148 Remarks on Formic Acid. 



with 4 atoms of carbon deposited, and 2 atoms of hydrogen unac- 

 counted for. 



During the preparation of formic acid by Dobereiner's process, 

 as well as by my own, in which no peroxide of manganese is em- 

 ployed, there is always formed, previous to the carbonization, a con- 

 siderable quantity of volatile oil, which, at first, might be considered 

 as arising from the excess of hydrogen and carbon in the process ; 

 but a special inquiry has convinced me that this is not the case, al- 

 though the oil is so abundant that it may actually be observed floating 

 in drops down the neck of the retort. When the sulphuric acid is 

 so far diluted as not to carbonize the mixture at the heat of boiling 

 water, little else than this spicy oil passes over by distillation ; but as 

 soon as the matter becomes black, its formation ceases, and if we 

 begin at once with sulphuric acid about one half diluted, it does not 

 appear at all ; but, instead of it, strong formic acid, without any for- 

 eign odor, and quite colorless. This volatile oil would not be regard- 

 ed as objectionable by many, since it imparts an aroma to the acid 

 like that of cassia or cinnamon, and a taste somewhat similar to that 

 produced by hydrocyanic acid. 



The process which I recommend, as having been found the most 

 convenient and perfect, for obtaining strong formic acid, is the fol- 

 lowing. 



Mix together in a glass tubulated retort, equal measures of ivaler, 

 oil of vitriol, and clean, but unground rye, (or cracked maiz) — let 

 them be heated to the boiling point, and, as soon as the mass has 

 become thoroughly blackened, add another measure of water and 

 distill off one measure of formic acid. 



By the addition of a further quantity of water, and by fresh dis- 

 tillation, a weaker acid may be obtained, which will answer very well 

 to be added in subsequent operations. Besides being too weak, the 

 product of this second distillation will often contain some sulphurous 

 acid, which seldom appears in the first, and never is essential to the 

 process. It occurs in company with oxide or carbonic acid, and may 

 be removed by agitating, for a short time, the cold formic acid with 

 peroxide of lead, as recommended by Berzelius. 



By employing the whole grain, when small enough, as of rye, wheat, 

 oats, he. and in the great proportion here recommended, the contents 

 of the retort become too solid to froth up easily, so that the medium 

 sized vessels may be employed. Indeed, still smaller ones may be 

 substituted, by simply allowing water to enter through a dropping fun- 

 nel at the tubulure, in proportion as it is removed by the distillation. 



