48 ORGANIC AGRICULTURAL CHEMlbiRY 



The same general relations in their physical properties exist 

 between the successive members of the acid series as were 

 found in the case of the hydrocarbons, alcohols and other 

 homologous series. The lower members are liquids easily dis- 

 tilled, the intermediate members are heavier, not easily volatile 

 liquids, while the higher members are non-volatile solids. The 

 lower members are soluble in water; the higher members are 

 not soluble in water, but are usually soluble in alcohol. 



Formic Acid 



Formic acid is found free naturally in certain ants, bees and 

 nettles. It is a water-like liquid with a very sharp, irritating 

 odor. It produces blisters on the skin. In ants and bees it is 

 used as a poison in killing their prey. 



EXPERIMENT STUDY XI 



Formic Acid 



Note. — In testing the action of acids on indicators proceed as 

 follows: (a) Test the acid with blue litmus paper, {b) To i.o c.c. 

 of acid add lo c.c. water, and then 2 drops of phenolphthalein solution. 

 Add KOH or NaOH drop by drop until the color changes. 



(i) Test formic acid for color, odor, action toward litmus and phe- 

 nolphthalein. (2) Shake up about i.o g. of mercuric oxide with 2 

 or 3 c.c. of acid plus an equal volume of water. After 5 minutes 

 filter and heat the filtrate in a test tube connected with delivery tube 

 which is immersed in another tube containing a little limewater. 

 What gas is evolved? What is the residue? The reaction is as 

 follows : 



2 H-COOH + HgO -> (H-C00)2Hg -f- H2O 

 Formic acid Mercuric formate (soluble) 



2 (H-C00)2Hg + heat -> 2 H-COOHg + CO2 -1- HC-OOH 



Mercurous formate (insoluble) 

 2 H-COOHg -}- heat -> 2 Hg -f- CO2 + H-COOH 



(3) Dilute 2 c.c. formic acid with an equal volume of water. Add a 

 few drops of dilute sulphuric acid. Now heat and add, drop by drop, 



