432 DYNAMITES. 



associated with silica, alumina, magnesium carbonate, calcined 

 alum, brick-dust, tripoli, sand, boghead ashes, etc., all these 

 being substances intervening only to a slight extent, or not at 

 all, by their chemical composition, but only by their physical 

 constitution and their relative proportion. They check the 

 propagation of the molecular shocks, the harmonious succession 

 of which gives rise to the explosive wave (p. 78). After 

 deflagration, they are more or less modified. 



3. Others, containing an active base, may themselves be 

 separated into three groups. 



4. Some dynamites (those with ammonium nitrate or potas- 

 sium chlorate base) are formed by the association of nitroglycerin 

 with an explosive substance, which explodes simultaneously 

 without the elements of the one intervening chemically in the 

 decomposition of the other. They might be termed dynamites 

 with simultaneous active base. 



5. Other dynamites with simple combustible base are manu- 

 factured by taking advantage of the fact that the explosion of 

 nitroglycerin sets free a certain quantity of oxygen (3*5 per 

 cent.) in excess of that which is necessary to convert the whole 

 of the carbon into carbonic acid and the whole of the hydrogen 

 into water. 



There is then added to the nitroglycerin, whether pure or 

 already mixed with an inert substance, a certain quantity of a 

 combustible body (coal, wood sawdust, starch, straw, bran, 

 sulphur, spermaceti, etc.) for the purpose of utilising this excess 

 of oxygen. 



6. But the quantity of oxygen is generally too small for the 

 corresponding proportion of combustible matter, such as 1 per 

 cent, of coal or spermaceti, or 2 per cent, of wood sawdust, or 

 3 '5 per cent, of powdered sulphur, to be sufficient to absorb the 

 whole of the corresponding nitroglycerin. Hence in practice 

 the complementary substance must be employed in great 

 excess, which constitutes the mixed base dynamites. We will 

 only mention black dynamite, a mixture of charcoal and sand, 

 capable of absorbing 45 per cent, of nitroglycerin. Such an 

 excess of combustible matter changes the character of the 

 chemical reaction, which may cease to be a total combustion. 



7. Dynamites with a combustible explosive base may also be 

 prepared by employing as combustible complement a compound 

 explosive in itself, but which does not contain enough oxygen 

 to undergo total combustion. 



Such are gun-cotton, the several varieties of nitro-cellulose 

 and nitro-starch, picric acid, etc. 



They belong to two principal groups. 



8. (1st) Dynamites with nitrate base; such as dynamite 

 with black powder as base (100 parts of black powder associated 

 with from 10 to 50 parts of nitroglycerin). 



