and on Dissociation, 449 



general, the oxides of the precious metals, &c. ; sometimes, even, 

 these decompositions are accompanied by a sudden disengage- 

 ment of heat, as is the case with the chloride, iodide, and 

 sulphide of nitrogen. 



Decompositions which are attended with disengagement of 

 heat are evidently an exceptional case, and embarrassing even to 

 some of the most plausible theories of chemical combinations. 

 They characterize in a general manner the compounds of nitro- 

 gen, which are never formed directly, or by the simple and 

 immediate contact of their elements. The accuracy of this 

 observation is evident for the majority of explosive nitrogenized 

 substances, which are resolved into simple bodies at the moment 

 of their destruction. But for non-explosive nitrogen compounds, 

 it may be deduced from this important fact, which is confirmed 

 by MM. Favre and Silbermann, that protoxide of nitrogen in 

 the phenomena of combustion which it produces, developes more 

 heat than the oxygen which it contains would furnish if burnt 

 alone. It is clear that protoxide of nitrogen, and therefore other 

 compounds of the same class, disengage heat at the moment of 

 their destruction. 



If two combustion experiments are made with the same quan- 

 tities of potassium and sulphur, employing in succession crystal- 

 lized octahedral sulphur and soft sulphur, the latter will disengage 

 a larger quantity of heat than the octahedral sulphur, and the 

 difference will be precisely equal to the quantity of heat observed 

 by M. Itegnault when he heated soft sulphur to 92°, and observed 

 its temperature spontaneously rise to 110°. The quantity of heat 

 latent (this is the term used, but it ought to be altered) or dis- 

 simulated in the sulphur, maintains an unstable equilibrium. It 

 may be assumed that in this respect sulphur, protoxide of 

 nitrogen, and the fulminating compounds of nitrogen are con- 

 stituted in the same manner ; and it is at the moment at which 

 this unstable equilibrium is broken by the influence of the heat 

 itself that the calorific effect shows itself in the experiments of 

 MM. Eegnault, Favre and Silbermann, and in the destruction 

 of the fulminating compounds of nitrogen. 



On the other hand, my brother has shown how considerable 

 is the influence of temper on the properties of sulphur. Besides 

 soft sulphur, which was well known, and which only differs 

 from ordinary sulphur by its physical properties, he discovered 

 insoluble sulphur, which is distinguished from all the rest by a 

 chemical property — insolubility in bisulphide of carbon. This 

 modification has been obtained without the intervention of any 

 other cause than the sudden change of temperature by which 

 the phenomenon of temper is produced in steel and in explosive 

 Dutch drops. It is therefore certain that, by tempering or sudden 



