Violet tungsten oxide solubleness refers to soluble extent in different solvent, it is insoluble in water, acid, ethanol, but soluble in alkali solution to have chemical reaction.
Solubleness means the soluble extent of one material, the material which will dissolve is called solvend, the material which will let other substance dissolve is called solvent, the generated mixed liquor is called solution.
Solvent is a kind of liquid which can solving solid, liquid or gas solvend. Water is the most common seen solvent in our daily life. Solvent should not react with solvend which should be of low activity. Alkali solution is not solvent of violet tungsten oxide, so they will reacts with each other.