208 
DR. GLADSTONE ON CIRCUMSTANCES MODIFYING 
The converse of this experiment was also tried. The molybdous oxide dissolved in 
hydrochloric acid of a green colour. The addition of hydrofluoric acid to this gave 
at the first moment a rich purple, which was immediately succeeded by a white pre- 
cipitate, insoluble in any excess of hydrofluoric acid, but readily soluble in hydro- 
chloric acid with the reproduction of the green. 
Manganese salts. 
Intermediate between the protoxide of manganese and the non-basic oxides, there 
exists a brownish-red salifiable compound, of the formula Mog O 4 . It is described in 
Gmelin’s Handbook under the designation “ manganoso-manganic oxide.” Its solu- 
tion in hot phosphoric acid or cold oil of vitriol is red, but it dissolves in other acids 
with a deep brown colour. 
I prepared the sulphate and hydrochlorate of this base, and found that the addition 
of hydrochloric acid in excess caused a change in the colour of the sulphate from red 
to reddish brown, and eventually brown ; while, on the other hand, the addition of 
sulphuric or phosphoric acid in excess to a solution of the brown chloride converted 
it into the red salt. Thus it appears that the oxide in question has no such affinity 
for either one of these acids, but that it is displaced more or less by the other. 
Blue Gallate of Iron. 
Gallic acid, when added to iron salts, is apt to strike a deep blue colour, from the 
formation of a very stable compound of the organic acid with both the basic oxides 
of iron at once. 
A portion of this compound was produced by allowing gallic acid to stand for 
eighteen hours with the hydrated sesquioxide. The effect of successive portions of 
a strong solution of sulphate of soda was tried. 
Sulphate of ^ater added to 
soda added. comparative 
solution. 
Sulphate of Water added to 
sodLdded. comparative 
solution. . 
5 measures=10 measures. 
15 measures=24 measures. 
26 measures=36 measures. 
35 measures =46 measures. 
Another blue solution was prepared by mixing solutions of gallic acid and of green 
vitriol that had been exposed to the air. The effect of sulphuric acid was tried. 
Sulphuric acid Water added 
added comparative 
solution. 
Sulphuric acid Water added 
added. comparative 
solution. 
1 measure = 9 measures. 
2 measures=18 measures. 
4 measures = 34 measures. 
6 measures=46 measures. 
8 measures=55 measures. 
10 measures = 63 measures. 
14 measures=105 measures. 
16 measures =136 measures. 
18 measures=174 measures. 
20 measures =204 measures. 
These numbers give the singular curve in Plate IX. fig. 7* The mixture is of far 
