SYNTHESIS OF FORMIC ACID. 85 



Carbonic acid Water Carb-anhydride 



CH a 3 - H,0 = CO, 



which is reconvertible into the acid or a salt thereof by actual 

 or potential rehydration, thus : 



Carb-anhyd. Lime Chalk 



CO, + Ca"0 = CCa"0 3 



Carb-anhyd. Potash Potas. bicarb. 



CO, + KHO = CKH0 3 



The deoxidised forms of carbonic acid and anhydride, respec- 

 tively, or formic acid CH 2 2 , and carbonic oxide CO, are readily 

 procurable therefrom by processes of reduction, and are correlated 

 with each other in a similar manner. For example, by the de- 

 hydration of formic acid, we obtain carbonic oxide, 



Formic acid Water Carb. oxide 



CH 3 0, - H,0 = CO; 



convertible into a formiate by means of caustic alkali, thus : 



Carb. oxide Potash Potas. formiate 



CO + KHO = CKHO, 



(89.) The production of formic acid or formiates by the 

 reduction of carbonic acid with sodium (Kolbe), and by the 

 combination of potash with carbonic oxide (Berthelot), being 

 among the early examples of the formation of organic from in- 

 organic compounds, excited on their first announcement a large 

 amount of chemical interest. Formic acid, indeed, is a substance 

 enjoying a very extensive natural distribution. In the vegetable 

 kingdom it occurs in the juice of the stinging nettle, in decaying 

 pine needles, and as a product of the spontaneous oxidation of 

 turpentine. In the animal kingdom it has been occasionally re- 

 cognised in human blood, urine, perspiration, and in the fluids of 

 the spleen and muscles. It also exists largely in the juice of red 

 ants, from which it may be obtained by simple distillation, and 



