SPONTANEOUS DECOMPOSITION. 45 



pretation of the effects of tamping, as has been said before 

 (pp. 40, 41). 



It is, further, in this way that every fusing substance may be 

 transformed into a detonating substance, when the mass of it 

 contained in a given capacity is increased, of course without 

 any change being made either in the orifices or the form of the 

 capacity. 



The difference between the various modes of decomposition 

 of an explosive substance, according as its mass is more or less 

 considerable, deserve particular attention, for it is continually 

 occurring in practice. 



2. This is noticeable even when there is an escape for the 

 gases of the explosion, provided the explosive mass be large 

 enough. It is thus that the decomposition of a fusing sub- 

 stance, taken at constant weight, and contained within a given 

 capacity, may change into explosion, when the orifice of this 

 capacity is contracted in such a manner that the inward pressure 

 and temperature may increase beyond a certain limit. 



3. The same remark applies to spontaneous decomposition of 

 great masses of matter. Slow at first at the ordinary tempera- 

 ture, they quicken under the influence of that very increase in 

 temperature to which they themselves give rise. It may also 

 happen that this rise in temperature changes the character of 

 the decomposition by causing a fresh reaction after the initial 

 one, throwing off more heat. The rise in the temperature of 

 the mass hence still further increases, even to the extent of 

 producing a tumultuous reaction, and a general explosion. 



4. These facts, often observed in laboratories, have been 

 quoted to account for the spontaneous explosions of gun-cotton 

 and nitroglycerin, and their tendency is to cause us to regard 

 as especially dangerous any explosive substance in which the 

 process of decomposition has commenced. 



5. These considerations demonstrate the cause of general 

 explosions, not only of explosive substances contained in very 

 solid vessels, but even in vessels whose resistance is very slight, 

 such as wooden cases or thin metallic envelopes, and again of 

 explosions of substances piled up in the open air when the 

 accumulation of these substances permit of a rise in the 

 temperature and of a gradual acceleration in the reaction 

 (see p. 41). 



6. General explosions may also occur with substances divided 

 into very small quantities, if these small quantities are 

 sufficiently close to one another to constitute a large mass in 

 the aggregate, and if the mechanical effects admit of accumula- 

 tion and to produce a common result. 



The precautions, therefore, both for storage and use, should be 

 taken just as though all the individual portions of the explosive 

 substance were collected into one single mass. Herein lie the 



