46 



plosive and the rapidity of firing may be varied at will, and is 

 regulated by the following physical properties. 



(i) The density of the powder, (2) the hardness, (3) the 

 size of the grains or pieces, (4) the shape of the grains, (5) 

 the amount of glaze or facing imparted to the powder. 



Before me are specimens of English military powders, 

 the grains ranging in size from large prisms for heavy guns, 

 to fine dust powder for small arms, the shape, size, etc., as 

 mentioned above, being adapted to the use for which the 

 powder is intended. 



The advantages of powder over other explosives are — 

 (i) The rate of combustion is gradual, compared with 

 most explosives, and by varying the mechanical 

 ' . processes of manufacture, can be modified so as 



to suit every kind of weapon. 



(2) The ingredients are easily procured. 



(3) They are comparatively cheap. 



(4) Powder with proper precautions is safe in manu- 



facture, store and transport ; it also keeps well. 

 Its disadvantages are — 



(i) Large waste of effect, caused by formation of 60 

 per cent, solid products of explosion. 



(2) Heating of gun, owing to contact with this solid 



residue at high temperature. 



(3) Spoilt by exposure to rain or damp (the nitre being 



dissolved out). 



Two other explosive mixtures deserve attention. 



(i) White Gunpowder, a mixture of Chlorate of Potash, 

 Sugar, and Ferrocyanide of Potassium. A few grains of this 

 powder placed on an anvil detonates violently when struck 

 with a hammer. 



(2) A mixture of Chlorate of Potash and Sugar, which is 

 fired by merely touching it with a glass rod moistened with 

 strong Sulphuric Acid. 



The most sensitive example of an explosive compound is 

 Iodide of Nitrogen^— a dark brown powder, obtained by 

 treating, with certain precautions, Iodine with Ammonia. 



