Detonations are obtained from nitro-glycerine, gun-cotton, &c., by exploding with fulminate of mercury. They state that fulminate of mercury does not detonate gunpowder; but if the exploding charge is a small amount of nitro-glycerine, itself detonated by fulminate of mercury, then an explosion of the first order is obtained. The relative effects were approximately measured by determining the quantities necessary to rupture small cast iron shells of supposed equal strength. _Results of their Experiments._--The following are some of the results:-- +---------------+---------------------------+ | | Explosive Effect. | | +---------------------------+ | | 2nd Order. | 1st Order. | +---------------+-------------+-------------+ |Gunpowder | 1·00 | 4·34 | |Gun-cotton | 3·00 | 6·46 | |Nitro-glycerine| 4·80 | 10·13 | +---------------+-------------+-------------+ According to the above table, nitro-glycerine is more than ten times, and gun-cotton more than six times, as powerful as gunpowder fired in the ordinary way (2nd order). The want of reciprocity between two detonating agents is shown in a remarkable degree by the following experiments, carried out by Professor Abel:-- 1.--The detonation of 1/4 ounce of gun-cotton (the smallest quantity that can be thus applied) induced the simultaneous detonation of nitro-glycerine, enclosed in a vessel of sheet tin, and placed at a distance of 1 inch from the gun-cotton. 2.--The detonation of 1/2 ounce of gun-cotton produces the same effect with an intervening space of 3 inches between the substances. 3.--The detonation of 2 ounces of nitro-glycerine in _close contact_ with compressed gun-cotton failed to accomplish the detonation of the latter, which was simply dispersed in a fine state of division, in all the instances but one, in a large number of experiments. Explosive agents are divided into explosive mixtures and compounds. In the former the ingredients are mechanically mixed, and can be separated by mechanical means. In the latter the ingredients are chemically combined, and can only be separated by chemical change. _Torpedo Explosive Agents._--The explosive agents that are practically the most important, as far as their employment as torpedo charges are concerned, are as follows:-- _Explosive Mixtures._--A.--Explosive mixtures. 1.--Gunpowder. } Nitrate class 2.--Ammonium picrate, or picric powder. } _Explosive Compounds._--B.--Explosive compounds. 1.--Nitro-glycerine. 2.--Dynamite (No. 1). 3.--Gun-cotton. 4.--Fulminate of mercury. A.--EXPLOSIVE MIXTURES. _Gunpowder._--This explosive mixture is composed of seventy-five parts of nitre (saltpetre), fifteen parts of charcoal, and ten parts of sulphur.