OCEAN BOTTOM— PIGGOT 211 



Inside the muzzle end of the powder chamber is an annular 

 shoulder, one-eighth inch from the muzzle. On this shoulder rests 

 a steel disk, one-eighth inch thick, with its outer surface flush with 

 the end of the powder chamber. Its function is to take the strain 

 of the hydrostatic pressure and thereby prevent distortion or break- 

 ing of the rupture disk. Between the pressure disk and the rupture 

 disk is a thin copper disk, which serves as a gasket. The rupture 

 disk is of steel and of such thickness and strength that it will allow 

 the pressure within the cartridge to build up to the proper working 

 pressure before it ruptures and releases the energy to the mechanism. 



POWDER CHARGE 



The explosive charge furnishes the energy required to do the 

 necessary work. This varies with the depth and the character of 

 the bottom. The charge consists of a primer, 1 gram of high-speed 

 black powder, 1 gram of rifle powder, and a varying number of 

 pellets of 155-mm howitzer powder. The 2 grams of small powder 

 play the double role of promoting ignition and quickly building up 

 a pressure, in which environment the large-grained powder functions 

 explosively. If this high pressure were not provided, the latter 

 would not burn properly. 



The total available energy is regulated by counting into the car- 

 tridge a varying number of pellets of the big powder. This required 

 energy is of three parts: (1) That which is necessary to overcome 

 the hydrostatic pressure at a particular depth; (2) that which is 

 necessary to overcome the inertia of the bit and to put it into 

 motion; and (3) that required to drive the bit into the particular 

 material encountered. Only the second can be determined in ad- 

 vance; the other two must be provided for at each sounding. The 

 possible work that can be done is a combination of the total available 

 energy and an intensity factor — i. e., the pressure at which the ex- 

 plosive gases are released. The control of this "working pressure" is 

 accomplished by the steel rupture disk at the mouth of the cartridge. 

 Up to the time this disk is blown out, the powder is protected from the 

 water. These disks are relatively thin, and, therefore, capable of dis- 

 tortion, and at a certain depth the hydrostatic pressure might con- 

 ceivably be greater than the desired "working pressure" — hence, the 

 steel "hydrostatic pressure disk", which relieves the rupture disk of 

 all strain and enables it to be adjusted to the requirements. 



FIRING MECHANISM 



The firing mechanism is simple and rugged and can be easily re- 

 moved for cleaning or replacement. It consists of a trigger, which is 



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