Intelligence and Miscellaneuus Arlicles. 155 



came much darker with persulphate of iron, and of a blueish black 

 colour with the protosulphate of iron; these are characters which, 

 as we shall presently see, indicate the presence of pyrogallic acid, 

 but not that of gallic acid ; the same brown liquor was abundantly 

 precipitated into a glutinous elastic mass by gelatin. It therefore 

 contained a ditierent kind of tanning from that which exists in the 

 gall-nut. It may -be inferred from these results, that heat, by acting 

 on gallic acid, occasions its elements to unite in a new order to give 

 rise to tanning matter and pyrogallic acid. Bouillon-Lagrange has 

 already remarked that the sublimed acid possesses characters which 

 prevent its being confiiunded with common gallic acid. According 

 to Berzelius it does not redden litmus paper; Braconnot always 

 found it to do so. Suspecting that this effect might be derived 

 from the tanning matter which it retains, that was separated by oxide 

 of tin ; it still however reddened litmus paper, but not so strongly 

 as gallic acid. 



The taste of pyrogallic acid is sharp and bitter ; it requires 2\ 

 parts of water at 55° Fahrenheit, for solution, whereas gallic acid 

 requires 100 parts at the same temperature. When sublimed a 

 second time the greater part is decomposed, leaving a residue of 

 tanning matter or of charcoal. Like the gallic acid it is soluble in 

 aether; the aqueous solution is perfectly colourless ; but exposed 

 to the air it becomes gradually coloured and eventually deposits 

 a brown matter which has the properties of ulmin, which increases 

 more and more as the water lost by evaporation is renewed, and in 

 some days the acid is entirely decomposed. 



If a solution of persulphate of iron be poured into one of pyrogallic 

 acid, the latter is instantly decomposed by the oxygen of the per- 

 oxide of iron, which becomes protoxide. The solution becomes of 

 a very dark-brown colour, which by spontaneous evaporation yields 

 a remarkable quantity of colourless transparent crystals, that may 

 be separated from a brown matter by alcohol ; these crystals are 

 protosulphate of iron. The brown spirituous solution contains no 

 more iron : evaporated with a gentle heat it leaves a residue, 

 which re-dissolved in water, yields a very sour astringent solution, 

 containing free sulphuric acid and a tanning matter which precipi- 

 tates gelatin abundantly. 



The protosulphate of iron gives a blackish blue colour to a solu- 

 tion of pyrogallic acid. If into an aqueous solution of the same 

 acid only a very little of the persulphate is put, so as to decompose 

 only a part of the acid, the protosulphate of iron produced gives 

 eventually a blue colour to the solution, 'i'hese reagents act in a 

 very different maimer with gallic acid ; for the persalts of iron al. 

 ways give a fine blue colour with it, while the ))rotosalts occasion 

 no change. 



When nitrate of silver or protonitrate of mercury is added to an 

 aqueous solution of pyrogallic acid, the whole of tiie metal is in 

 .stantly precipitated in the metallic state. 



A saturated solution of pure gallic acid in water is not rendered 



turbid by nitrate of silver; after some time the solution becomes 



X 2 brown, 



