THE BEGINNINGS OF LIFE. 85 



hydrogen, oxygen, and nitrogen show the least atomic 

 cohesion of all elements. And while oxygen displays, 

 alike in the range and intensity of its affinities, a 

 chemical energy exceeding that of any other substance 

 (unless fluorine be considered an exception), nitrogen 

 displays the greatest chemical inactivity 1 . Now on 

 calling to mind one of the general truths arrived at 

 when analyzing the process of Evolution in general, 

 the probable significance of this double difference will 

 be seen. It was shown ("First Principles," 123) that, 

 other things equal, unlike units are more easily se- 

 parated by incident forces than like units are that 

 an incident force falling on units that are but little 



1 Hence its compounds are generally most unstable. ' Here it will 

 be well to note, as having a bearing on what is to follow, how charac- 

 teristic of most nitrogenous compounds is this special instability. In 

 all the familiar cases of sudden and violent decomposition, the change is 

 due to the presence of nitrogen. The explosion of gunpowder results 

 from the readiness with which nitrogen contained in the nitrate of 

 potash yields up the oxygen combined with it. The explosion of gun- 

 cotton, which also contains nitric acid, is a substantially parallel pheno- 

 menon. The various fulminating salts are all formed by the union with 

 metals of a certain nitrogenous acid called fulminic acid ; which is so 

 unstable that it cannot be obtained in a separate state. Explosiveness 

 is a property of nitro-mannite, and also of nitro-glycerine. Iodide of 

 nitrogen detonates on the slightest touch, and often without any assign- 

 able cause. Percussion produces detonation in sulphide of nitrogen. 

 And the body which explodes with the most tremendous violence of any 

 that is known, is the chloride of nitrogen. Thus these easy and rapid 

 decompositions, due to the chemical indifference of nitrogen, are charac- 

 teristic. When we come hereafter to observe the part which nitrogen 

 plays in organic actions, we shall see the significance of this extreme 

 readiness shown by its compounds to undergo change.' Spencer, loc. 

 cit. p. 8. 



