Remarks on Formic Acid. 143 
latter are made to boil previous to the addition of the acid; but so 
perfect is the reduction and precipitation when a formate of 
or soda is employed instead of the uncombined acid, that Débereiner 
‘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.t — 
‘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- 
bi ether the oxide be a per or prot-oxide, the principle i 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 zie upon. If the reduction of the per-oxide be 
the formic acid will be resolved into water and carbonic 
* Annales de Chim. Jan. 1833. + Journal de Pharm. Tome x1x. p. 485, 
