The solubility of a known amount of germanium sesquioxide is conducted in a known amount of boiling distilled water.  GeO₂ is not readily soluble in boiling water and is much more soluble in acid.  Dangerous levels of GeO₂ will produce a cloudy solution or insoluble material in the bottom of a flask.Germanium lactate citrate is a highly soluble combination of germanium dioxide, lactic and citric acid.  The solubility test will not flag the presence of germanium dioxide in this instance but other analytical tests will readily detect it.