APPENDIX 1 461 



the hydrogen. From ammonia is formed in this manner the so-called 

 chloride of nitrogen, NC1 3 , which decomposes very readily with violent explo- 

 sion on account of the evolved gases, and falls asunder as chlorine and 

 nitrogen. Out of marsh gas, or methane, CH 4 , may be obtained consecu- 

 tively, by this method, every possible substitution, of which chloroform, 

 CHC1 3 , is the best known, and carbon tetrachloride, CC1 4 , the most instruc- 

 tive. But by virtue of the fact that chlorine and bromine act, in the manner 

 shown, on the simplest typical hydrogen compounds, their action on the 

 more complicated ones may be assumed to be the same. This can be easily 

 demonstrated. The hydrogen of benzene, C ti H 6 , reacts feebly under the influ- 

 ence of light on liquid bromine, but Gustavson has shown that the addition 

 of the smallest quantity of metallic aluminium causes energetic action and 

 the evolution of large volumes of hydrogen bromide. 



If we pass on to the second typical hydrogen compound that is to say, 

 water its molecule, HOH, maybe split up in two ways : either into an atom 

 of hydrogen and a semi-molecule of hydrogen peroxide, HO, or into oxygen, 

 O, and two atoms of hydrogen, H ; and therefore, according to the principle 

 of substitution, it is evident that one atom of hydrogen can exchange 

 with hydrogen oxide, HO, and two atoms of hydrogen, H, with one atom of 

 oxygen, 0. 



Both these forms of substitution will constitute methods of oxidation 

 that is to say, of the entrance of oxygen into the -compound a reaction 

 which is so common in nature as well as in the arts, taking place at the 

 expense of the oxygen of the air or by the aid of various oxidising sub- 

 stances or bodies which part easily with their oxygen. There is no occasion 

 to reckon up the unlimited number of cases of such oxidising reactions. It 

 is sufficient to state that in the first of these oxygen is directly transferred, 

 and the position, the chemical function, which hydrogen originally occupied, 

 is, after the substitution, occupied by the hydroxyl. Thus ammonia, NH 3 , 

 yields hydroxylamine, NH 2 (OH), a substance which retains many of the 

 properties of ammonia. 



Methane and a number of other hydrocarbons yield, by substitution of 

 the hydrogen by its oxide, methyl alcohol, CH 3 (OH), and other alcohols. The 

 substitution of one atom of oxygen for two atoms of hydrogen is equally 

 common with hydrogen compounds. By this means alcoholic liquids con 

 taining ethyl alcohol, or spirits of wine, C. 2 H-,(OH), are oxidised until they 

 become vinegar, or acetic aci>d, C 2 H 3 0(OH). In the same way caustic 

 ammonia, or the combination of ammonia with water, NH 3 ,H 2 0, or NH 4 (OH), 

 which contains a great deal of hydrogen, by oxidation exchanges four atoms 

 of hydrogen for two atoms of oxygen, and becomes converted into nitric acid, 

 NO,(OH). This process of conversion of ammonium salts into saltpetre goes 

 on in the fields every summer, and with especial rapidity hi tropical countries. 

 The method by which this is accomplished, though complex, though involving 

 the agency of all-permeating micro-organisms, is, in substance, the same as 

 that by which alcohol is converted into acetic acid, or glycol, C 2 H 4 (OH) 2 , into 

 oxalic acid, if we view the process of oxidation in the light of the Newtonian 

 principles. 



But while speaking of the application of the principle of substitution to 



