The Romance of Chemistry 723 



left out of doors begins to rust, we call this a chemical change, for 

 the iron becomes something different, namely, iron oxide, with 

 quite different properties. This iron rust is not transmuted iron, 

 but iron in combination with oxygen, and that is a very different 

 thing. Chemical changes always imply a shuffling of the cards, a 

 new arrangement of partners. "Pieman + pie," as the American 

 expositor puts it, "on the one side; Boy + penny on the other 

 side." A change occurs, and the situation is "Pieman + penny" 

 and "Boy + pie." This sort of thing is going on ceaselessly all 

 the world over. It is necessary to say, however, that the boundary- 

 line between Chemistry and Physics has become very indefinite, 

 especially in light of the fact that the qualitatively chemical dif- 

 ferences between Uranium and Radium or Thorium and Radium 

 seem to depend on quantitatively physical differences in the cor- 

 puscles of electricity. 



Demonstrating the Invisible 



Many of the materials with which the chemist deals are invisi- 

 ble, and so is the air we breathe, as long as it is dry and clean. In 

 ordinary circumstances, none of us ever sees oxygen, hydrogen, 

 nitrogen, or carbon dioxide, and yet all these are as real as iron 

 and lead, sulphur and diamonds. As Professor James C. Philip 

 says: 



A gas may be without smell or taste, it may be as 

 intangible as a spirit, and as for seeing it, why> it may be off 

 and away while the observer still thinks he is looking at it. 



Now it is worth while pausing to ask how the chemist is so sure 

 about what he cannot see, why he must reject the proverb "seeing 

 is believing." 



Invisible materials betray themselves by what they do. The 

 oxygen rusts the iron; the carbon dioxide which we breathe out 

 into a beaker of lime-water makes the water cloudy ; a mouse low- 

 ered into a shaft containing the deadly carbon monoxide gas is 



