10 BOEDER LINES OF KNOWLEDGE 



try. It has shown us how bodies stand affected to 

 each other throuojh an almost boundless range of com- 

 binations. It has given us a most ingenious theory to 

 account for certain fixed relations in these combina- 

 tions. It has successfully eliminated a great number 

 of proximate compounds, more or less stable, from or- 

 ganic structures. It has invented others which form 

 the basis of long series of well-known composite sub- 

 stances. In fact, we are perhaps becoming overbur- 

 dened with our list of proximate principles, demon- 

 strated and hypothetical. 



How much nearer have we come to the secret of 

 force than Lully and Geber and the whole crew of 

 juggling alchemists ? We have learned a great deal 

 about the how^ what have we learned about the why ? 



Why does iron rust, while gold remains untarnished, 

 and gold amalgamate, while iron refuses the alliance of 

 mercury ? 



The alchemists called gold Sol, the sun, and iron 

 Mars, and pleased themselves with fancied relations 

 between these substances and the heavenly bodies, by 

 which they pretended to explain the facts they ob- 

 served. Some of their superstitions have hngered in 

 practical medicine to the present day, but chemistry 

 has grown wise enough to confess the fact of absolute 

 ignorance. 



What is it that makes common salt crystallize in the 

 form of cubes, and saltpetre in the shape of six-sided 

 prisms ? We see no reason why it should not have 



