JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
Detergent analysis. Abstract image of equipment used in the potentiometric titration of the bubble -forming (surfactant) chemicals in detergents. An electrode (at top centre) is emitting electric sparks down to bubbles in the lower frame. Many surfactants form water-soluble ions which have either a positive or negative charge. These ions will carry an electric current between two electrodes immersed in an aqueous solution of the detergent. If a known number of oppositely charged ions are added, the surfactant ions will combine with them and precipitate out of solution. The change in the current between the electrodes indicates the original number of surfactant ions.
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