CLASSIFICATION OF OKGAXIC SUBSTANCES. 301 



elements are cotton, alcohol, sugar, and acetic acid composed ? How do 

 you account for the difference in their properties? 4 Jo. Show what is 

 meant by isomerism. Take acetic acid and grape sugar as examples. 

 When are substances metameric ? Give examples. 41 6. Explain isomer- 

 ism by reference to a chess-board. Why is isomerism more common in 

 organic than in mineral chemistry? 417. What are graphic formulae? 

 Illustrate by the graphic formula of water. Explain it. What is said of 

 the arrangement of atoms in the molecule ? Explain the table on page 300. 



CHAPTER XXIV. 



CLASSIFICATION OF OEGANIC SUBSTANCES. 



418. Scientific Classification. Two methods of classify- 

 ing organic bodies for the convenience of study may be 

 followed ; in one an empirical arrangement connects sub- 

 stances which are closely related in nature, and treats in 

 groups bodies possessing similarity of origin or properties ; 

 the other is a strictly scientific classification based on the 

 atomicity of the tetrad carbon. In this work we will fol- 

 low the former arrangement, prefixing it, however, with a 

 brief synopsis of the scientific method, in order to introduce 

 to you a number of bodies which would otherwise find no 

 place in the so-called natural system. Scientifically con- 

 sidered, organic bodies may be classified as follows : 



I. Hydrocarbons. 

 II. Alcohols. 



III. Ethers. 



IV. Aldehydes (and Ketones). 

 V. Acids (and Anhydrides). 



VI. Amines (including Alkaloids). 

 VII. Organo-metallic Compounds. 



This is a greatly abbreviated scheme, and does not include 

 many bodies produced in the living organism, the chemical 



