Chevalier d'Arcy, 1760. also experimented on the pressure of powder and the velocity of the bullet in a musket barrel; this he accomplished by shortening the barrel successively, and measuring the velocity obtained by the ballistic pendulum; thus reversing Noble's procedure of gradually lengthening the gun.

But the most modern results employed with gunpowder are based on the experiments of Noble and Abel (Phil. Trans., 1875-1880-1892-1894 and following years).

A charge of powder, or other explosive, of varying weight P lb, is fired in an explosion-chamber (fig. 7, scale about 1/5) of which the volume C, cub. in., is known accurately, and the pressure p, tons per sq. in., was recorded by a crusher-gauge (fig. 6).

The result is plotted in figs. 8 and 9, in a curve showing the relation between p and D the gravimetric density, which is the specific gravity of the P lb of powder when filling the volume C, cub. in., in a state of gas; or between p and v, the reciprocal of D, which may be called the gravimetric volume (G.V.), being the ratio of the volume of the gas to the volume of an equal weight of water.

The results are also embodied in the following Table;—

Table 1.

G.D.

G.V.

Pressure in Tons per sq. in.

Pebble Powder.

Cordite.

0.05

20.00

0.855

3.00

6

16.66

1.00

3.80

8

12.50

1.36

5.40

0.10

10.00

1.76

7.10

12

8.33

2.06

8.70

14

7.14

2.53

10.50

15

6.66

2.73

11.36

16

6.25

2.96

12.30

18

5.55

3.33

14.20

20

5.00

3.77

16.00

22

4.54

4.26

17.90

24

4.17

4.66

19.80

25

4.00

4.88

20.63

26

3.84

5.10

21.75

30

3.33

6.07

26.00

35

2.85

7.35

31.00

40

2.50

8.73

36.53

45

2.22

10.23

42.20

50

2.00

11.25

48.66

55

1.81

13.62

55.86

60

1.66

15.55

63.33