TO CORRESPONDENTS.

Poverty Bay Standard, Volume X, Issue 1125, 17 August 1882, Page 2

TO CORRESPONDENTS.

“Late Royal Enoiseer" is informed aafollows in reply to questions OUNPOWDSB Is an explosive propellent agent, consisting (as used In H.B.M.’s Service) saltpetre, 75 Sorts; sulphur, 10 parts; charcoal, 15 parts. y the burning of charcoal, the oxygen in the saltpetre becomes separated from another gas, nitrogen, with which it was previously combined, and combines with the carbon, the two forming a large volume of heated gas of great expansibility, The explosive force of gunpowder is due mainly to the audden evolution of these two heated gases (carbonic acid, and nitrogen). In a mixture of saltpetre and charcoal alone, this action is comparatively slow. Sulphur is, therefore, added to render it more rapid, an effect which it produces on account of its igniting at a much lower temperature than either saltpetre or charcoal. Gunpowder explodes at a temperature of about GOO’ Fahrenheit.

When the charge of powder la exploded In the bore of a gun, to all appearance there would seem to be an instantaneous ignition of the whole force; this, however, is i >t the case, as a certain time is necessary for the combustion of the charge. This gradual firing is of the utmost importance, for were the whole of the charge ignited instantaneously there would not be time for the action to be distributed over the particles of metal at any great distance before those in the immediate vicinity of the explosion were forced out of the action of the cohesive force, and consequently the gun, unless of enormous strength, would be burst. Pebble powder is best adapted for propellent purposes, especially in heavy guns, while the R.L.G. powder possesses the greatest expesive force. NITHO-OLYCERIXE. Glycerine is obtained from oils and fats, both vegetable and animal, by treating them with alkali, which converts the fatty acids into soap, leaving the glycerine in solution. Nitro-glycerine is obtained by the addition, very gradually, of concentrated glycerine to a mixture of the strongest sulphuric and nitric acids, in the same proportion as used in preparing gun-cotton ; the temperature being kept low by artificial means, the mixture is subsequently poured into water, which separates the nitro-glycerine; it is then collected and submitted to a long purifying process, for the purpose of separating the acids and other impurities. Nitro-glyce-rine is a most powerful explosive, of high specific gravity, and insoluble in water ; in its pure and liquid state it may, with the adoption of special precautions, be handled with safety, but it has great tendency to undergo change, and a comparatively slight incentive may then cause its violent explosion. Ono property of nitro-glycerino is that of solidifying at a temperature considerably above the freezing point of water ; it is thus comparatively little sensitive to the effects of concussion or friction, and requires to be thawed before use by application of heat, which involves additional risk of accident. The explosive force of nitro-glycerino can, in the same manner as compressed gunootton, be fully developed without any strong confinement of the charge, through the agency of a detonator. Nitro-glycerine is very valuable for some special mining operations, especially in wet or damp blastholes ; but from its dangerous nature, and the fact that its explosive power but little exceeds that of compressed gun-cotton, it is not advisable to use it for torpedo purposes, or to store it on board ships, DYNAMITE. Consists simply of sllieous, earth, or other dry powder saturated with liquid nitroglycerine, There is decidedly lose risk of accident in transporting dynamite than nitroglycerine in the pure state on account of the less liability of an escape of the substance from packages by accidental leakage, and because the efforts of concussion are somewhat deadened by its mixture witli an inert substance. It is as readily susceptible of explosion by means of detonation as is nitroglycerine ; dynamite is not so powerful an explosive agent as nitro-glycerine, but its destructive powers are very greatly in excess of gunpowder, and as it is not affected by damp or wet, it is now used very extensively for mining purposes, but it is of too uncertain a nature to be stowed with safety on board ships, and the readiness with which it freezes is a serious objection to its employment in service, as it then requires to be thawed, before use, by application of heat, which involves additional risk.

LITHO-FKAcTEirn. This compound consist-! of dynamite to which is add&l a jjil-opwtiini ni uthef i-idplvslre

material (for example, such as the constituents of gunpowder). It is of a plastic nature and is employed in the form of rolls made up in paper, which absorbs some portion of the nitro-glycerine ; its tendency to yield to pressure even when suddenly applied, renders its accidental explosion by mechanical force a matter of considerable difficulty, but there is much greater tendency to the exudation of nitro-glycerine from it than from dynamite.

This compound was discovered by Professor Abel and consists of a mixture of gun-cotton palp and saltpetre, which is then saturated witli nitro-glycerine, the granule* being covered with a coating of some impermeable material, which prevents the nitro-glycerine from being absorbeil into the system in handling, the injurious effects of which frequently produce serious results. It has been used for mining purposes, but, like all other known compounds of nitro-glycerine is not a suitable material for propellent purposes. PICRIC POWDER. This compound was also discovered by Professor Abel, and consists of a mixture of ammonium, picrate, amt saltpetre; it requires a violent blow to develop slight and partial detonation, and exhibits no tendency to ignition when submitted to very severe friction. Picric powder, when confined strongly, as in shells, exerts a destructive action less formidable than that of guncotton and nitro-glycerine, but considerably greater than that of gunpowder, and it may therefore prove a valualne substitute for the latter when greater violence of action is desired with shells of small capacity, as in the case of armour-piercing shell. Experiments have been carried on - with picric powder as a bursting charge for shells fired from guns of different calibres ranging up to the 9-inch M. L. R. gun with a charge of 4311>5. R.L.G., without a single casualty. There i» good reason, therefore, to believe it may prove to be a safe material for the bursting charge of shells. Considerable quantitie* have been recently manufactured, exactly in the same way as ordinary powder. (To be continued.)