Perchloric acid is water soluble and has a specific gravity of 1.77,which means it is heavier than water. However, it is water soluble and will mix rather than form layers. Upon contact with water, heat is produced. Boiling point is 66F and vapor density is 3.46, which is heavier than air. Perchloric acid is incompatible with acetic anhydride, bismuth and its alloys, alcohols, paper, wood, and other organic materials. The four-digit UN identification number for concentrations greater than 50% is 1873. Concentrations less than 50% have a four-digit identification number of 1802. The NFPA 704 designation is health 3, flammability 0, and reactivity 3. There is an “oxy” prefix in the white section of the 704 diamond, indicating an oxidizer