JuLy 16, 1914] 
ceeds much more quickly than when the grains are 
large, and the powder maker takes advantage of this 
fact in preparing powder for rifles and the various 
sized large guns. 
Detonation, on the other hand, has to be started by 
a sufficiently strong impulse, such as the explosion of 
a charge of mercury fulminate ; it proceeds much more 
rapidly and is due to the formation of an explosion 
NATURE 
519 
oxidation, the products are carbon dioxide, carbon 
monoxide, hydrogen, water, and nitrogen, but the 
relative proportions vary with the pressure developed. 
When such an explosive is fired in a closed vessel 
under different densities of charge, that is, different 
quantities of explosive in the same volume, the volume 
and composition of the gas varies with the pressure 
developed by the explosion. The carbon dioxide and 
Fic, 1.—Blast at Lord Penrhyn’s slate quarries. 
wave that has. a velocity of thousands of metres a 
second. 
Black gunpowder and allied explosives, as well as 
the smokeless powders, belong to the first or combus- 
tion class, and they are commonly designated ‘‘low”’ 
explosives. 
‘“ High ”’ explosives indicate those, such as dynamites 
and nitrate of ammonia explosives, which detonate 
Fic. 2.—Berthelot calori-metric bomb. 
and have a greater shattering action than the former. 
The volume and composition of the gas produced, 
both in regard to the power of the explosive, and, in 
the case of mining explosives, the health of the miner, 
are of great importance. These gases are largely 
determined by the original composition of the explo- 
sive. 
When there is insufficient oxygen for 
NOl 2333, VOL. 93| 
complete 
hydrogen increase and the carbon monoxide and water 
diminish as the pressure increases; also, at high pres- 
sures, considerable amounts of methane are formed. 
In the foregoing, it has been assumed that complete 
explosive decomposition has taken place. 
When a high explosive burns, instead of explodes, 
the chemical changes are not only very much slower 
and the disruptive effect practically nil, but the char- 
nner 
iH 
ABBE 
b 
a 
: 
& 
Be 
2 
Fic. 3.—Ballistic pendulum, Home Office testirg 
station. 
acter of the gases is entirely changed, large volumes 
of poisonous nitrous fumes along with other gases 
being produced. 
The temperature developed by an explosive is of 
importance, because the higher the temperature the 
greater the erosion of the guns. 
Nearly all blasting explosives, except black powder, 
are fired by means of a detonator. Fulminate of 
