76 



HOW CROPS GROW. 



It is to be observed that these fatty acids make a nearly 

 complete series, the first of which contains one carbon 

 and two hydrogen atoms, and the last 27 carbon and 54 

 hydrogen atoms, and that each of the intermediate acids 

 differs from its neighbors by CHg. The first two acids 

 in this series are thin, intensely sour, odorous liquids 

 that mix with water in all proportions ; the third to the 

 ninth inclusive are oily liquids whose consistency in- 

 creases and whose sourness and solubility in water dimin- 

 ish with their greater carbon content. The tenth and 

 other acids are at common temperatures nearly tasteless, 

 odorless, and fatty solids, which easily melt to oily liquids 

 whose acid properties are but feebly manifest. Of these 

 acids a few only require further notice. 



Acetic Acid, C2H4O2, or CHsOOOH, formed in the 

 " acetic fermentation " from cider, malt, wine and whis- 

 ky, alcohol being in each case its immediate source, 

 exists free in vinegar to the extent of about 5 per cent. 

 When pure, it is a strongly acid liquid, blistering the 

 tongue, boiling at 246°, and solidifying at about 60° to a 

 white crystalline mass. In plants, acetic acid is said to 

 exist in small proportion, mostly as acetate of potassium. 



Butyric Acid, C^HsOj, or CHaCH^OHjOOOH, in the 

 free state, occurs in rancid butter, whose disagreeable 

 odor is largely due to its presence. In sweet butter it 

 exists only as a glyceride or fat of agreeable qualities. 



