ge
quantities of roburite itself abroad, the Company also export to the
various colonies the two components, as manufactured in the chemical
works, and which separately are quite non-explosive, and which, having
arrived at their destination, can be easily mixed in the proper
proportions.

Among the special advantages claimed for roburite are:--First, that it is
impossible to explode a cartridge by percussion, fire, or electric sparks.
If a cartridge or layer be struck with a heavy hammer, the portion struck
is decomposed, owing to the large amount of heat developed by the blow.
The remaining explosive is not in the least affected, and no detonation
whatever takes place. If roburite be mixed with gunpowder, and the
gunpowder fired, the explosion simply scatters the roburite without
affecting it in the least. In fact, the only way to explode roburite is to
detonate it by means of a cap of fulminate, containing at least 1 gramme
of fulminate of mercury. Secondly, its great safety for use in coal mines.
Roburite has the great advantage of exploding by detonation at a very low
temperature, indeed so low that a very slight amount of tamping is
required when fired in the most explosive mixture of air and coal gas
possible, and not at all in a mixture of air and coal dust--a condition in
which the use of gunpowder is highly dangerous.

Mr W.J. Orsman, F.I.C., in a paper read at the University College,
Nottingham, in 1893, gives the temperature of detonation of roburite as
below 2,100 deg. C., and of ammonium nitrate as 1,130 deg. C., whereas that of
blasting gelatine is as much as 3,220 deg. C. With regard to the composition
of the fumes formed by the explosion of roburite, Mr Orsman says: "With
certain safety explosives--roburite, for instance--an excess of the
oxidising material is added, namely, nitrate of ammonia; but in this case
the excess of oxygen here causes a diminution of temperature, as the
nitrate of ammonia on being decomposed absorbs heat. This excess of oxygen
effectually prevents the formation of carbon monoxide (CO) and the oxides
of nitrogen."

The following table (A), also from Mr Orsman's paper, gives the
composition of five prominent explosives, and shows the composition of the
gases formed on explosion. The gases were collected after detonating 10
grms. of each in a closed strong steel cylinder, having an internal
diameter of 5 inches.

With respect to the influence of ammonium nitrate in lowering the