Drying oils iodine number

Complete analysis of a varnish is often extremely difficult. The difficulties are greatest with oil varnishes, these containing drying oils and resins which have been heated so that their physical and chemical characters (solubility in different solvents, density, colour reactions, iodine, acid and saponification numbers, etc.) are changed. Even with simpler varnishes it is difficult to ascertain if they are prepared from a single resin or from several. Minor difficulties are encountered in the determination of the nature of the volatile solvents, although these are sometimes complex mixtures. 

Addition of (SCN)2 to unsaturated acids has a place in the analysis of fats and drying oils. Whereas iodine adds to all C=C bonds, (SCN)2 is only partially added. From the differences between iodine numbers and thiocyanate numbers (see page 114) conclusions can be drawn about, e.g., the composition of fatty acid mixtures containing oleic, linoleic, and linolenic acid. For details of the technique see Kaufmann.785... 

Stillingia oil n. Pale yellow, limpid, drying oil peculiar odor mustard-like taste. Slightly soluble in alcohol. Sp gr, 0.943-0.945 iodine number, 160 saponification value, 210. 

Thus, the iodine number is a measure of the degree of unsaturation of the oil and an indication of its drying rate. 

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