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 temperature of explosion of the various substances to which it is added, it was found by a French Commission that, when dry and finely powdered, ammonium nitrate succeeds in depreciating the heat of decomposition without reducing the power of the explosive below a useful limit.  The following table (B) shows the composition of the explosives examined, and the temperatures which accompanied their explosion.