CD4.2 What factors affect the drying potential of an oil? Aims:  To use information from experiments to decide what factors affect the drying potential of an oil.  To make some deductions about the complex chemistry of the drying process.

Different types of oil: If a drying oil is exposed to air, it eventually becomes a rubbery solid. If only a thin layer is exposed, it becomes hard. ~ linseed Non-drying oils do not harden in this way, but they may thicken on heating. ~ olive In between the two extremes are the semi- drying oils. These thicken and form a skin when exposed to air at high temperatures. ~ sesame

Iodine numbers. Natural oils can be classified according to their iodine number. This is calculated on the basis of how much iodine(I) chloride (ICl) will react with the oil. The more ICl reacts with the oil, the higher the iodine number. How is the drying potential of an oil related to its iodine number?

Ignore the triester, consider the carboxylic (fatty) acids

Curve a is for a film of linseed oil prepared and dried in the dark, and weighed under red light. Curve b is for an identical film of linseed oil prepared, dried and weighed in diffuse daylight. Figure 2: The drying of linseed oil. No significant increase in mass was observed if the linseed oil samples were kept in an atmosphere of nitrogen.