1886.] Conduction and Molecular Composition, fyc. 289 



If a clear distinction can be drawn — as I suppose it can — between 

 simple and composite electrolytes, the presence of a member of the 

 latter class will probably be found to be essential to the occurrence of 

 many interactions taking place at moderate temperatures ; thus the 

 oxidation of iron, which is generally supposed to take place only in 

 moist air, is doubtless dependent, not merely on the presence of water, 

 but of impure water — of water rendered conducting by association 

 with foreign matters ; similarly it may be expected that zinc will be 

 found to have no action on water even when associated with a less 

 positive metal, and it would doubtless have no action on sulphuric 

 acid, if such a compound were obtainable in a pure state; but a 

 mixture of sulphuric acid and water readily dissolves it, as the two 

 together form a composite electrolyte of comparatively low resistance. 



It can scarcely be doubted that when our elements or compounds 

 are resolved into their ultimate atoms, these atoms are capable of 

 directly uniting, and that no catalyst is then required. But if this be 

 the case, and if, as I suppose, the atoms rarely saturate each other, 

 the direct union of compounds should also be possible in cases in 

 which there is considerable residual affinity ; such union would not 

 involve a separation from each other of the constituent elements of 

 one or both of the interacting bodies such as takes place in the 

 changes previously considered. Union of two molecules having 

 taken place ; the elements of the interacting bodies having thus been 

 brought into intimate association : it is very probable that in many 

 cases intramolecular change will then supervene, resulting sometimes 

 in mere atomic redistribution, at other times in the resolution of the 

 complex molecule into simpler molecules. I am inclined to think that 

 the majority of so-called double decompositions are thus brought 

 about. 



The union of sulphuric anhydride with water to form sulphuric 

 acid, and of sulphuric acid with water to form hydrates, are doubtless 

 cases of this kind. The formation of the hydrate S03*OH 2 must be 

 supposed to be immediately followed by the occurrence of atomic 

 redistribution if we accept the current view that sulphuric acid is a 

 hydroxide of the formula S0 2 (OH) 2 ; whether after the formation of 

 the hydrate 112804*0112 has taken place atomic redistribution in like 

 manner supervenes is a moot point ; the large amount of heat de- 

 veloped by the interaction of water and sulphuric acid is, however, 

 specially noteworthy. 



Sodium hydroxide is universally regarded as the analogue of water : 

 is its action on sulphuric acid analogous to that of water ? I certainly 

 am inclined to hold that it is, and that in the first instance an aggre- 

 gate, NaHO*S04H 2 , results, owing to the attraction of the oxygen of 

 the hydroxide by the oxygenated radicle of the acid : atomic redistri- 

 bution thereupon takes place, and either the molecule is resolved into 



