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POPULAR SCIENCE REVIEW. 
with certainty on its doing its work. Moreover, it must be 
capable of being stored for a long time without injury or 
deterioration ; and it must be safe to work with, so as to avoid 
as far as possible the chance of an accidental explosion. This 
last condition at once excludes picrate of potassium, picric 
powder, and all similar compounds, which, though they are 
very powerful, are also terribly dangerous. Grunpowder fulfils 
all the required conditions, and it was used almost invariably 
by the Confederates. Their experiments seem to point to fine- 
grained powder as better than any other variety ; but a much 
longer series of trials would be necessary before finally deciding 
on this matter. But if we could obtain an explosive equally 
safe and more powerful, weight for weight, it is clear that it 
would be far better suited for our purpose, being more port- 
able, requiring smaller cases, and giving greater buoyancy to 
the submerged torpedoes. This we find in gun-cotton — a pre- 
paration of waste cotton which is impregnated with nitric and 
sulphuric acids. Its explosive force may be taken as at least 
four times that of gunpowder ; it can be stored without dete- 
riorating, and with almost perfect safety. Even if it is acci- 
dentally set on fire in air, it burns with a bright flame without 
exploding, and besides the advantages we have enumerated, it 
possesses another which at once marks it as the best for forming 
the charges of torpedoes. Grun-cotton, when fired with a 
detonating fuze,* developes its full force instantaneously, and 
there is therefore no need of using the strong case necessary to 
ensure the complete explosion of gunpowder. When gun-cotton 
is used in torpedoes, all that is necessary in the case is, that it 
should be water-tight, and there is no need of its possessing 
the great strength which would be otherwise required. A 
detail of a few experiments will show how efficiently it can be 
used under water, even in the lightest of cases. In 1870 it 
was very successfully employed at the Isle of Sombrero, in 
blasting rocks at a depth of 20 or 25 feet under water. The 
charges were from 8 to 10 lbs. of compressed gun-cotton, 
and the cases were made of tarred paper. These charges, 
which may be looked upon as miniature torpedoes, were placed 
in the fissures of the rock ; and after the explosion the debris 
they brought down was dredged up. In June 1868 both gun- 
powder and gun-cotton were used in destroying a sunken 
iron steamer in the Thames, and this demolition affords very 
striking evidence in favour of gun-cotton. “ Amidships, 
where the engines and boiler and machinery were situated, a 
charge of 300 lbs. of gunpowder was fired in contact with the 
side of the wreck, but it made no breach whatever, owing to 
* That is, with a fuze primed with detonating fulminate of mercury. 
