988 PROCEEDINGS OF SECTION H. 
No. 5.—NOTES ON THE ACTION OF CERTAIN 
EXPLOSIVES. 
By F. Marcuant, M.I.C.E. (Timaru, New Zealand). 
(Read Monday, 10 January, 1898.) 
| Abstract. | 
In the use of explosives in subaqueous work, the following notes 
on the burning of blasting gelatine and the sympathetic explosion 
of dynamite may be of interest to engineers :— 
1. For the purpose of loosening a harbour bottom before 
sinking some large mooring screws, a 3-inch pipe was 
lowered as a drill quide from a staging that had been 
erected, and was sunk through a3 3-foot loose gravel upper 
stratum to a hard sand surface, into which a 2h-inch 
hole was bored to a depth of 20 feet. 
When it came to loading the blasting charge holders, which 
were two galvanized-iron tubes, each 7 feet long and 2 inches in 
diameter, there was not sufficient dynamite, and the deficiency 
was made up with blasting gelatine, the proportions being about 
five-eighths dynamite and three-eighths gelatine. 
Although there was full knowledge of the high initial detona- 
tion required to explode the gelatine, it was naturally thought 
that when the dynamite exploded the gelatine intermixed with it 
would also explode. 
The result, on firing by an electric battery from the staging the 
charges in the tubes, which filled 14 feet of the bore- hole, was an 
uprush from the guide- pipe of a roaring blast of violet- coloured 
smoke shooting up 20 feet into the still air and forming a mush- 
room shaped cloud which quickly fell on the staging, which the 
men had already, without mishap, quitted by a boat. 
In previously sinking six screw moorings in the same harbour 
with precisely similar operations, but with dynamite alone as the 
explosive, no such smoke occurred. 
The conclusion therefore deduced is, that the dynamite in 
exploding does not give a sufficiently quick series of vibrations to 
effect the detonation of the gelatine, and that the latter simply 
burnt furiously without having any explosive effect. 
On the Sympathetic Explosion of Dynamite. 
In breaking up portions of a wreck in about 21 feet of water, 
charges of dynamite, each about 7 lb., in galvanized-iron canisters, 
were attached by a diver, and a line attached, its upper end being 
fastened to a float. 
