MODERN EXPLOSIVES 21 



heavier guns were introduced, a large grain powder which 

 burned more slowly was adopted, but further increase in 

 the size of the guns led to the introduction of pebble 

 powders, which in some cases consisted of cubes of over an 

 inch ' side. Such cubes having large available surface 

 evolved the usual gases in greater quantity at the start of 

 the combustion than toward the finish, since the surface 

 became gradually smaller, thus causing extra strain on the 

 gun as the projectile was only just beginning to move. 

 General Rodman, an American officer, introduced prism 

 powder to overcome this difficulty, the charges being built 

 up of perforated hexagonal prisms in which combustion 

 started in the perforations and proceeding, exposed more 

 surface, the prisms finally breaking down into what was 

 virtually a pebble powder. 



In order to secure still further control over the pressure, 

 modifications in the proportions of the ingredients became 

 necessary; the diminution of the sulphur and increase of 

 the charcoal causing slower combustion, and moreover the 

 use of charcoal prepared at a low temperature giving the 

 so-called "cocoa powders." 



The products of the combustion of powder and its manner 

 of burning are largely influenced by the pressure, a property 

 well illustrated by the failure of a red-hot platinum wire to 

 ignite a mass of powder in a vacuum, only a few grains 

 actually in contact with the platinum undergoing combus- 

 tion. The gaseous products obtained are carbon dioxide, 

 carbon monoxide, and nitrogen, other products being potas- 

 sium carbonate, sulphate, and sulphide. The calculated 

 gas yield per gram at C. and 760 mm. pressure is 264-6 

 c.c., while Nobel and Abel actually obtained by experiment 

 263-74 c.c., numbers agreeing very closely. At the tem- 

 perature of explosion this volume is enormously increased. 



In 18'32, Braconnot found that starch, ligneous fiber, and 

 similar substances, when treated with strong nitric acid 

 yielded exceedingly combustible substances, and Pelouze, in 

 1838, extended the investigation to cotton and paper. 



