Naphthalene Crystals
Although it all comes down to some relatively ‘simple’ science I am totally fascinated by the naphthalene crystals which have formed in our bird skin drawers.
Mothballs have historically been used as a pest deterrent within natural history collections, particularly with bird skins. The mothballs are placed in closed containers where the naphthalene can sublimate and the gas displaces oxygen. This vapour is toxic to museum pests particularly clothes moth like Tineola bisselliella.
The crystals are formed by processes called sublimation and deposition. These processes are very much like vaporization and condensation. Sublimation is the process of transition of a substance from the solid to gas phase without the intermediate liquid phase being observed, while deposition is the reverse where the gas phase condenses and reforms into a solid phase without a liquid phase being observed.
In open environments, during the gas phase, the particles will drift away from the solid and the mothballs will eventually sublime completely away. However, in closed environments, like our drawers, the gas particles cannot escape and the concentration of the gas will increase causing the rate of deposition to climb. During the deposition process the gas particles collide with one another and condense forming crystals of naphthalene, C10H8.
The naphthalene particles diffuse rapidly into the air and its smell can be felt several meters away. Within natural history collections the distinctive smell of bird stores is a consequence of naphthalene sublimation.
Naphthalene is a volatile organic compound (VOC) and an aromatic hydrocarbon, this being so it is classed as a non-polar molecular substance. Where the naphthalene crystals have formed on and around feathers it can be solubilised using non-polar solvents (like dissolves like) such as white spirit or solvents with non-polar characteristics like acetone.
Mothballs have historically been used as a pest deterrent within natural history collections, particularly with bird skins. The mothballs are placed in closed containers where the naphthalene can sublimate and the gas displaces oxygen. This vapour is toxic to museum pests particularly clothes moth like Tineola bisselliella.
The crystals are formed by processes called sublimation and deposition. These processes are very much like vaporization and condensation. Sublimation is the process of transition of a substance from the solid to gas phase without the intermediate liquid phase being observed, while deposition is the reverse where the gas phase condenses and reforms into a solid phase without a liquid phase being observed.
In open environments, during the gas phase, the particles will drift away from the solid and the mothballs will eventually sublime completely away. However, in closed environments, like our drawers, the gas particles cannot escape and the concentration of the gas will increase causing the rate of deposition to climb. During the deposition process the gas particles collide with one another and condense forming crystals of naphthalene, C10H8.
The naphthalene particles diffuse rapidly into the air and its smell can be felt several meters away. Within natural history collections the distinctive smell of bird stores is a consequence of naphthalene sublimation.
Naphthalene is a volatile organic compound (VOC) and an aromatic hydrocarbon, this being so it is classed as a non-polar molecular substance. Where the naphthalene crystals have formed on and around feathers it can be solubilised using non-polar solvents (like dissolves like) such as white spirit or solvents with non-polar characteristics like acetone.