146 Remarks on Formic Acid. 
frothing of this mixture, and which is exceedingly great, it is directed 
to add only half the amount of dilute acid at first, and to make use 
of a retort having five or six times the bulk of the matter to be put 
into it. 
The explanation given by Dobereiner, and other chemists, assigns 
to the peroxide of manganese an agency absolutely necessary for 
success, viz. that, while it parts with a portion of its own oxygen and 
combines, as the protoxide, with sulphuric acid, it is enabled by the 
oxygen thus detached, to convert the tartaric acid (or sugar) into 
formic and carbonic acids. 
The whole of this explanation is, however, incorrect, as will ap- 
pear from the following results of my inquiry. 
1..The presence of peroxide of manganese, (or any other per- 
oxide,) is not only unnecessary, but positively injurious and produc- 
tive of much inconvenience. It is positively injurious in consequence 
of the power which all peroxides have of decomposing formic acid, 
and productive of inconvenience in consequence of the vast amount 
of carbonic acid which it produces with the formic acid and the car- 
bon, deposited during the operation. ‘The latter is, in fact, the cause 
‘of the excessive frothing. | 
2. Sulphuric acid is not essential. The formic acid was prepared 
by phosphoric acid as well as by the chloride of tin; and no doubt all 
other substances, capable of converting alcohol into ether, may be 
shown to possess the same power. In no case does sulphuric acid, 
phosphoric acid, or chloride of tin undergo any decomposition, unless 
incidentally. 
3. The formic acid may be procured from almost every kind of 
vegetable matter that is capable of being promptly blackened by con- 
tact with strong sulphuric acid. It rarely appears previous to the 
carbonization,* and only when the sulphuric acid possesses'a powerful 
affinity for water. 
It would appear, from these particulars, that the process for ob- 
taining formic acid artificially is analogous to those operations. for 
converting cotton, ligneous matter, &c. into gum—gum or starch 
into sugar, and alcohol into ether or olefiant gas, as far as regards 
_ * When the chloride or sulphate of tin is employed, perfect carbonization does 
not take place, yet the formic acid is generated readily. There is no doubt, how- 
ever, that some variety * carbon separates at the sametime. Sugar, for example, 
gavea snuff-brown color, and resembling in its properties, the 
ulmin of rotten een 
