Free glycerol in soap

The determination of free glycerol in soap has been improved and shortened. 1. When it is known that there are no substances which interfere with periodic acid reaction, the directiodimetric method is applicable. However, if the glycerol content is below 1%, the accuracy and precision are only fair. 2. The extraction-iodimetric method is applicable when the sample contains no periodic acid reducing substance other than glycerol or when such substances are soluble in chloroform. 3. The extraction-acidimetric method is preferable when the sample contains periodic acid reducing substances other than glycerol and which are soluble in the aqueous acid solution along with the glycerol.