140 The Evolution of 



us. He begged the chemists to stay their researches for a 

 little while that he might get a chance to complete his book. 

 But they did not stop ; and now if Leopold Gmelin were alive 

 he would find it not only impossible to finish such a book, 

 but almost impossible to write down the facts as rapidly as 

 discovered. No mortal now lives Avho can master all the 

 minute particulars of organic chemistry. The only way to 

 keep abreast of the times is to learn the principles of these 

 facts. They are all principles of the actions and inter- 

 actions of atoms. The way the carbon compounds are 

 chained together enables the forgetful chemist with a mini- 

 mum of effort to recall forgotten formulas. For instance, 

 having forgotten the formula of alcohol, he can readily re- 



construct it thus : To four-bonded carbon (-C-) he adds 



H ' 

 four hydrogen atoms, forming methane (H-C-H),twomole- 



ik 



cules of which being united, after releasing a bond in 



each, gives ethane (H-C-C-H), and finally adding hydroxyl 



Hlk 

 (H-0-), after removing a terminal hydrogen, we get ethyl 



hydrate or alcohol (H-C-C-0-H). The points to remem- 



HH 



ber are that it is a hydrate and the second of the series. 

 Let an atom of oxygen replace two hydrogens in alcohol, 



55 



and we have acetic acid (H-C-C-0-H). From marsh gas 



H 



through kerosene oil and vaseline to paraffin or min- 

 eral wax we have hundreds .of substances that only differ 

 from each other in an additional =CH 2 group to ethane 



55 tiHH 333? 



(H-C-C-H,then H-C-C-C-H, then H-C-C-C-C-H, etc.). 



i A H H H HHHli 



Their hydrates give many alcohols, and the acids, as well 

 as other substances that can be formed along the same line, 



