The Romance of Modern Chemistry

EXPLOSIONS AND EXPLOSIVES The fact that mercury fulminate when it decomposes produces heat is worthy of notice, for it is a phenomenon rather different from what might be expected. We have seen that as a rule the chemical combination of elements is accompanied by the evolution of heat; the process is said to be “exothermic.'” This being so, we may con- fidently anticipate that the reverse process, the decom- position of the compound into its elements, would use up heat, and therefore, if it took place spontaneously, it would be accompanied by an absorption of heat This is quite a sound conclusion, but it is obvious that mercury fulminate, the decomposition of which leads to the produc- tion of much heat, must belong to a different category. The secret of the explanation is that, although the formation of most compounds is accompanied by the evolution of heat, there are some—“ endothermic ” com- pounds, as they are called—the formation of which is accompanied by absorption of heat. In this case the reverse process, in which the compound decomposes into its constituent elements, will be accompanied by the evolution of heat So it is with mercury fulminate, which is an endothermic compound, and, like others of this class, is peculiarly liable to sudden decomposition. As a matter of fact, the explosion of mercury fulminate is accompanied by the evolution of more heat than is involved merely in the splitting of it into the constituents, for two of the elements liberated in this primary decom- position, namely, the carbon and the oxygen, immediately unite to form carbon monoxide, and as this combination is an exothermic process, the heat produced by the explosion is much augmented. The explosive disruption of the molecules of nitrogen iodide and mercury fulminate is due to the want of 168