PROBLEMS OF CHEMISTRY 321 



are called ions. This idea has thrown a great deal of light 

 upon important problems of chemistry, but it has suggested 

 many new ones Some substances for example, sugar 

 do not act like salt when dissolved in water. Why this 

 difference ? Then, too, some liquids which are good solvents 

 do not act at all like water. What is it in water that dis- 

 tinguishes it from most other liquids, such as alcohol and 

 ether, enabling it to tear many substances asunder? These 

 are questions that are now very much to the front. Rapid 

 progress is being made, and we may look for important 

 discoveries in this field in the near future. 1 



1 This article was first published in 1901. The reader may profit- 

 ably consider the dates of discoveries and investigations that are 

 given in this book. He will see how active and varied have been the 

 efforts of scientists, in recent years especially, to solve the problems 

 of Nature, how ingenious have been their methods of attack, and how 

 with the solution of each one the field broadens and the new prob- 

 lems become more difficult and more fascinating. ED. 



