8 CAEBON COMPOUNDS 



be silicon, a few compounds of which of the above type have been pre- 

 pared. 



In consequence of this unique property of carbon it is now 

 customary to place the study of carbon compounds in a separate divi- 

 sion of chemistry. To this branch of knowledge the name of organic 

 chemistry has been given, and although it is of comparatively recent 

 growth it has already attained vast dimensions. 



A very large number of the compounds present in the bodies of 

 plants and animals is made up of compounds of the four ele- 

 ments just described. Among these compounds the following are 

 important : 



1. Carbohydrates, e.g., starch and cellulose, C 6 H 10 O 5 , grape sugar, 

 C 6 H 12 O 6 , cane sugar, C 12 H 22 O n . 



2. Organic acids, e.g., acetic acid, CH 3 .COOH, oxalic acid, C.,H.j0 4 . 



3. Fats, essentially salts of glyceryl, C 3 H 5 , combined with a fatty 

 acid, e.g., stearic acid, HC 18 H 35 O 2 , oleic acid, HC^H^O*,. These 

 glyceryl salts, or glycerides as they are sometimes called, are possessed 

 of a constitution similar to the following, which represents glyceryl 

 stearate (glyceride of stearic acid, or " stearine"). 



I 

 H C 







C C ]7 H,, 

 



C 3 H 5 (C W H :8 2 ) 3 or H -C-0-C-C 17 H 35 







1 II 



H C C C 17 H, 3 



H 



4. Hydrocarbons, e.g., turpentine, C 10 H 1G . 



5. Albuminoids, containing all four of the elements in question, as- 

 sociated with small quantities of sulphur and phosphorus. The con- 

 stitution of these substances is not well known. They always contain 

 about 16 per cent of nitrogen. 



6. Amides. These also are compounds of carbon, hydrogen, 

 oxygen and nitrogen, but their structure is much less complex than 

 that of the albuminoids. A large number have been prepared, the 

 characteristic feature being that they contain the group NH 2 united 

 with an oxygen-containing compound of carbon. 



Amides may be regarded as organic acids in which the OH groups 

 have been replaced by NH. 2 . Thus acetamide, C 2 H 8 O.NH 2 , is derived 

 from acetic acid, C 2 H 3 O.OH 



H H 



H C H H C H 



I ! fH 



= C H = C N^ , 



IH 



Acetic acid. Acetamide. 



7. Amino- compounds, containing one or more NIL, groups replac- 

 ing hydrogen but not OH. 



