154 COMBUSTIBLE ACIDS. 



covery, which has put it in my power to obtain 

 Formation formic acid, and to ascertain its properties. He 



of this acid 



found that, when tartaric acid, or bitartrate of 

 potash, is mixed with black oxide of manganese 

 and water, and a gentle heat applied, an effer- 

 vescence takes place, and carbonic acid gas is 

 evolved, while a colourless acid liquid passes over 

 into the receiver, which is formic acid. When 

 sulphuric acid is added, the whole of the tartaric 

 acid is decomposed, and a greater quantity of 

 formic acid is obtained. During the process, 

 the tritoxide of manganese is converted into 

 protoxide, which combines with the sulphuric 

 acid ; or, if that acid be not present, with the 

 tartaric and formic acids. The best proportions 

 he finds to be 



1 part of crystallized tartaric acid, 



2 J parts tritoxide of manganese, 



2J parts of sulphuric acid, which should be diluted 

 with twice or thrice its weight of water.* 



If we compare the constituents of tartaric and 

 formic acids, we will be enabled to see what 

 takes place in this case. 



HYDROGEN. CARBON. OXYGEN. 



Tartaric acid 2 +4 +4 

 Formic acid 1 +2 +3 



Difference 1 +2 +1 



* Gilbert's Annalen, LXXI, 108. 



