981 
Argon-surrounded flash charges were adapted at UVERL 7 for use underwater and 
proved satisfactory. By using conical rather than spherical charges it was 
possible to produce a given amount of useful light with less explosive. The 
amount of light emitted by the charges was about halved if the gas layer was air 
instead of argon. Tests were conducted with charges coated with mercurous chloride 
and sodium chloride (because of their emission spectra), but the results were 
erratic. The various types of flash charge prepared at UERL are illustrated in 
Figure 5. 
(i) Glass enclosed flash charges for depths down to 20 feet. Since this type of 
flash charge was used most, its fabrication will be discussed in some detail. 
A primacord fuze is cut to the desired length and one end rolled tightly in a 
2x 2x 1/32 in. sheet of lead with 1/8 in. of primacord projecting beyond 
the lead (see 1C of Figure 5). The function of the lead is to prevent deto- 
nation except that starting from the center of the sphere. To obtain maximm 
charge density and to minimuze segregation, all of the air should be driven 
out of the molten pentolite and the mix should be as cool as possible when 
poured. The charge is cast in a well-greased (e.g. petroleum jelly) plaster 
of paris mold (Figure 6) with the exposed end of primacord fuze in the center. 
The half molds are set over one another on their rims with the fuze in the 
groove provided and with the filling hole on top. Molten explosive is poured 
in up to the base of the filling hole and as the mix cools and shrinks, more 
is added to keep the level constant. When solid, the charge is easily removed 
by taking apart the molds. Molds may be cooled, regreased, and used again 
many times, : 
Charges may also be case as two hemispheres. One hemisphere is cast with the 
primacord fuze in place and is removed from the mold when the explosive 
solidifies. Molten explosive is poured into the second mold up to ay level 
of the fuze groove and the first half (with fuze) is placed on top. The 
completed charge is easily removed from the mold when the second half 
solidifies. 
The charge is next mounted in the round bottom glass flask which has been 
split into two halves (see 1B, 1C of Figure 5) by the hot wire technique 
familiar to glassblowers. Rubber tape is wrapped around the lead covered 
primacord fuze to provide a snug fit in the neck of the flask and to center 
the charge. There is a 3/16 in. space between the charge and the wall of the 
flask. A small chip of glass is removed from one of the split edges of the 
flask to provide a filling hole for the gas. The split halves of the flask 
are glued together with transparent tygon paint or Duco cement and the region 
over the seam is painted twice with the cement for waterproofing. Plaster 
of paris is poured into the neck of the flask to fix the charge in position, 
aid in waterproofing and minimize the leakage of gas. Bostik cement (a 
heavy-bodied rubber compound) or vaseline is placed over the plaster of paris 
to waterproof completely the mouth of the flask. Just before shooting, the 
charge is placed in a steel (for safety) vacuum desiccator, the air evacuated 
through the filling hole and argon allowed to flow in an atmospheric pressure. 
The filling hole is then resealed with a piece of scotch tape and Bostik. 
(44) Conical flash charges for depths down to 10 feet. Only a part of the light 
distributed by the shperical type flash charge described above is used in 
illuminating the field of view of the camera. The lighting efficiency may 
be improved by using a reflector behind the flash charge. However, there 
was little loss in light when the spherical charge was replaced by a conical 
of Charges for Sti of Explosion Phenomena at » by P. Newmark and 
BE. L. Paterson, NDRC Report A-381 (OSRD 6259); also The Preparation and Testing of High- 
“Sea Short Duration Underwater Flares, by E. L. Patterson, NDRC Report A-382 
OSRD e 
While this technique leads to some cavitation at the center of the cold charge, it was 
found in practice to make little or no difference for this purpose if the precautions 
noted above were taken. 
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