Chemical Science, " 211 



17. Purple Precipitate of Silver. — M. Frick states, that if a di- 

 lute solution of tin in nitric acid, prepared without heat, be mixed 

 with a dilute solution of nitrate of silver, the solution^ after some 

 minutes, becomes yellow, afterwards brown, and eventually of a 

 deep purple colour : if dilute sulphuric acid be added to it, a deep 

 purple precipitate will be obtained, but which, although it other- 

 wise resemble the purple precipitate of gold, does not possess 

 the property of colouring glass. — Phil. Mag. N. S. vii. 58. 



18. Oil the Action of Alkalies on Organic Bodies. — ^We gave M. 

 Gay Lussac's highly interesting paper on this subject in a former 

 number of our Journal *. On the 16th of November, M. Gay- 

 liussac stated to the Academy of Sciences, that since his first ob- 

 servations on the formation of oxalic acid, he had also ascertained, 

 that acetic acid and water were very generally produced when the 

 caustic alkali was made to act either upon animal or vegetable 

 substances, in the manner before described. 



19. Preparation of Formic Acid. — Dobereiner's process for pre- 

 paring this curious acid has been given in a former volume of this 

 Journal f. M. Wohler recommends the following process for the 

 same purpose : — A mixture of starch and peroxide of manganese 

 is to be put into a retort, sulphuric acid poured upon it, and 

 the whole subjected to distillation j much carbonic acid gas is 

 evolved, and an acid liquor passes over at the same time, which has 

 a very penetrating smell, and strongly irritates the eyes : this is 

 formic acid, rendered impure by a volatile matter, to which its 

 strong odour is to be attributed. When the liquor is saturated 

 with an oxide the smell ceases, and the solution has a yellow tint. 

 It is only necessary to distil the formiate thus obtained with sulphu- 

 ric acid to obtain pure formic acid without any smell but that which 

 it naturally has. The salts which even the impure acid forms 

 with baryta, lime, and lead, have precisely the same crystalline 

 form as the same salts prepared with the nitric acid. The salt of 

 lead was analysed : its acid was found to contain the same consti- 

 tuents as common formic acid. — Henstnann's Repertoire — Phil. 

 Mag. N. S. vii. 60. 



"O" 



20. Pelletier on a new Vegeto-alkali. — M. Pelletier, in a letter 

 to M. Gay-Lussac, remarks, that a particular bark is resorted to 

 in Peru for the purpose of mixing with the bark of cinchona 

 (quinquina cassaya), as an adulteration. The bark has no me- 

 dical properties j has not yet been botanically distinguished j is 

 still under chemical investigation, but has been found to contain 

 a new vegeto-alkali. It may be distinguished from tonic bark 

 (quinquina cassaya) by a drop of nitric acid, which renders the 

 former of a deep green, and the latter of a red-brown. 



♦ See vol. vi, p. 414. f Quarterly Journal of Science, xiv. 232. 



