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IX. Intelligence and Miscellaneous Articles. 



DISTINCTIVK CHARACTERS OF TANNIN AND GALLIC ACID. 



TO determine the different properties of these substances, M. 

 Pfaff employed them of the greatest purity, and he obtained the 

 following results. In a dilute solution of gold, gallic acid gives a 

 blue greenish colour, which appears brown by reflected light, and the 

 gold is perfectly reduced. Tannin merely reduces the gold to a lower 

 state of oxidation, and the liquor becomes purple. Gallic acid a 

 faint yellowish tint in the solutions of titanium. Tannin precipitates 

 orange-red flocculi. Tannin precipitates tartarized antimony white, 

 but gallic acid occasions only slight turbidness after a considerable 

 time. Gallic acid renders the caustic alkalies brown ; the colour 

 which it produces with the carbonated alkalies is at first yellow, 

 with a brownish tint, but it becomes soon of a deep green. Tannin 

 is precipitated by the pure and carbonated alkalies, and the liquor 

 becomes brown, without changing to green. The salts of mor- 

 phia, strychnia, quina and cinchonia, are not precipitated by 

 gallic acid, but they are by tannin. In its combination with the 

 alkalies, tannin seems to undergo a change, which approximates it 

 to gallic acid. The scum of coflee owes its property of turning the 

 white of eg^ green, with the influence of the air, to the gallic acid 

 M'hich it contains ; and the white of eg^^ appears to produce this 

 effect by the carbonate of soda which enters into its composition. 

 M. Pfaff' did not find any gallic acid in the plants which contain 

 emetin and veratria. — Scliweis^gcr's Annals, Journal de Pharmacie, 

 Aug. 1829. "" 



PRECIPITATE OF SILVER RESEMBLING THE PURPLE POWDER 

 OF CASSIUS. 



M. Frick states that if a dilute solution of tin in nitric acid, pre- 

 pared 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 does not possess the jjroperty of colouring glass. — Ibid. 



ON SOME PROPERTIES OF SILVER: BY M. WESLAR. 

 This author states, that chloride of silver which is coloured by 

 light, is not, as has been generally admitted, a mixture of reduced 

 silver and undecomposed chloride, but a new compound containing 

 less chlorine than the common chloride of silver, M. Weslar calls it 

 subchloride : one circumstance, among others, favourable to this 

 opinion is, that the chloride of silver coloured by light is not acted 

 upon by nitric acid. Ammonia and a solution of muriate of soda 

 convert this subchloride into metallic silver and chloride. Subchlo- 

 ride of silver cannot be obtained free from chloride by exposing the 

 latter to light ; it may be procured by allowing silver to remain in 

 a solution of muriate of copper or iron. It is owing to the produc- 

 tion 



