Formaldehyde also known as methanal is a colorless gas CH₂O relative density 0.815 (at -20°C), melting point -92°C, and boiling point -21°C. It is the simplest aldehyde made by the catalytic oxidation of methanol (500°C; silver catalyst) by air. It forms two polymers: methanal trimmer and polymethanal. The colorless solution of methanal in water with methanol as stabilizer is called formalin, relative density 1.075 – 1.085 which is slightly heavier than water of equal volume and will sink to the bottom in water solutions. When kept at temperature below 25°C a white polymer of methanal separates out. It is used as a disinfectant and preservative for biological specimens. Hypothetically, if formalin can be electrolyzed then the double positive molecular ions CH₂⁺⁺ can be dissolved in an acid solution. These solutions can be used to treat RNA viral diseases such as HIV causing AIDS.