146 



tidii for tliL' r.ipid rcdu't imi af {■ii]\\>ev oxide hy gaseous hydrogeu, but it is 

 in no sense an explanation of tlie choniical ( lianges. To explain tliese it 

 may be said tliat at I lie bigli temperature tbe molecules Iwcome unstable or 

 actually begin to decoiniiose inio the various atoms and that these then 

 combine to form molecules more stable at the temperature. The jire.sence 

 of acids makes possible the decomposition of water by electricity. The 

 ionic theory offers a satisfactory ex]ilanation. 



In contradistinction to the "contact explanation" stands the atomlc- 

 niolecular idea. It is based upon established and almost universally accep- 

 ted theories involving atoms and molecules, the relations between which 

 have been used to explain differences in properties, and to account for con- 

 stitutional and space isomerism, unsaturation and chemical activity. As- 

 suming molecules then the atoms follow as a perfectly logical deduction. 

 And if atoms they must separate from molecules as sucli during chemical 

 reactions, for in many cases there is less than a molecule of the element in 

 a molecule of the compound and even if there is they are not often united 

 in the molecule. Moreover the ionic condition of the elements necessi- 

 tates that the atoms exist at the instant of discharge of the electricity. 

 Likewise combinations must often, if not always l)e preceded by decomposi- 

 tion of molecules into the constituent atoms. The additi<)n of hydrogen to 

 nnsnturated molecules, as ethylene, must be preceded by the formation of 

 atoms of hydr((gen for these are found in dilTereni: p.arts of the new mole- 

 cule. The combination of suljihur dioxide with oxygen in the presence of 

 platinum bl.ick must be i)receded by the formation of atoms of oxygen for 

 tlie new molecule contains but ;i half molecule of oxygen and at 

 the liigli t('ni]H4-atni'(- the double molecule. S,0,;. is probably not formed. 

 Even the foi'Uiation of the molecules of water from hydrogen and 

 oxygen must be preceded by the decomposition of botli kinds of 

 niolccujcs, for in the molecule of water there is but half a molecule 

 of oxygen and tlie atoms of hydrogen arc not united to each other. 

 'Hie combination nf annnonia with hydr()gcn chloride may be c-ited as 

 another example for the hydi'ogeu and chlorine are not iniited in annno- 

 niiuu chloride. It is doubtful il an.\ molecules as such ever have any 

 tendency to combiu(> or to iuti>r;icl in .iny way. The conditions luider which 

 m;itei'ial is jilaced in ordei' to stinnilale chendcal ;iction is concei\'ably for 

 the pnrpo.sc of starting the decom|>osilion oi" niolccnies into atoms which 

 by coniliining evolve th" energy to conlinne (he decom[)(>sltlon. The ther- 



