146 



tion for the rnjiid i-eduetion of copper oxide by gaseous hydrogen, but it is 

 iu uo sense an exphmation of the chemical clianges. To explain these it 

 may be said that at the high temperature the molecules become unstable or 

 actually begin to decojnjiose into the various atoms and that these then 

 combine to form molecules more stable at the temperature. Tlie presence 

 of acids makes possil>le the decomposition of water by electricity. Tlie 

 ionic theory offers a satisfactory exiilanation. 



In contradistinction to the '•contact explanation" stands the atomic- 

 molecular idea. It is based upon estaljlished and almost universally accep- 

 ted theories involving atoms and molecules, the relations between which 

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

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

 sunn'ng molecules then the atoms follow as a i)erfectly logical deduction. 

 And if atoms they must separate from molecules as sut-h during chemical 

 reactions, for in many '-ases there is less than a molecaile of the element in 

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

 iu 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 be preceded by decomposi- 

 tion of molecules into the constituent atoms, 'riic addition of hydrogen to 

 misatnrated molecules, as ethylene, nui.st be pitMcdcd liy tlic formation of 

 atoms of hydrogen for these are found in different ]i,irts of tlie new mole- 

 cule. The combination of suliihur dioxide with oxygen in the pi'eseuce of 

 l»latinum black must be preceded l)y the formation of atoms of oxygen f(»v 

 the new molecule contains but a half ntolecule of oxygen and at 

 the high temjicrature tlie double molecule. SX),;. is pi-obably not formed. 

 Even the formation ()f the molecules of water from hydrogen and. 

 oxygen must be preceded by the decomposition of i)oth kinds of 

 molecules, for in the molecide tif water there is but half a molecule 

 of oxygen and the atoms of hydrogen are not luiited to eacji other. 

 The combination of annnonia with hydrogen chloride may l)e cited as 

 another exanuih> for the hydrogen and chlorine are not united in annno- 

 nium chhu'ide. It is doubtful if any molecules as such ever have any 

 tendency to combine or to interact in any way. The conditions under which 

 material is placed in f)rder to stinuilate chemical action is conceivably for 

 tlie purpose of starting the decomposition of molecules into atoms whicli 

 by combining evolve the energy to continue tl<e decomposition. The ther- 



