Remarks on Formic Acid. 143 



latter are made to boll previous to the addition of the acid ; but so 

 perfect is the reduction and precipitation when d. formate of potassa 

 or soda is employed instead of the uncombined acid, that Dobereiner 

 and others have strongly recommended the process, when chemists 

 are desirous of separating the precious metals from the common or 

 more easily oxidizable ones.* M. Gobel has also shown, that by 

 simply combining the oxides with formic acid, and heating the dry 

 salts thus obtained over a spirit lamp, it is easy to procure, in a state 

 of perfect reduction, the metals zinc, copper, cadmium, bismuth, 

 lead, nickel, uranium, cerium, and cobalt. '\ 



The mode of action is obvious, and the facility of reduction equally 

 intelligible. The oxide of carbon, composing the formic acid, re- 

 moves oxygen from the metal and becomes carbonic acid, generally 

 leaving the reduced matter surrounded by the excess of the former 

 gas. Carbonic oxide, even when completely gaseous, combines 

 freely with oxygen at a dull red heat, as was shown by Davy, and 

 therefore, in the above examples, where these substances have the 

 additional advantage of previous condensation to the solid state, the 

 formic acid must be very superior to hydrogen when the tempera- 

 ture does not much exceed obscure redness. It is, in fact, together 

 with carburetted hydrogen, the great reducing agent in all furnace 

 operations ; for the carbon of the fuel, while in its solid state, must 

 be nearly Inoperative at all times, and the carbonic acid which ap- 

 pears so abundantly in all such cases, if the reduction of the ore 

 be complete, should never acquire more than one half of its oxy- 

 gen from the air which enters the furnace. Formic acid, it is obvi- 

 ous, will enable the chemist not only to recover the metal, but to 

 determine accurately the quantity of oxygen with which it was com- 

 bined — whether the oxide be a per or prot-o-sXAe, the principle is the 

 same — a given weight of it is to be boiled with formic acid in excess. 

 The latter being always decomposed by the operation, furnishes 

 carbonic acid, every atom of which contains an atom of oxygen 

 obtained from the metal ; and by the same data, when the oxide 

 is in excess, the whole of the formic acid being decomposed into a 

 mixture of carbonic oxide and acid, we have only to collect, sepa- 

 rate and determine the amount of each of these gases, in order to 

 arrive at a knowledge of the quantity of formic acid that existed in 

 the solution operated upon. If the reduction of the pe7--ox\de be 

 complete, the formic acid will be resolved into water and carbonic 



* Annales de Chim. Jan. 1833. t Journal de Pharm. Tome xix. p, 485. 



