76 FORMIC ACID. 



1. Formic Acid. 

 CH 2 2 = H.CO.OH. 



Occurrence. In ants, in common nettles, in pine 

 needles. 



Formation, (a) From carbonic oxide; potassium 

 hydroxide unites with it when heated for some time 

 at 100, forming potassium formate ; (b) from carbonic 

 anhydride ; potassium spread out on a basin under a 

 bell-jar inserted in lukewarm water and kept constantly 

 filled with carbonic anhydride is converted into a mix- 

 ture of potassium formate and bicarbonate ; it, in fact, 

 always results in small quantities whenever hydrogen 

 in statu nascendi and carbonic anhydride in a state of 

 transmission come together, as, for instance, by the 

 action of sodium-amalgam on a concentrated solution 

 of ammonium carbonate, by the, addition of a mixture 

 of zinc and zinc carbonate to hot caustic potassa ; (c) 

 from methyl alcohol by means of oxidation ; (d) from 

 prussic acid by treating with alkalies or dilute acids ; 

 (e) from oxalic acid, by heating, or by the action of 

 sunlight upon an aqueous solution of the acid contain- 

 ing a salt of uranium ; (/) from chloroform, iodoform, 

 and bromoform by treatment with alcoholic potassa ; 

 (g) from a large number of organic substances, starch, 

 sugar, tartaric acid, etc., by distillation with dilute sul- 

 phuric acid and black oxide of manganese or potassium 

 chromate. 



Preparation. By distilling ants with water. Most 

 practicably by treating crystallized oxalic acid with 

 glycerin, from which the water has been separated as 

 thoroughly as possible. The reaction commences at 70 

 and is in full progress at 90. Carbonic anhydride 

 escapes, and a very dilute formic acid distils over. When 

 the evolution of carbonic anhydride begins to grow 

 less active, a fresh quantity of oxalic acid is added and 

 heat again applied. A more concentrated acid now 

 goes over, and, by continued addition of oxalic acid, an 

 acid containing 56 per cent, is finally obtained. For 

 the purpose of obtaining the acid in an anhydrous con- 

 dition, the lead or copper salt is prepared, dried, and 



