Dr. Mahla on Gallic and Galihumic Acid. 383 
origin in sediments of magnesian carbonate formed oy the evap- 
i hese solu- 
Arr. XLI—On Gallic and Gallhumic (Metagallic) acid; by Dr. 
F, Maw, Ph.D., Chicago. 
It is mentioned among the reactions of gallic acid in almost 
every handbook of chemistry, that its solution produces a deep 
bluish-black color with a solution of the salts of the sesquioxyd 
of iron, which disappears, when the solution is heated. <As I 
ave nowhere found an explanation of this fact, I have tried to 
investigate it by some experiments. : ioe 
When the solutions of the sesquioxyd of iron and gallic acid 
are used in a diluted state, the resulting mixture appears only 
slightly colored, but if they are concentrated, it assumes after 
being heated to ebullition, a dark brown tint, and then causes 
black spots on the skin, which can be washed away only with 
the greatest difficulty. Such a solution might perhaps be used 
vantageously as a hair dye. 3 : 
If the iron-solution was not added in too large proportion, 
liquid ammonia no longer precipitates hydrated sesquioxyd of 
iron, but the proto-sesquioxyd (black oxyd). A reduction 
place therefore, the oxygen transforming some of the carbon of 
the gallic acid into carbonic acid, which is freely evolved during 
the ebullition. 
soda was added in 2 —— 
and the black precipitate separated by filtration. A portion 
the filtered dark ‘Siow liquor, after being exactly saturated with 
hydrochloric acid, deposited a voluminous black precipitate, 
which if dried, formed a black shining mass but when freshly 
