146 Remarks on Formic Acid. 



ii'othing 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 tlie 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 loater. 



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, Sec. 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 of carbon separates at the same time. Sugar, for example, 

 gave a large deposit of a snuff brown color, and resembling in its properties, the 

 v2min of rotten wood. 



