PLTL-123 Blue Soap Test
In the manufacturing of some ester types, there may be some of the acid precursors remaining in the product. These acid residues are typically neutralized and washed out of the product. To test if they are adequately removed, a 40 gram sample of ester is dissolved in acetone and Bromo-P-Blue indicator. If yellow, the ester is residue free. If blue, the ester contains the ‘soap’ of the acid precursor. Titration with HCl will give the weight percent (as NaOH) of soap in the product.