Artificial Formation of Foj'mic Acid. 19? 



merce in water until no more carbonic acid is disengaged. 

 .3d, mix this solution while hot and concentrated, by a little 

 at a time, with the former; continually stirring it until ef- 

 ferveircence ceases. Care must be taken not to add the 

 arsenite of potash in excess. An abundant precipUate is 

 formed of a dirty yellow colour. 4th, add acetic acid, (about 

 three parts) or such a quantity that there may be a slight 

 excess of it sensible, by its odour after the mixture ; by de- 

 grees the precipitate diminishes in volume, and at the end 

 of a few hours there is spontaneously deposited a powder 

 of a slightly crystalline texture and of a very beautiful green. 

 5th, separate the supernatant liquor, (which by remain- 

 ing too long on the colour, might deposit oxide of arsenic, 

 which would render it pale,) and then treat the colored de- 

 posite with a large quantity of boiling water, to remove the 

 last portions of arsenic which are not held in combination. 



It is better (Braconnot observes,) to make use of an ar- 

 senite of potash, well saturated with arsenic. It is true, that 

 part of the arsenious acid remains in the mother waters, 

 but this may serve for the preparation of Scbeele's green, 

 which is commonly employed for paper of an inferior qual- 

 ity. It seems to me that when we added to the mixture a 

 small quantity of this green, it favored the production of the 

 superior color, somewhat in the same manner as a crystal 

 attracts its kindred molecules in a saline solution. 



The colors which we obtained by the proceeding method 

 were judged by several persons to be more lively than that 

 of Schweinfurt. 



29. Artificial formation of Formic Acid. — Dobereiner 

 has discovered that when tartaric acid, or cream of tartar, 

 peroxide of manganese and water, are heated together, a 

 tumultuous action begins, a large quantity of carbonic acid 

 is disengaged, and a liquid acid distils, which, on superficial 

 examination, might be taken for acetic, but which, on a 

 stric er enquiry, proves to be formic acid. 



If to the materials above described, there be added sul- 

 phuric acid, the tartaric acid will be entirely converted into 

 carbonic acid, water, and formic acid, and there will conse- 

 quently be obtained a larger quantity of the latter. The 

 best proportions of the mixture are^ — 



