1889.] on an attempt to apply to Chemistry, d'c. 515 



metallic aluminium causes energetic action, and the evolution of 

 large volumes of bromide of hydrogen, 



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

 to say water, its molecule, HOH, may be split up in two ways : either 

 into an atom of hydrogen and a molecule of oxide of hydrogen, HO, 

 or into oxygen, 0, 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 oxide of hydrogen, 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 com- 

 pound — 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 substances or bodies which part easily 

 with their oxygen. There is no occasion to reckon uj) 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^, yields hydroxylamine, NH-(OH), a substance which retains 

 many of the jDroperties of ammonia. 



Methane and a number of other hydrocarbons yield, by substi- 

 tution of the hydrogen by its oxide, methylic, CH^(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 containing ethyl alcohol, or spirits of wine, 

 C^H^(OH), are oxidised till they become vinegar or acetic acid, 

 C^H^O(OH). In the same way caustic ammonia, or the combination 

 of ammonia with water, NH^H'-O, or NH-^(OH), which contains a great 

 deal of hydrogen, by oxidation exchanges four atoms of hydrogen for 

 two atoms of oxygen, and become converted into nitric acid NO-^(OH). 

 This process of conversion of ammonia salts into saltj)etre goes on 

 in the fields every summer, and with especial raj^idity in 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-H'^(OH)'', 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 substi- 

 tution to water, we need not multiply instances, but must turn our 

 attention to two special circumstances which are closely connected 

 with the very mechanism of substitutions. 



In the first place, the replacement of two atoms of hydrogen by 

 one atom of oxygen may take j^lace in two ways, because the hydrogen 

 molecule is comj)osed of two atoms, and therefore, under the influence 

 of oxygen, the molecule forming water may separate before the oxygen 

 has time to take its place. It is for this reason that we find, during 



