Intelligence and Miscellaneous Articles. 401 



in the process, we shall have (4C+4- + 4H), from which subtract 

 H, or one atom of water, (removed by the sulphuric acid,) and we 

 shall have 4C + 30 + 3H, which is equivalent to one atom of for- 

 mic acid (2 C + 3 0-j-H) together with 2 carbon, precipitated, and 

 2 hydrogen, unaccounted for. Again, assuming (6 C + 5 0-\-5 H) 

 as the formula for one atom of starch, and subtracting 2 H, or two 

 atoms of water, removed by the sulphuric acid, the remainder will 

 be equivalent to one atom of formic acid, (2 C-f-3 O-fH) together 

 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 float- 

 ing 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 boil- 

 ing 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 

 foreign odour, and quite colourless. This volatile oil would not be 

 regarded 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 water, 

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

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

 become thoroughly blackened, add another measure of water and 

 distil 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 

 he 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, &c., 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 funnel at the tubulure, in proportion as it is removed by 

 the distillation. — Sillimans Journal, vol. xxxii. p. 145. 

 Third Series. Vol. 11. No. 68. Oct. 1837. 3 F 



