8 THE DATA OF BIOLOGY. 



of the substances. With the exception of acetylene, tbu 

 various hydro-carbons are not producible by directly com- 

 bining their elements ; and the elements of most of them are 

 readily separated by heat without the aid of any antagonistic 

 affinity. Nitrogen and hydrogen do not unite with each 

 other immediately ; and the ammonia which results from 

 their mediate union, though it resists heat, yields to the 

 electric spark. Cyanogen is stable : not being resolved into 

 its components at a red heat, unless in iron vessels. Much 

 less stable however are the several oxides of nitrogen. The 

 protoxide, it is true, does not yield up its elements below a 

 red heat ; but nitrous acid cannot exist if water be added to 

 it ; hypo-nitric acid is decomposed both by water and by 

 contact with the various bases ; and nitric acid not only 

 readily parts with its oxygen to many metals, but when 

 anhydrous, spontaneously decomposes. Here it will 



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

 characteristic 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 the nitrogen contained in the nitrate of potash, yields 

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

 ton, which also contains nitric acid, is a substantially par- 

 allel phenomenon. 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-glycerin. 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 characteristic. 

 When we come hereafter to observe the part which nitrogen 



