244 - 7 WV- Davy’s Experiments and Observations 
it continued to give, even to the last portions, a pale yellow 
tinge. 
Magnesia was boiled in one portion of the infusion for a few 
hours ; and mixed in excess with another portion, which was 
suffered to remain cold. In both cases, a deep green fluid was 
obtained, which precipitated the salts of iron, but not the solu- 
tions of gelatine; and the magnesia had acquired a grayish- 
green tint. Water poured upon it became green, and acquired 
the properties of the fluid at first obtained. After long washing, 
the colour of the magnesia changed to dirty yellow ; and the 
last portions of water made to act upon it were pale yellow, and 
altered very little the solutions of iron. 
When the magnesia was dissolved in muriatic acid, a brownish 
and turbid fluid" was obtained, which precipitated gelatine and 
the oxygenated salts of iron. So that there is every reason to 
believe, that the earth, in acting on the astringent infusion, had 
formed two combinations; one containing chiefly gallic acid, 
which was easily soluble in water; the other containing chiefly 
tannin, which was very difficultly soluble. 
Alumine boiled with the infusion became yellowish-gray, and 
gave a clear white fluid, which produced only a tinge of light 
purple in the solutions of iron. When the earth* was employed 
in very small quantity, however, it formed an insoluble com- 
pound only with the tannin and the extract; and the residual liquor 
was found to contain a gallate of alumine with excess of acid. 
The oxides of tin and of zinc, obtained by nitric acid, were 
boiled with separate portions of the infusion for two hours. In 
both cases, a clear fluid, which appeared to be pure water, was 
* Mr. Fiedler, I believe, first observed the action of alumine upon tannin. Van* 
Mg ns’s Journal, Vol. I. page 86. 
