On being ignited, the oxygen which is feebly held by the nitrogen combines with the carbon, forming carbonic oxide gas, whilst the sulphur unites with the potassium of the nitre, the whole combination being accompanied by a great evolution of heat and expansion of gas, and the nitrogen is set free. _Properties, &c._--A spark, friction between hard bodies, or a temperature of 572° F., are any of them sufficient to cause an explosion of gunpowder. Slight moisture, due to damp air, &c., produces caking and deterioration. Wetting causes permanent destruction. Frost does not injure it. It can be fired by ordinary methods. It can be transported and handled with safety and great ease. It is not a suitable explosive agent for torpedoes, on account of its liability to be injured by damp, as well as its not being sufficiently violent, though for the sake of convenience, &c., it is often employed for such work. The effect produced by the explosion of a charge of gunpowder, ignited by the ordinary method, is that of an uplifting rather than a shattering effect. This evil may be greatly remedied, when gunpowder is used as the charge of a torpedo, by firing it with a detonator, by which means its fullest explosive effect is developed. _Picric Powder._--The picrates are salts of picric acid. Picric acid is formed by the action of nitric acid on carbolic acid. The picrate employed by Professor Abel is prepared from picric acid and ammonium. This preparation, or salt mixed with nitre (saltpetre), forms Abel's picric powder. _Properties, &c._--It is prepared for use in a similar manner to gunpowder, and it can be handled in the same way. It is less violent than dynamite or gun-cotton, though much more so than gunpowder. It is difficult to explode it by blows or friction. If flame be applied to it, the part touched burns, but the combustion does not become general. This explosive agent will probably be used for spar torpedoes, when gun-cotton or dynamite are not employed. B.--EXPLOSIVE COMPOUNDS. _Nitro-glycerine._--Nitro-glycerine is formed by the action of nitric acid upon glycerine at a low temperature. The manufacture of this compound consists, first, in the slow mixture of the glycerine with the acid, at a low temperature; secondly, in washing the nitro-glycerine from the excess of acid with water. The nitric acid before use is mixed with a certain proportion of strong sulphuric acid, so that the water formed during the reaction may be taken up, and thus any dilution of the nitric acid is prevented. Nitro-glycerine is composed of carbon, hydrogen, nitrogen, and oxygen, as indicated by the equation _C_{3}H_{5}N_{3}O_{9}_. _Properties, &c._--At ordinary temperatures nitro-glycerine is an oily liquid, having a specific gravity of 1·6. Freshly made it is creamy white and opaque, but clears and becomes colourless on standing for a certain time, depending on the temperature.