Braconnot on a Green Colour. 309 



with a little water, than when we employ their solutions, which 

 is undoubtedly owing to the insolubility of the hydroxanthic 

 acid in water. Black oxide of copper, yellow oxide of lead, 

 red oxide of mercury, each, when introduced into the hydroxan- 

 thic acid, under water, are quickly converted into xanthides, 

 which nowise differ from those procured by precipitation. With 

 oxide of mercury the action is very lively. 



Hydroxanthic acid takes fire in the air instantly, on tlie 

 approach of a burning body, occasioning a strong odour of 

 sulphurous acid. When exposed to heat, in a suitable vessel, 

 it is decomposed at a temperature much below that of boiling 

 water; and there appear to be formed carburet of sulphur, and 

 an inflammable gas. No odour of onions, or of sulphurous acid, 

 is manifested. 



Iodine was employed for ascertaining whether this new acid 

 contained hydrogen, and the results show that it does. When 

 iodine is introduced into newly-prepared hydroxanthic acid, 

 covered with water, there is manifested instantly a lively 

 action ; the iodine is set in motion on the surface of the acid, 

 and is dissolved. The acid becomes in part opaque, and is 

 coloured at first yellow, then brown, — so that we have soon at 

 the bottom of the vessel an oleaginous liquid of a red-brown ; 

 but, after a little time, the colour begins to disappear, and, in 

 the space of some minutes,) provided too much iodine has not 

 been added,) there results a liquid, oily, opaque, and faintly 

 yellow. The watery liquor, which floats over the oleaginous 

 liquid, is almost colourless ; it is more or less milky, — but, by 

 means of a filter, we obtain it perfectly limpid. When tried by 

 the proper tests, this liquor is found to be a solution of hydriodic 

 acid. The oleaginous liquid which remains, when we have 

 treated hydroxanthic acid with a sufficient quantity of iodine, 

 no longer yields xanthide of copper, with a sulphate of this 

 metal. Comparative trials were made with carburet of sulphur, 

 iodine, and water; the iodine combines with the carburet, 

 colouring it violet; but, as might be presumed, no trace of 

 hydriodic acid is produced. — Ann. de Chi?n. et de Phys., xxi. 160. 



7. On a very beautiful Green Colour. By M. Henri 

 Braconnot. 



M. Noel, who has a fine manufacture of painted paper at 

 Nancy, sent M. Braconnot a superb green colour, known in com- 

 merce for some years, in order that he might analyze it. A ma- 

 nufacturer of colours at Schweinfurt was said to possess the sole 

 secret of its preparation, Of all the methods tried by M. Bra- 

 connot to obtain this colour, the following succeeded best: — He 

 dissolved six parts of sulphate of copper m a small quantity of 

 hot water ; and, on the other hand, he boiled in water six parts 

 of arsenious acid, witli eight parts of the potash of commerce, 



