364 CHEMISTRY. 



pulverization ? 503. How does lime differ from most other manures in its 

 action? Give the maxim in regard to lime, and the ground for it. 504. 

 What is marl ? What is said of its effects on soils ? 505. Give the anec- 

 dote of Franklin in regard to gypsum. What is said of the manner in 

 which gypsum acts as a fertilizer ? 506. What is said of vegetable refuse ? 

 507. What of sewer-water? 



CHAPTER XXIX. 



OILS AND FATS. 



508. Acids. The common idea that acids are sour bodies 

 must now be given up, for under this head are included 

 many oily and fatty substances which do not react acid 

 at all. The sources of organic acids are exceedingly vari- 

 ous; thus formic acids can be extracted both from red 

 ants and from nettles ; acetic acid is a product of fermen- 

 tation, as you will learn in the next chapter ; butyric acid 

 is contained in rancid butter, palmitic acid in palm-oil, 

 stearic acid in tallow, and melissic acid in beeswax. These 

 form part of a series called the Fatty Acid Series.* The 

 first one is a liquid, with a low boiling-point ; the rest in- 

 crease in density, becoming oily and finally solid. The 

 first acids of this series mix with water, but the last acids 

 are quite insoluble in water; thus a gradual transition of 

 properties is noticeable, and their formulae become heavier 

 and more complex as you ascend the series. Formic acid 

 is CH 2 O 2 , acetic acid C 2 H 4 O 2 , etc., while the last named, 

 melissic acid, has the formula C 30 H 60 O 2 . 



There are many other acids which do not belong in this 

 series, also derived from various sources ; thus tartaric acid 



* See last column in Table on page 303. 



