Cobalt chloride is an inorganic compound that changes color in response to humidity and is one of the most commonly used cobalt compounds in lab applications. The International Agency for Research on Center (IARC) has placed this compound in Group 2B, stating that it is possibility carcinogenic to humans and toxic to aquatic organisms. It is also potentially harmful to the environment.
As an indicator of moisture levels, its most common usage is as a dessicant gel called Blue Indicating Silica Gel that turns from blue to pink when moisture is present. Humidity indicator cards that work on the same principle, with dots changing from blue to pink, also use this substance.
This compound may also be found in science experiments, color changing novelties, as an ingredient in invisible ink, as a binding agent to harden metals and as a starting point for the synthesis of cobalt compounds in labs.