52 M. Berthelot on the Decomposition of Hydrobromic Acid. 



On this relation Berthelot founds a new method for the forma- 

 tion of formic acid, which consists in placing carbonic oxide under 

 conditions favourable to the fixation of the elements of water. 

 By enclosing carbonic oxide along with moist potash in a flask, 

 and heating for several days, this condition is satisfied : the car- 

 bonic oxide is perfectly absorbed by the potash, which is con- 

 verted into formiate of potash, from which formic acid is obtained 

 by appropriate methods. 



In the hope of uniting directly nascent carbonic oxide with 

 the elements of water, Berthelot investigated the decomposition 

 of oxalic acid at 100° C. under different circumstances; heated 

 alone, it is, to a slight extent, decomposed into carbonic acid 

 and carbonic oxide. This decomposition is much accelerated by 

 the presence of acids, and is not due to a chemical but to a cata- 

 lytic action. AVhen oxalic acid is heated to 100° C. with syrupy 

 glycerine, a copious evolution of pure carbonic acid takes place. 

 At the expiration of some time this evolution ceases, and the 

 glycerine then contains half the carbon of the oxalic acid 

 in the form of formic acid, which is not in combination with the 

 glycerine, but merely dissolved like ammoniacal gas in water. 



Here the carbonic oxide and the water produced simulta- 

 neously and in the nascent state from the decomposition of the 

 oxalic acid unite to produce formic acid, the glycerine exercising 

 merely a catalytic action. 



By repeatedly adding water to the glycerine and distilling, the 

 whole of the formic acid contained in it passes over. This pro- 

 cess is extremely productive, as nearly the theoretical quantity is 

 obtained, and the glycerine may be used over and over again, for 

 it is not acted on. 



By this means also pure carbonic oxide may be obtained ; for 

 if in the preparation of formic acid, after the evolution of car- 

 bonic acid has ceased, the glycerine be heated to 200°, the whole 

 of the formic acid contained in it is decomposed into water and 

 carbonic oxide, which passes off perfectly pure. 



When carbonic oxide is passed into a saturated solution of 

 protochloride of copper in hydrochloric acid, a compound of the 

 two bodies is obtained which crystallizes in pearly laminje, and 

 Las the formula 



4Cu2 CI, SCO 7H0. 



Berthelot found that hydrobromic acid, when left in contact 

 with mercury for a very long time, is decomposed into bromide 

 of mercury and hydrogen. The same change takes place, but 

 much more rapidly, when these bodies are heated together to 

 100° C. This slow decomposition of hydrobromic acid by mer- 

 cury is a new example of the influence of time on chemical action. 



