MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
The cobalt chloride test for water. The blue cobalt chloride test paper is held over a test tube of water. The humidity (water vapour) turns the paper from blue to pink. It is important that the paper is stored in low humidity before the test since exposure to 55% relative humidity or greater is sufficient to cause a slow colour change.
Model release not required. Property release not required.