EXPLOSIVES FOR GEOPHYSICAL PROSPECTING 29 
the same manner as sausages are filled. This method of packing has 
its limitations so far as producing a firm cartridge is concerned, in 
that, for efficient operation, the gelatin must be relatively soft and 
plastic. While the standard explosive proved well adapted to the old 
refraction method, it was not satisfactory for reflection shooting be- 
cause the cartridges lacked the necessary stiffness and rigidity to with- 
stand the rough treatment used in forcing them down ragged or ob- 
structed holes. To overcome this deficiency, the gelatin was manu- 
factured on the stiffest formula compatible with the extrusion process 
and was packed into specially designed heavy paper shells which 
offered more resistance against bulging or buckling under pressure. 
Even with this special packed explosive, some trouble was experi- 
enced, particularly during the hot summer months, due to the inher- 
ent softness of a gelatin dynamite. Trouble in loading difficult holes 
was minimized to some extent by placing the cartridges in tin torpe- 
does before lowering the charge into the shot holes. While this method 
was of some benefit, it did not prove to be the complete answer to the 
loading problem, since, occasionally, the pressure exerted on the 
tamping pole was sufficient to expand the explosive cartridge, causing 
the tin torpedo to burst and become lodged at some point midway 
down the hole. In addition, the cost of these torpedoes increased the 
explosive expense of seismograph crews. 
More recently, another specially designed 60 per cent explosive 
has been developed for that seismograph trade desiring a powder even 
harder and firmer than the stiff, heavily wrapped 60 per cent am- 
monia gelatin referred to before. This explosive differs from the pre- 
ceding type in that it is hand packed. As a general rule, this type has 
proved very satisfactory under severe loading and hot weather con- 
ditions. 
One other type of gelatin has been developed recently for certain 
shooting conditions encountered in seismograph prospecting. In the 
Kansas area, it has been found that very small charges, ranging 
from an electric blasting cap alone to one-half pound of powder, will 
set up seismic vibrations of the required magnitude for efficient 
recording. The method of loading usually employed in that district 
is to mold a small piece, say one-sixteenth of one pound, of gelatin 
around the detonator and wrap the combination in a piece of paper, 
which in turn is held in place by means of tape or a rubber band. 
Obviously, neither of the types of gelatin previously discussed would 
prove altogether satisfactory for molding purposes. For this reason, 
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