296 
othe 
might regard the thin layer of compressed water as a casing; certainly its velocity and energy is 
comparable with that of a steel case surrounding a similar charge, At x = 1,088 charge radli, the 
water is compressed from its original thickness .088 to .056 and its average velocity Is about 
1450 m.Jsecond, 
The additional wastaye between x = 6,08 and x = 55 is only 66 cal./gm. Thus we have that 
the energy wastage at the limit of damaging range Is 30% of the chemical energy, and is therefore 
roughly equal to that of the energy of the pulse at the same range. 
It will be noticed that the total energy of the T.W.T. Is taken as 600 cal.fgm ‘This is 
perhaps on the low side. Jones, in R.C.212, estimates the chemical eneryy released per gm, of 
T.N.T. at loading density 1,5 gm./c.c. to be 1090 cal./ym, However, the adiabatic used by Taylor, 
R.C.178, was only approximate, and the total energy per gam., assuming Taylor's pressure and mass 
velocity curves together with Jones’ adlabatics, R.C.212, works out at 800 cal./gm. A recalculation 
of the spherical detonation waves in TN.T. for loading densities 1.5 and 1.0 Is In progress, and a 
report on the results will be made shortly. 
The energy of the disturbance at the end of the step-by-step calculations Is 700 cal./gm. 
Most of the errors certainly occur in the Inner reglonse 
Radius of bubble and velocity of interface. 
Table 5 gives the radius of the bubble in cm. at times t microseconds, for a charge 
initially 50 cm, radius. The radial velocity tn metres per second Is also given. 
TABLE 5. 
Pass fre fee fe a 
efter Sriac eesti 
The overtaking effect and time of rise. 
As mentioned earlier, the records of underwater explosions aopear to show a finite time of 
rise T to the peak pressure. If this effect Is reat (apparently there Is stil) some doubt about it), 
the origin of T might be sought in any of the followings— 
(1) the effect of the case, 
(2) detonation not spherical, so that the gauge records a series of elementary 
oulses bullding up to a maximum, 
(3) change of phase of water. 
The following table indicates that (1) and (2) taken separately are unlikely to provide the 
full explanation of T. We have calculated a distance D In terms of the shock wsve radius R cm. for 
a charge of Initial radius 50 cm, At the instant that the spherical detonation wave reaches the 
surface of the charge an expanding sound pulse in the water has Its leading edge at 50+ D; OD is 
then chosen so that the shock wave overtakes the sound pulse at radius R. 
TABLE 6. 
——— 
Thus, If the sound wave had a start of 500 microseconds over the shock wave, the sound pulse 
would just be masked by the shock wave at distance 304 cm. Adjusting the scale to a 300 1b. charge 
gives the start as 2% microseconds, To give an observed T of » Say, 50 microseconds requires that 
the sound wave must be given a start 320 microseconds. This seems too large to be attributed to 
the effect of the case or non=spherical detonation, 
Discussion .... 
