TliE STORY OF NINETEENTH-CENTURY SCIENCE 



explain with certainty just what is meant by the famil- 

 iar word soluble itself. That is to say, no one knows 

 just what happens when one drops a lump of salt or 

 sugar into a bowl of water. We may believe with Pro- 

 fessor Ostwald and his followers, that the molecules of 

 sugar merely glide everywhere between the molecules of 

 water, without chemical action ; or, on the other hand, 

 dismissing this mechanical explanation, we may say 

 with Mendeleef that the process of solution is the most 

 active of chemical phenomena, involving that incessant 

 interplay of atoms known as dissociation. But these 

 two explanations are mutually exclusive, and no one can 

 say positively which one, if either one, is right. Nor is 

 either theory at best more than a half-explanation, for 

 the why of the strange mechanical or chemical activi- 

 ties postulated is quite ignored. How is it, for example, 

 that the molecules of water are able to loosen the inter- 

 molecular bonds of the sugar particles, enabling them to 

 scamper apart ? 



But, for that matter, what is the nature of these in- 

 termolecular bonds in any case ? And why, at the same 

 temperature, are some substances held together with 

 such enormous rigidity, others so loosely ? Why does 

 not a lump of iron dissolve as readily as the lump of 

 sugar in our bowl of water? Guesses may be made to- 

 day at these riddles, to be sure, but anything like tena- 

 ble solutions will only be possible when we know much 

 more than at present of the nature of intermolecular 

 forces, and of the mechanism of molecular structures. 

 As to this last, studies are under way that are full of 

 promise. For the past ten or fifteen years Professor 

 Yan 't Hoof of Amsterdam (now of Berlin), with a com- 

 pany of followers, has made the space relations of atoms 



