BS ISO 685-2020 Analysis of soaps – Determination of total alkali content and total fatty matter content

BS ISO 685-2020 Analysis of soaps – Determination of total alkali content and total fatty matter content. 8.3 Determination 8.3.1 General Dissolve the test portion (8.2) in about 100 ml of hot water. Pour the solution into one of the separating funnels (2) or into the extraction cylinder (3) and wash the beaker with small quantities of water, adding the washings to the separating funnel or to the extraction cylinder. Add a few drops of the methyl orange solution (51) and then, from a burette, add, while vigorously shaking the separating funnel or the extraction cylinder, an accurately measured known volume of the sulphuric acid solution (5.4) until there is an excess of about 10 ml. Cool the contents of the separating funnel or of the extraction cylinder to about 25 °C and add 100 ml of the light petroleum (52). Insert the stopper and gently invert the separating funnel or the extraction cylinder, while maintaining a hold on the stopper. Open the stopcock of the separating funnel or the stopper of the extraction cylinder gradually to release any pressure, then close, gently shake and again release the pressure. Repeat the shaking until the water phase is clearly separated from the organic phase (if the two-phase layer is not obvious, the emulsification can be broken by adding ethanol that does not exceed the volume of the water phase), and then allow to stand. a) In the case of use of separating funnels Run off the aqueous layer into a second separating funnel (2) and extract with 50 ml of the light petroleum (52). Repeat the process, collect the aqueous layer in a conical flask and combine the three light petroleum extracts in the first separating funnel. b) In the case of use of an extraction cylinder Using a siphon. draw off the light petroleum layer completely as possible into a separating funnel (fz.2). Repeat the extraction twice with 50 ml of the light petroleum (52), combine the three light petroleum extracts in the separating funnel, transfer the aqueous layer as completely as possible to a conical flask and wash the extraction cylinder with small quantities of water, adding the washings to the conical flask. Wash the light petroleum extract by shaking with water (about 25 ml) until the washings are neutral to the methyl orange solution (51). Usually three washings are sufficient. Allow each wash to stand for at least...