DECOMPOSITION OF ORGANIC COMPOUNDS. 461 



by replacement of the hydrogen of carboxyl by alcoholic radicals. 

 For instance : 



Q . CH 3 CO\ C 2 H 5 \ H\ 



C C ~ h 



H/ ~ CH 3 CO/ 

 Ethyl alcohol. Acetic acid. Acetic ether. Water. 



The various fats belong to this group of compound ethers. 



7. Carbohydrates. (Sugars, starch, cellulose, etc.) These are 

 compounds of carbon, hydrogen, and oxygen, in which the number 

 of carbon and oxygen atoms is the same, while the number of 

 hydrogen atoms is double that of the oxygen atoms. As the hydro- 

 gen and oxygen are present in the proportion to form water, they are 

 hence called carbohydrates. There are only a few exceptions to the 

 above statement. Most carbohydrates are capable of fermentation, 

 or of being easily converted into fermentable bodies. Instances : 

 C 6 H 12 6 , C 6 H I0 5 , etc. 



Glucosides are substances the molecules of which may be split up 

 in such a manner that several new bodies are formed, one of which 

 is sugar. 



8. Amines and amides. Substances formed by replacement of 

 hydrogen in ammonia by alcohol or acid radicals. For instance : 

 ethyl amine, NH 2 .C 2 H 5 , urea, N 2 H 4 .CO, etc. The alkaloids belong 

 to this group. 



9. Cyanogen and its compounds. Substances containing the radical 

 cyanogen, CN. For instance : potassium cyanide, KCN. 



10. Proteins or albuminous substances. These, besides carbon, 

 hydrogen, and oxygen, always contain nitrogen and sulphur, some- 

 times also other elements. Instances : albumin, casein, fibrin, etc. 



In connection with each of these groups have to be considered the 

 derivatives obtained from them directly or indirectly. 



As all those organic compounds the constitution of which has 

 been explained may be looked upon as derivatives of either methane, 

 CH 4 , or benzene, C 6 H 6 , a separation of organic compounds is made 



QUESTIONS. Explain the term residue or radical. What is understood by 

 the expression chain, when used in chemistry? What are the characteristics 

 of an homologous series ? Give an explanation of the terms isomerism, meta- 

 merism, and polymerism. How does heat act upon organic compounds? 

 What is destructive distillation? State the difference between combustion, 

 decay, fermentation, and putrefaction ; what is the nature of these processes, 

 and under what conditions do they take place? How do chlorine, nitric acid, 

 and alkalies act upon organic substances ? What is the action of hydrogen 

 and of dehydrating agents upon organic substances ? Mention the chief 

 groups of organic compounds. 



