SPONTANEOUS DECOMPOSITION. 437 



explosion immediately occurred, eighty persons being killed 

 or wounded. 



Moreover, thawing may occasion exudations of pure nitro- 

 glycerin, the latter expanding by the fact of solidification. It 

 is thus exposed and may explode by subsequent shock of friction. 

 It is sometimes enough to bring about an accident, to cut a 

 frozen cartridge with an iron tool. Ramming is even dangerous 

 with it. Moreover, frozen dynamite has not lost the property 

 of exploding by influence. 



7. Action of heat. Dynamite, submitted to the action of a 

 gentle heat, undergoes no change, even under the prolonged 

 influence (an hour) of a temperature of 100. Heated rapidly, 

 it takes fire near 220, like nitroglycerin. If ignited, it burns 

 slowly and without exploding ; but if it be enclosed in a 

 hermetically sealed vessel with resisting walls, it explodes under 

 the influence of heating. The same accident is sometimes pro- 

 duced in the inflammation of a large mass of dynamite, owing to 

 the progressive heating of the interior parts, which brings the 

 whole mass to the temperature of explosive decomposition. 



Dynamite, moreover, becomes more sensitive to shock, as do 

 also explosive substances in general, according as it is raised 

 nearer to temperature of decomposition. 



Direct solar light can cause a slow decomposition, as with all 

 the nitro and nitric compounds. Electric sparks, generally 

 speaking, ignite dynamite without exploding it, at least when 

 operating in the open air. 



8. Spontaneous decomposition. Dynamite prepared with 

 neutral nitroglycerin appears to keep indefinitely if care be 

 taken to add to it a small quantity of calcium carbonate, or 

 alkaline bicarbonate, thoroughly mixed. Contact with iron and 

 moisture changes it in course of time. Dynamite which has 

 commenced to undergo change becomes acid and sometimes 

 explodes spontaneously, especially if contained in resisting 

 envelopes. Nevertheless, neutral and well-prepared dynamite 

 has been kept for ten years in a magazine without loss of its 

 explosive force. 



9. Action of water. Water brought into contact with 

 dynamite gradually displaces the nitroglycerin from the silica. 

 This action is slow but inevitable. It tends to render all wet 

 dynamite dangerous. However, ordinary dynamite hardly 

 attracts the atmospheric moisture. 



It has been observed that a dynamite made with wood saw- 

 dust can be moistened, then dried without marked alteration, 

 provided the action of the water has not been too prolonged. 

 Fifteen to twenty per cent, of water may be added to cellulose 

 dynamite, rendering it insensible to the shock of a ball without 

 depriving it of the property of exploding by a strong fuse. But 

 nitroglycerin is then separated under a slight pressure. 



