128 Chemistry and Chemical Arts. 
ebullition. ‘The acid is gradually volatilized without separating the 
least trace of the metal; nevertheless the formate of soda effects 
the entire precipitation of these metals, partly in brilliant scales, and 
partly in a pulverulent state. ‘The solutions of nitrate of silver and 
of mercury are decomposed by free formic acid, but the decomposi- 
tion is more prompt by the alkaline formates. 
The red oxide of mercury offers a sure and easy method of deter- 
mining the quantity of free formic acid, or when it is mixed with 
other acids, or combined with bases. The proportion of formic acid 
is determined by the volume of carbonic acid disengaged, when a 
liquid containing the formic acid is heated with the red oxide of 
mercury, the carbonic acid bemg collected and measured in a con- 
venient apparatus. When the formic acid is combined with bases, 
it is necessary to add beside the red oxide of mercury, some acetic 
acid, in order to set the formic acid at liberty. 
The formates of zinc, of copper, of cadmium, of bismuth, of lead, 
of nickel, of uranium, of cerium, and of cobalt, exposed toa red heat 
in a glass tube held in the flame of an alcoholic lamp, are decompo- 
sed, and their oxides completely reduced. ‘The use of formic acid 
in obtaining the rare metals is so great, that it merits the preference 
over hydrogen ; and since the production of this acid is now attend- 
ed with so little expense, it is to be hoped that we may be able to 
effect the reduction of the noble metals on a larger scale than here- 
tofore. 
The formic acid may moreover, be employed in order to ascertam 
the quantity of oxygen contained in the peroxides. For this pur- 
pose, a determinate quantity of the peroxide is heated with the for- 
mic acid ; the gas disengaged during the operation, and which is a 
mixture of carbonic acid and of the air of the vessels, is collected ; 
the use of potassa enables us to determine the volume of carbonic 
acid present in the mixture, paying regard to the atmospheric pres- 
sure, its temperature and state of humidity ; the volume of this acid 
is divided by 2; the quotient expresses the volume of oxygen de- 
rived from the peroxide. 
The process of Douseriner for obtaining the formic acid does 
not afford it perfectly free from acetic acid., GoBeL recommends to 
get rid of this, by employing instead of chalk, carbonate of lead 
with the aid of heat; the acid liquor passes over by distillation and 
separating by crystallization, from the acetate which dissolves easily. 
