30 G. H. LOVING AND G. H. SMITH 
another 60 per cent ammonia gelatin characterized by its sticky, rub- 
bery, plastic nature has been developed for this particular type of 
loading. 
The several gelatins just discussed fulfill the qualifications nor- 
mally required by the reflection method of geophysical prospecting. 
Occasionally, however, shots are made in very deep water-filled holes, 
say 200 feet or more in depth. Under such high water pressures, the 
powders under discussion may not always detonate completely, the 
visual evidence of this condition being the evolution of brown vapors 
from the mouth of the hole. In this connection, probably the most 
satisfactory explosive for shooting under unusual depths of water is 
60 per cent Hi-Velocity gelatin, a patented product not made by all 
manufacturers. This explosive was developed several years ago for 
submarine blasting and has rapidly become popular for especially 
severe shooting conditions. 
Needless to say, the four types of gelatin which have been de- 
scribed possess almost identical explosive properties in speed and 
strength. These explosives are packed in any size ranging from 
14 inches X8 inches or one-half pound, to 3 inchesX12 inches or 5 
pound cartridges, the most popular being the 1, 23, and 5 pounds 
cartridges, which are 2 inchesX6 inches, 2 inchesX16 inches, and 3 
inches X 12 inches, respectively, in size. Cartridging to a known weight 
at the explosives plant relieves shooting crews of this responsibility. 
ELECTRIC BLASTING CAPS FOR GEOPHYSICAL PROSPECTING 
In the usual types of work requiring electric blasting caps, the 
detonator serves only one purpose, that of initiating the explosive 
charge in which it is embedded. On this basis, the cap is not required 
to satisfy any precise limitations as to speed or uniformity of de- 
tonation. In seismograph explorations, however, these points are of 
prime importance and have prompted the development of an electric 
blasting cap of special design. Before discussing this work, it seems 
well to give a brief description of the construction of an electric blast- 
ing cap and its function in geophysical prospecting. 
The component parts of an electric blasting cap are; (1) a metal 
container or shell, (2) the pressed explosive charge or charges, (3) a 
firing circuit, surrounded by a material which ignites when current is 
applied to the cap and thus accomplishes initiation of the pressed 
charge, and (4) the waterproofing column and sulfur seal. The shell 
is of such simple construction that no further mention seems neces- 
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