the shot. He says :—* 
fC The nearest approximation to any regular law of variation of pressure due to 
variation of charge and projectile, discoverable in the results obtained from the 
series, with a constant weight of projectile and variable weight of charge, and that 
with a constant weight of charge and variable weight of projectile is, that with, a 
constant diameter the pressure increases directly as the product of the weight of 
the charge by that of the projectile.” 
This law is much severer than that of Bumford, and, unless we account for 
it by his method of measurement being inaccurate, we must do so by con¬ 
cluding that the rate of combustion increased with the charge and projectile 
on account of the greater heat and pressure developed. 
He next tried varying the bore, with the following results j— 
“ Table showing the velocity of shot in feet per second, and pressure of gas per 
square inch (in tons) due to equal columns of powder behind equal columns of 
metal, when fired in guns of different diameters of bore, each result being a mean 
of ten fires. 
o 
• 
a3 
hC 
O . 
43 cu 
. • 
Velocity, f.s. 
Pressure at different distances from bottom of bore. 
o § 
P 
i 
Weigh 
charg 
Weigh 
shot 
At 
bottom. 
-4-3 
<1 
CD 
03 
03 
-*3 
<5 
b 
to 
+3 
<1 
o 
00 
<1 
ins. 
7 
ins. 
•07 
lbs. 
6-13 
lbs. 
74-44 
904 
16-3 
7-1 
3-7 
2-9 
3-1 
3-6 
3-0 
9 
•09 
8:48 
124-42 
888 
30-0 
9-4 
7-9 
6-7 
13-1 
9-4 
10-2 
11 
•11 
12-67 
186-03 
927 
38-7 
13-1 
12-4 
10-0 
12-7 
15-1 
11-2 
“ The points most worthy of note in these results are the very marked increase 
in the pressure of gas as the diameter of bore increases, and that the indications of 
pressure are greater at 56, 70, and 84 ins. than at 42 ins., especially in the 9-inch 
and 11-inch guns.” 
* “ Experiments, &c.’ 
